glock.c 47 KB
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/*
 * Copyright (C) Sistina Software, Inc.  1997-2003 All rights reserved.
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 * Copyright (C) 2004-2006 Red Hat, Inc.  All rights reserved.
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 *
 * This copyrighted material is made available to anyone wishing to use,
 * modify, copy, or redistribute it subject to the terms and conditions
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 * of the GNU General Public License version 2.
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 */

#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/completion.h>
#include <linux/buffer_head.h>
#include <linux/delay.h>
#include <linux/sort.h>
#include <linux/jhash.h>
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#include <linux/kallsyms.h>
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#include <linux/gfs2_ondisk.h>
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#include <linux/list.h>
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#include <linux/lm_interface.h>
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#include <linux/wait.h>
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#include <linux/module.h>
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#include <linux/rwsem.h>
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#include <asm/uaccess.h>
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#include <linux/seq_file.h>
#include <linux/debugfs.h>
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#include "gfs2.h"
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#include "incore.h"
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#include "glock.h"
#include "glops.h"
#include "inode.h"
#include "lm.h"
#include "lops.h"
#include "meta_io.h"
#include "quota.h"
#include "super.h"
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#include "util.h"
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struct gfs2_gl_hash_bucket {
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        struct hlist_head hb_list;
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};

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struct glock_iter {
	int hash;                     /* hash bucket index         */
	struct gfs2_sbd *sdp;         /* incore superblock         */
	struct gfs2_glock *gl;        /* current glock struct      */
	struct hlist_head *hb_list;   /* current hash bucket ptr   */
	struct seq_file *seq;         /* sequence file for debugfs */
	char string[512];             /* scratch space             */
};

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typedef void (*glock_examiner) (struct gfs2_glock * gl);

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static int gfs2_dump_lockstate(struct gfs2_sbd *sdp);
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static void gfs2_glock_xmote_th(struct gfs2_glock *gl, struct gfs2_holder *gh);
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static void gfs2_glock_drop_th(struct gfs2_glock *gl);
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static DECLARE_RWSEM(gfs2_umount_flush_sem);
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static struct dentry *gfs2_root;
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#define GFS2_GL_HASH_SHIFT      15
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#define GFS2_GL_HASH_SIZE       (1 << GFS2_GL_HASH_SHIFT)
#define GFS2_GL_HASH_MASK       (GFS2_GL_HASH_SIZE - 1)

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static struct gfs2_gl_hash_bucket gl_hash_table[GFS2_GL_HASH_SIZE];
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/*
 * Despite what you might think, the numbers below are not arbitrary :-)
 * They are taken from the ipv4 routing hash code, which is well tested
 * and thus should be nearly optimal. Later on we might tweek the numbers
 * but for now this should be fine.
 *
 * The reason for putting the locks in a separate array from the list heads
 * is that we can have fewer locks than list heads and save memory. We use
 * the same hash function for both, but with a different hash mask.
 */
#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK) || \
	defined(CONFIG_PROVE_LOCKING)

#ifdef CONFIG_LOCKDEP
# define GL_HASH_LOCK_SZ        256
#else
# if NR_CPUS >= 32
#  define GL_HASH_LOCK_SZ       4096
# elif NR_CPUS >= 16
#  define GL_HASH_LOCK_SZ       2048
# elif NR_CPUS >= 8
#  define GL_HASH_LOCK_SZ       1024
# elif NR_CPUS >= 4
#  define GL_HASH_LOCK_SZ       512
# else
#  define GL_HASH_LOCK_SZ       256
# endif
#endif

/* We never want more locks than chains */
#if GFS2_GL_HASH_SIZE < GL_HASH_LOCK_SZ
# undef GL_HASH_LOCK_SZ
# define GL_HASH_LOCK_SZ GFS2_GL_HASH_SIZE
#endif

static rwlock_t gl_hash_locks[GL_HASH_LOCK_SZ];

static inline rwlock_t *gl_lock_addr(unsigned int x)
{
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	return &gl_hash_locks[x & (GL_HASH_LOCK_SZ-1)];
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}
#else /* not SMP, so no spinlocks required */
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static inline rwlock_t *gl_lock_addr(unsigned int x)
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{
	return NULL;
}
#endif
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/**
 * relaxed_state_ok - is a requested lock compatible with the current lock mode?
 * @actual: the current state of the lock
 * @requested: the lock state that was requested by the caller
 * @flags: the modifier flags passed in by the caller
 *
 * Returns: 1 if the locks are compatible, 0 otherwise
 */

static inline int relaxed_state_ok(unsigned int actual, unsigned requested,
				   int flags)
{
	if (actual == requested)
		return 1;

	if (flags & GL_EXACT)
		return 0;

	if (actual == LM_ST_EXCLUSIVE && requested == LM_ST_SHARED)
		return 1;

	if (actual != LM_ST_UNLOCKED && (flags & LM_FLAG_ANY))
		return 1;

	return 0;
}

/**
 * gl_hash() - Turn glock number into hash bucket number
 * @lock: The glock number
 *
 * Returns: The number of the corresponding hash bucket
 */

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static unsigned int gl_hash(const struct gfs2_sbd *sdp,
			    const struct lm_lockname *name)
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{
	unsigned int h;

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	h = jhash(&name->ln_number, sizeof(u64), 0);
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	h = jhash(&name->ln_type, sizeof(unsigned int), h);
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	h = jhash(&sdp, sizeof(struct gfs2_sbd *), h);
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	h &= GFS2_GL_HASH_MASK;

	return h;
}

/**
 * glock_free() - Perform a few checks and then release struct gfs2_glock
 * @gl: The glock to release
 *
 * Also calls lock module to release its internal structure for this glock.
 *
 */

static void glock_free(struct gfs2_glock *gl)
{
	struct gfs2_sbd *sdp = gl->gl_sbd;
	struct inode *aspace = gl->gl_aspace;

	gfs2_lm_put_lock(sdp, gl->gl_lock);

	if (aspace)
		gfs2_aspace_put(aspace);

	kmem_cache_free(gfs2_glock_cachep, gl);
}

/**
 * gfs2_glock_hold() - increment reference count on glock
 * @gl: The glock to hold
 *
 */

void gfs2_glock_hold(struct gfs2_glock *gl)
{
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	atomic_inc(&gl->gl_ref);
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}

/**
 * gfs2_glock_put() - Decrement reference count on glock
 * @gl: The glock to put
 *
 */

int gfs2_glock_put(struct gfs2_glock *gl)
{
	int rv = 0;
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	struct gfs2_sbd *sdp = gl->gl_sbd;
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	write_lock(gl_lock_addr(gl->gl_hash));
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	if (atomic_dec_and_test(&gl->gl_ref)) {
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		hlist_del(&gl->gl_list);
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		write_unlock(gl_lock_addr(gl->gl_hash));
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		BUG_ON(spin_is_locked(&gl->gl_spin));
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		gfs2_assert(sdp, gl->gl_state == LM_ST_UNLOCKED);
		gfs2_assert(sdp, list_empty(&gl->gl_reclaim));
		gfs2_assert(sdp, list_empty(&gl->gl_holders));
		gfs2_assert(sdp, list_empty(&gl->gl_waiters1));
		gfs2_assert(sdp, list_empty(&gl->gl_waiters3));
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		glock_free(gl);
		rv = 1;
		goto out;
	}
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	write_unlock(gl_lock_addr(gl->gl_hash));
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out:
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	return rv;
}

/**
 * search_bucket() - Find struct gfs2_glock by lock number
 * @bucket: the bucket to search
 * @name: The lock name
 *
 * Returns: NULL, or the struct gfs2_glock with the requested number
 */

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static struct gfs2_glock *search_bucket(unsigned int hash,
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					const struct gfs2_sbd *sdp,
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					const struct lm_lockname *name)
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{
	struct gfs2_glock *gl;
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	struct hlist_node *h;
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	hlist_for_each_entry(gl, h, &gl_hash_table[hash].hb_list, gl_list) {
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		if (!lm_name_equal(&gl->gl_name, name))
			continue;
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		if (gl->gl_sbd != sdp)
			continue;
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		atomic_inc(&gl->gl_ref);
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		return gl;
	}

	return NULL;
}

/**
 * gfs2_glock_find() - Find glock by lock number
 * @sdp: The GFS2 superblock
 * @name: The lock name
 *
 * Returns: NULL, or the struct gfs2_glock with the requested number
 */

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static struct gfs2_glock *gfs2_glock_find(const struct gfs2_sbd *sdp,
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					  const struct lm_lockname *name)
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{
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	unsigned int hash = gl_hash(sdp, name);
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	struct gfs2_glock *gl;

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	read_lock(gl_lock_addr(hash));
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	gl = search_bucket(hash, sdp, name);
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	read_unlock(gl_lock_addr(hash));
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	return gl;
}

/**
 * gfs2_glock_get() - Get a glock, or create one if one doesn't exist
 * @sdp: The GFS2 superblock
 * @number: the lock number
 * @glops: The glock_operations to use
 * @create: If 0, don't create the glock if it doesn't exist
 * @glp: the glock is returned here
 *
 * This does not lock a glock, just finds/creates structures for one.
 *
 * Returns: errno
 */

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int gfs2_glock_get(struct gfs2_sbd *sdp, u64 number,
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		   const struct gfs2_glock_operations *glops, int create,
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		   struct gfs2_glock **glp)
{
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	struct lm_lockname name = { .ln_number = number, .ln_type = glops->go_type };
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	struct gfs2_glock *gl, *tmp;
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	unsigned int hash = gl_hash(sdp, &name);
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	int error;

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	read_lock(gl_lock_addr(hash));
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	gl = search_bucket(hash, sdp, &name);
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	read_unlock(gl_lock_addr(hash));
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	if (gl || !create) {
		*glp = gl;
		return 0;
	}

	gl = kmem_cache_alloc(gfs2_glock_cachep, GFP_KERNEL);
	if (!gl)
		return -ENOMEM;

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	gl->gl_flags = 0;
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	gl->gl_name = name;
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	atomic_set(&gl->gl_ref, 1);
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	gl->gl_state = LM_ST_UNLOCKED;
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	gl->gl_hash = hash;
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	gl->gl_owner = NULL;
	gl->gl_ip = 0;
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	gl->gl_ops = glops;
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	gl->gl_req_gh = NULL;
	gl->gl_req_bh = NULL;
	gl->gl_vn = 0;
	gl->gl_stamp = jiffies;
	gl->gl_object = NULL;
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	gl->gl_sbd = sdp;
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	gl->gl_aspace = NULL;
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	lops_init_le(&gl->gl_le, &gfs2_glock_lops);

	/* If this glock protects actual on-disk data or metadata blocks,
	   create a VFS inode to manage the pages/buffers holding them. */
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	if (glops == &gfs2_inode_glops || glops == &gfs2_rgrp_glops) {
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		gl->gl_aspace = gfs2_aspace_get(sdp);
		if (!gl->gl_aspace) {
			error = -ENOMEM;
			goto fail;
		}
	}

	error = gfs2_lm_get_lock(sdp, &name, &gl->gl_lock);
	if (error)
		goto fail_aspace;

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	write_lock(gl_lock_addr(hash));
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	tmp = search_bucket(hash, sdp, &name);
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	if (tmp) {
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		write_unlock(gl_lock_addr(hash));
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		glock_free(gl);
		gl = tmp;
	} else {
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		hlist_add_head(&gl->gl_list, &gl_hash_table[hash].hb_list);
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		write_unlock(gl_lock_addr(hash));
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	}

	*glp = gl;

	return 0;

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fail_aspace:
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	if (gl->gl_aspace)
		gfs2_aspace_put(gl->gl_aspace);
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fail:
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	kmem_cache_free(gfs2_glock_cachep, gl);
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	return error;
}

/**
 * gfs2_holder_init - initialize a struct gfs2_holder in the default way
 * @gl: the glock
 * @state: the state we're requesting
 * @flags: the modifier flags
 * @gh: the holder structure
 *
 */

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void gfs2_holder_init(struct gfs2_glock *gl, unsigned int state, unsigned flags,
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		      struct gfs2_holder *gh)
{
	INIT_LIST_HEAD(&gh->gh_list);
	gh->gh_gl = gl;
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	gh->gh_ip = (unsigned long)__builtin_return_address(0);
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	gh->gh_owner = current;
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	gh->gh_state = state;
	gh->gh_flags = flags;
	gh->gh_error = 0;
	gh->gh_iflags = 0;
	gfs2_glock_hold(gl);
}

/**
 * gfs2_holder_reinit - reinitialize a struct gfs2_holder so we can requeue it
 * @state: the state we're requesting
 * @flags: the modifier flags
 * @gh: the holder structure
 *
 * Don't mess with the glock.
 *
 */

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void gfs2_holder_reinit(unsigned int state, unsigned flags, struct gfs2_holder *gh)
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{
	gh->gh_state = state;
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	gh->gh_flags = flags;
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	gh->gh_iflags = 0;
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	gh->gh_ip = (unsigned long)__builtin_return_address(0);
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}

/**
 * gfs2_holder_uninit - uninitialize a holder structure (drop glock reference)
 * @gh: the holder structure
 *
 */

void gfs2_holder_uninit(struct gfs2_holder *gh)
{
	gfs2_glock_put(gh->gh_gl);
	gh->gh_gl = NULL;
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	gh->gh_ip = 0;
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}

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static void gfs2_holder_wake(struct gfs2_holder *gh)
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{
	clear_bit(HIF_WAIT, &gh->gh_iflags);
	smp_mb();
	wake_up_bit(&gh->gh_iflags, HIF_WAIT);
}

static int holder_wait(void *word)
{
        schedule();
        return 0;
}

static void wait_on_holder(struct gfs2_holder *gh)
{
	might_sleep();
	wait_on_bit(&gh->gh_iflags, HIF_WAIT, holder_wait, TASK_UNINTERRUPTIBLE);
}

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/**
 * rq_mutex - process a mutex request in the queue
 * @gh: the glock holder
 *
 * Returns: 1 if the queue is blocked
 */

static int rq_mutex(struct gfs2_holder *gh)
{
	struct gfs2_glock *gl = gh->gh_gl;

	list_del_init(&gh->gh_list);
	/*  gh->gh_error never examined.  */
	set_bit(GLF_LOCK, &gl->gl_flags);
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	clear_bit(HIF_WAIT, &gh->gh_iflags);
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	smp_mb();
	wake_up_bit(&gh->gh_iflags, HIF_WAIT);
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	return 1;
}

/**
 * rq_promote - process a promote request in the queue
 * @gh: the glock holder
 *
 * Acquire a new inter-node lock, or change a lock state to more restrictive.
 *
 * Returns: 1 if the queue is blocked
 */

static int rq_promote(struct gfs2_holder *gh)
{
	struct gfs2_glock *gl = gh->gh_gl;
	struct gfs2_sbd *sdp = gl->gl_sbd;

	if (!relaxed_state_ok(gl->gl_state, gh->gh_state, gh->gh_flags)) {
		if (list_empty(&gl->gl_holders)) {
			gl->gl_req_gh = gh;
			set_bit(GLF_LOCK, &gl->gl_flags);
			spin_unlock(&gl->gl_spin);

			if (atomic_read(&sdp->sd_reclaim_count) >
			    gfs2_tune_get(sdp, gt_reclaim_limit) &&
			    !(gh->gh_flags & LM_FLAG_PRIORITY)) {
				gfs2_reclaim_glock(sdp);
				gfs2_reclaim_glock(sdp);
			}

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			gfs2_glock_xmote_th(gh->gh_gl, gh);
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			spin_lock(&gl->gl_spin);
		}
		return 1;
	}

	if (list_empty(&gl->gl_holders)) {
		set_bit(HIF_FIRST, &gh->gh_iflags);
		set_bit(GLF_LOCK, &gl->gl_flags);
	} else {
		struct gfs2_holder *next_gh;
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		if (gh->gh_state == LM_ST_EXCLUSIVE)
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			return 1;
		next_gh = list_entry(gl->gl_holders.next, struct gfs2_holder,
				     gh_list);
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		if (next_gh->gh_state == LM_ST_EXCLUSIVE)
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			 return 1;
	}

	list_move_tail(&gh->gh_list, &gl->gl_holders);
	gh->gh_error = 0;
	set_bit(HIF_HOLDER, &gh->gh_iflags);

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	gfs2_holder_wake(gh);
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	return 0;
}

/**
 * rq_demote - process a demote request in the queue
 * @gh: the glock holder
 *
 * Returns: 1 if the queue is blocked
 */

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static int rq_demote(struct gfs2_glock *gl)
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{
	if (!list_empty(&gl->gl_holders))
		return 1;

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	if (gl->gl_state == gl->gl_demote_state ||
	    gl->gl_state == LM_ST_UNLOCKED) {
		clear_bit(GLF_DEMOTE, &gl->gl_flags);
		return 0;
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	}
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	set_bit(GLF_LOCK, &gl->gl_flags);
	spin_unlock(&gl->gl_spin);
	if (gl->gl_demote_state == LM_ST_UNLOCKED ||
	    gl->gl_state != LM_ST_EXCLUSIVE)
		gfs2_glock_drop_th(gl);
	else
		gfs2_glock_xmote_th(gl, NULL);
	spin_lock(&gl->gl_spin);
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	return 0;
}

/**
 * run_queue - process holder structures on a glock
 * @gl: the glock
 *
 */
static void run_queue(struct gfs2_glock *gl)
{
	struct gfs2_holder *gh;
	int blocked = 1;

	for (;;) {
		if (test_bit(GLF_LOCK, &gl->gl_flags))
			break;

		if (!list_empty(&gl->gl_waiters1)) {
			gh = list_entry(gl->gl_waiters1.next,
					struct gfs2_holder, gh_list);

			if (test_bit(HIF_MUTEX, &gh->gh_iflags))
				blocked = rq_mutex(gh);
			else
				gfs2_assert_warn(gl->gl_sbd, 0);

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		} else if (test_bit(GLF_DEMOTE, &gl->gl_flags)) {
			blocked = rq_demote(gl);
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		} else if (!list_empty(&gl->gl_waiters3)) {
			gh = list_entry(gl->gl_waiters3.next,
					struct gfs2_holder, gh_list);

			if (test_bit(HIF_PROMOTE, &gh->gh_iflags))
				blocked = rq_promote(gh);
			else
				gfs2_assert_warn(gl->gl_sbd, 0);

		} else
			break;

		if (blocked)
			break;
	}
}

/**
 * gfs2_glmutex_lock - acquire a local lock on a glock
 * @gl: the glock
 *
 * Gives caller exclusive access to manipulate a glock structure.
 */

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static void gfs2_glmutex_lock(struct gfs2_glock *gl)
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{
	struct gfs2_holder gh;

	gfs2_holder_init(gl, 0, 0, &gh);
	set_bit(HIF_MUTEX, &gh.gh_iflags);
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	if (test_and_set_bit(HIF_WAIT, &gh.gh_iflags))
		BUG();
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	spin_lock(&gl->gl_spin);
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	if (test_and_set_bit(GLF_LOCK, &gl->gl_flags)) {
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		list_add_tail(&gh.gh_list, &gl->gl_waiters1);
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	} else {
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		gl->gl_owner = current;
		gl->gl_ip = (unsigned long)__builtin_return_address(0);
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		clear_bit(HIF_WAIT, &gh.gh_iflags);
		smp_mb();
		wake_up_bit(&gh.gh_iflags, HIF_WAIT);
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	}
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	spin_unlock(&gl->gl_spin);

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	wait_on_holder(&gh);
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	gfs2_holder_uninit(&gh);
}

/**
 * gfs2_glmutex_trylock - try to acquire a local lock on a glock
 * @gl: the glock
 *
 * Returns: 1 if the glock is acquired
 */

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static int gfs2_glmutex_trylock(struct gfs2_glock *gl)
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{
	int acquired = 1;

	spin_lock(&gl->gl_spin);
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	if (test_and_set_bit(GLF_LOCK, &gl->gl_flags)) {
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		acquired = 0;
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	} else {
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		gl->gl_owner = current;
		gl->gl_ip = (unsigned long)__builtin_return_address(0);
	}
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	spin_unlock(&gl->gl_spin);

	return acquired;
}

/**
 * gfs2_glmutex_unlock - release a local lock on a glock
 * @gl: the glock
 *
 */

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static void gfs2_glmutex_unlock(struct gfs2_glock *gl)
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{
	spin_lock(&gl->gl_spin);
	clear_bit(GLF_LOCK, &gl->gl_flags);
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	gl->gl_owner = NULL;
	gl->gl_ip = 0;
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	run_queue(gl);
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	BUG_ON(!spin_is_locked(&gl->gl_spin));
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	spin_unlock(&gl->gl_spin);
}

/**
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 * handle_callback - process a demote request
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 * @gl: the glock
 * @state: the state the caller wants us to change to
 *
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 * There are only two requests that we are going to see in actual
 * practise: LM_ST_SHARED and LM_ST_UNLOCKED
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 */

static void handle_callback(struct gfs2_glock *gl, unsigned int state)
{
	spin_lock(&gl->gl_spin);
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	if (test_and_set_bit(GLF_DEMOTE, &gl->gl_flags) == 0) {
		gl->gl_demote_state = state;
		gl->gl_demote_time = jiffies;
	} else if (gl->gl_demote_state != LM_ST_UNLOCKED) {
		gl->gl_demote_state = state;
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	}
	spin_unlock(&gl->gl_spin);
}

/**
 * state_change - record that the glock is now in a different state
 * @gl: the glock
 * @new_state the new state
 *
 */

static void state_change(struct gfs2_glock *gl, unsigned int new_state)
{
	int held1, held2;

	held1 = (gl->gl_state != LM_ST_UNLOCKED);
	held2 = (new_state != LM_ST_UNLOCKED);

	if (held1 != held2) {
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		if (held2)
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			gfs2_glock_hold(gl);
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		else
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			gfs2_glock_put(gl);
	}

	gl->gl_state = new_state;
}

/**
 * xmote_bh - Called after the lock module is done acquiring a lock
 * @gl: The glock in question
 * @ret: the int returned from the lock module
 *
 */

static void xmote_bh(struct gfs2_glock *gl, unsigned int ret)
{
	struct gfs2_sbd *sdp = gl->gl_sbd;
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	const struct gfs2_glock_operations *glops = gl->gl_ops;
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	struct gfs2_holder *gh = gl->gl_req_gh;
	int prev_state = gl->gl_state;
	int op_done = 1;

	gfs2_assert_warn(sdp, test_bit(GLF_LOCK, &gl->gl_flags));
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	gfs2_assert_warn(sdp, list_empty(&gl->gl_holders));
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	gfs2_assert_warn(sdp, !(ret & LM_OUT_ASYNC));

	state_change(gl, ret & LM_OUT_ST_MASK);

	if (prev_state != LM_ST_UNLOCKED && !(ret & LM_OUT_CACHEABLE)) {
		if (glops->go_inval)
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			glops->go_inval(gl, DIO_METADATA);
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	} else if (gl->gl_state == LM_ST_DEFERRED) {
		/* We might not want to do this here.
		   Look at moving to the inode glops. */
		if (glops->go_inval)
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			glops->go_inval(gl, 0);
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	}

	/*  Deal with each possible exit condition  */

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	if (!gh) {
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		gl->gl_stamp = jiffies;
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		if (ret & LM_OUT_CANCELED)
			op_done = 0;
		else
			clear_bit(GLF_DEMOTE, &gl->gl_flags);
	} else {
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		spin_lock(&gl->gl_spin);
		list_del_init(&gh->gh_list);
		gh->gh_error = -EIO;
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		if (unlikely(test_bit(SDF_SHUTDOWN, &sdp->sd_flags))) 
			goto out;
		gh->gh_error = GLR_CANCELED;
		if (ret & LM_OUT_CANCELED) 
			goto out;
		if (relaxed_state_ok(gl->gl_state, gh->gh_state, gh->gh_flags)) {
			list_add_tail(&gh->gh_list, &gl->gl_holders);
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			gh->gh_error = 0;
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			set_bit(HIF_HOLDER, &gh->gh_iflags);
			set_bit(HIF_FIRST, &gh->gh_iflags);
			op_done = 0;
			goto out;
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		}
		gh->gh_error = GLR_TRYFAILED;
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		if (gh->gh_flags & (LM_FLAG_TRY | LM_FLAG_TRY_1CB))
			goto out;
		gh->gh_error = -EINVAL;
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		if (gfs2_assert_withdraw(sdp, 0) == -1)
			fs_err(sdp, "ret = 0x%.8X\n", ret);
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out:
		spin_unlock(&gl->gl_spin);
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	}

	if (glops->go_xmote_bh)
		glops->go_xmote_bh(gl);

	if (op_done) {
		spin_lock(&gl->gl_spin);
		gl->gl_req_gh = NULL;
		gl->gl_req_bh = NULL;
		clear_bit(GLF_LOCK, &gl->gl_flags);
		run_queue(gl);
		spin_unlock(&gl->gl_spin);
	}

	gfs2_glock_put(gl);

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	if (gh)
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		gfs2_holder_wake(gh);
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}

/**
 * gfs2_glock_xmote_th - Call into the lock module to acquire or change a glock
 * @gl: The glock in question
 * @state: the requested state
 * @flags: modifier flags to the lock call
 *
 */

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void gfs2_glock_xmote_th(struct gfs2_glock *gl, struct gfs2_holder *gh)
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{
	struct gfs2_sbd *sdp = gl->gl_sbd;
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	int flags = gh ? gh->gh_flags : 0;
	unsigned state = gh ? gh->gh_state : gl->gl_demote_state;
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	const struct gfs2_glock_operations *glops = gl->gl_ops;
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	int lck_flags = flags & (LM_FLAG_TRY | LM_FLAG_TRY_1CB |
				 LM_FLAG_NOEXP | LM_FLAG_ANY |
				 LM_FLAG_PRIORITY);
	unsigned int lck_ret;

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	if (glops->go_xmote_th)
		glops->go_xmote_th(gl);

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	gfs2_assert_warn(sdp, test_bit(GLF_LOCK, &gl->gl_flags));
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	gfs2_assert_warn(sdp, list_empty(&gl->gl_holders));
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	gfs2_assert_warn(sdp, state != LM_ST_UNLOCKED);
	gfs2_assert_warn(sdp, state != gl->gl_state);

	gfs2_glock_hold(gl);
	gl->gl_req_bh = xmote_bh;

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	lck_ret = gfs2_lm_lock(sdp, gl->gl_lock, gl->gl_state, state, lck_flags);
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	if (gfs2_assert_withdraw(sdp, !(lck_ret & LM_OUT_ERROR)))
		return;

	if (lck_ret & LM_OUT_ASYNC)
		gfs2_assert_warn(sdp, lck_ret == LM_OUT_ASYNC);
	else
		xmote_bh(gl, lck_ret);
}

/**
 * drop_bh - Called after a lock module unlock completes
 * @gl: the glock
 * @ret: the return status
 *
 * Doesn't wake up the process waiting on the struct gfs2_holder (if any)
 * Doesn't drop the reference on the glock the top half took out
 *
 */

static void drop_bh(struct gfs2_glock *gl, unsigned int ret)
{
	struct gfs2_sbd *sdp = gl->gl_sbd;
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	const struct gfs2_glock_operations *glops = gl->gl_ops;
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	struct gfs2_holder *gh = gl->gl_req_gh;

	gfs2_assert_warn(sdp, test_bit(GLF_LOCK, &gl->gl_flags));
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	gfs2_assert_warn(sdp, list_empty(&gl->gl_holders));
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	gfs2_assert_warn(sdp, !ret);

	state_change(gl, LM_ST_UNLOCKED);
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	clear_bit(GLF_DEMOTE, &gl->gl_flags);
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	if (glops->go_inval)
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		glops->go_inval(gl, DIO_METADATA);
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	if (gh) {
		spin_lock(&gl->gl_spin);
		list_del_init(&gh->gh_list);
		gh->gh_error = 0;
		spin_unlock(&gl->gl_spin);
	}

	spin_lock(&gl->gl_spin);
	gl->gl_req_gh = NULL;
	gl->gl_req_bh = NULL;
	clear_bit(GLF_LOCK, &gl->gl_flags);
	run_queue(gl);
	spin_unlock(&gl->gl_spin);

	gfs2_glock_put(gl);

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	if (gh)
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		gfs2_holder_wake(gh);
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}

/**
 * gfs2_glock_drop_th - call into the lock module to unlock a lock
 * @gl: the glock
 *
 */

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static void gfs2_glock_drop_th(struct gfs2_glock *gl)
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{
	struct gfs2_sbd *sdp = gl->gl_sbd;
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	const struct gfs2_glock_operations *glops = gl->gl_ops;
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	unsigned int ret;

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	if (glops->go_drop_th)
		glops->go_drop_th(gl);

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	gfs2_assert_warn(sdp, test_bit(GLF_LOCK, &gl->gl_flags));
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	gfs2_assert_warn(sdp, list_empty(&gl->gl_holders));
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	gfs2_assert_warn(sdp, gl->gl_state != LM_ST_UNLOCKED);

	gfs2_glock_hold(gl);
	gl->gl_req_bh = drop_bh;

	ret = gfs2_lm_unlock(sdp, gl->gl_lock, gl->gl_state);

	if (gfs2_assert_withdraw(sdp, !(ret & LM_OUT_ERROR)))
		return;

	if (!ret)
		drop_bh(gl, ret);
	else
		gfs2_assert_warn(sdp, ret == LM_OUT_ASYNC);
}

/**
 * do_cancels - cancel requests for locks stuck waiting on an expire flag
 * @gh: the LM_FLAG_PRIORITY holder waiting to acquire the lock
 *
 * Don't cancel GL_NOCANCEL requests.
 */

static void do_cancels(struct gfs2_holder *gh)
{
	struct gfs2_glock *gl = gh->gh_gl;

	spin_lock(&gl->gl_spin);

	while (gl->gl_req_gh != gh &&
	       !test_bit(HIF_HOLDER, &gh->gh_iflags) &&
	       !list_empty(&gh->gh_list)) {
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		if (gl->gl_req_bh && !(gl->gl_req_gh &&
				     (gl->gl_req_gh->gh_flags & GL_NOCANCEL))) {
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			spin_unlock(&gl->gl_spin);
			gfs2_lm_cancel(gl->gl_sbd, gl->gl_lock);
			msleep(100);
			spin_lock(&gl->gl_spin);
		} else {
			spin_unlock(&gl->gl_spin);
			msleep(100);
			spin_lock(&gl->gl_spin);
		}
	}

	spin_unlock(&gl->gl_spin);
}

/**
 * glock_wait_internal - wait on a glock acquisition
 * @gh: the glock holder
 *
 * Returns: 0 on success
 */

static int glock_wait_internal(struct gfs2_holder *gh)
{
	struct gfs2_glock *gl = gh->gh_gl;
	struct gfs2_sbd *sdp = gl->gl_sbd;
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	const struct gfs2_glock_operations *glops = gl->gl_ops;
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	if (test_bit(HIF_ABORTED, &gh->gh_iflags))
		return -EIO;

	if (gh->gh_flags & (LM_FLAG_TRY | LM_FLAG_TRY_1CB)) {
		spin_lock(&gl->gl_spin);
		if (gl->gl_req_gh != gh &&
		    !test_bit(HIF_HOLDER, &gh->gh_iflags) &&
		    !list_empty(&gh->gh_list)) {
			list_del_init(&gh->gh_list);
			gh->gh_error = GLR_TRYFAILED;
			run_queue(gl);
			spin_unlock(&gl->gl_spin);
			return gh->gh_error;
		}
		spin_unlock(&gl->gl_spin);
	}

	if (gh->gh_flags & LM_FLAG_PRIORITY)
		do_cancels(gh);

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	wait_on_holder(gh);
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	if (gh->gh_error)
		return gh->gh_error;

	gfs2_assert_withdraw(sdp, test_bit(HIF_HOLDER, &gh->gh_iflags));
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	gfs2_assert_withdraw(sdp, relaxed_state_ok(gl->gl_state, gh->gh_state,
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						   gh->gh_flags));

	if (test_bit(HIF_FIRST, &gh->gh_iflags)) {
		gfs2_assert_warn(sdp, test_bit(GLF_LOCK, &gl->gl_flags));

		if (glops->go_lock) {
			gh->gh_error = glops->go_lock(gh);
			if (gh->gh_error) {
				spin_lock(&gl->gl_spin);
				list_del_init(&gh->gh_list);
				spin_unlock(&gl->gl_spin);
			}
		}

		spin_lock(&gl->gl_spin);
		gl->gl_req_gh = NULL;
		gl->gl_req_bh = NULL;
		clear_bit(GLF_LOCK, &gl->gl_flags);
		run_queue(gl);
		spin_unlock(&gl->gl_spin);
	}

	return gh->gh_error;
}

static inline struct gfs2_holder *
find_holder_by_owner(struct list_head *head, struct task_struct *owner)
{
	struct gfs2_holder *gh;

	list_for_each_entry(gh, head, gh_list) {
		if (gh->gh_owner == owner)
			return gh;
	}

	return NULL;
}

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static void print_dbg(struct glock_iter *gi, const char *fmt, ...)
{
	va_list args;

	va_start(args, fmt);
	if (gi) {
		vsprintf(gi->string, fmt, args);
		seq_printf(gi->seq, gi->string);
	}
	else
		vprintk(fmt, args);
	va_end(args);
}

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/**
 * add_to_queue - Add a holder to the wait queue (but look for recursion)
 * @gh: the holder structure to add
 *
 */

static void add_to_queue(struct gfs2_holder *gh)
{
	struct gfs2_glock *gl = gh->gh_gl;
	struct gfs2_holder *existing;

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	BUG_ON(!gh->gh_owner);
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	if (test_and_set_bit(HIF_WAIT, &gh->gh_iflags))
		BUG();
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	existing = find_holder_by_owner(&gl->gl_holders, gh->gh_owner);
	if (existing) {
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		print_symbol(KERN_WARNING "original: %s\n", existing->gh_ip);
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		printk(KERN_INFO "pid : %d\n", existing->gh_owner->pid);
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		printk(KERN_INFO "lock type : %d lock state : %d\n",
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				existing->gh_gl->gl_name.ln_type, existing->gh_gl->gl_state);
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		print_symbol(KERN_WARNING "new: %s\n", gh->gh_ip);
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		printk(KERN_INFO "pid : %d\n", gh->gh_owner->pid);
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		printk(KERN_INFO "lock type : %d lock state : %d\n",
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				gl->gl_name.ln_type, gl->gl_state);
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		BUG();
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	}

	existing = find_holder_by_owner(&gl->gl_waiters3, gh->gh_owner);
	if (existing) {
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		print_symbol(KERN_WARNING "original: %s\n", existing->gh_ip);
		print_symbol(KERN_WARNING "new: %s\n", gh->gh_ip);
		BUG();
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	}

	if (gh->gh_flags & LM_FLAG_PRIORITY)
		list_add(&gh->gh_list, &gl->gl_waiters3);
	else
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		list_add_tail(&gh->gh_list, &gl->gl_waiters3);
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}

/**
 * gfs2_glock_nq - enqueue a struct gfs2_holder onto a glock (acquire a glock)
 * @gh: the holder structure
 *
 * if (gh->gh_flags & GL_ASYNC), this never returns an error
 *
 * Returns: 0, GLR_TRYFAILED, or errno on failure
 */

int gfs2_glock_nq(struct gfs2_holder *gh)
{
	struct gfs2_glock *gl = gh->gh_gl;
	struct gfs2_sbd *sdp = gl->gl_sbd;
	int error = 0;

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restart:
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	if (unlikely(test_bit(SDF_SHUTDOWN, &sdp->sd_flags))) {
		set_bit(HIF_ABORTED, &gh->gh_iflags);
		return -EIO;
	}

	set_bit(HIF_PROMOTE, &gh->gh_iflags);

	spin_lock(&gl->gl_spin);
	add_to_queue(gh);
	run_queue(gl);
	spin_unlock(&gl->gl_spin);

	if (!(gh->gh_flags & GL_ASYNC)) {
		error = glock_wait_internal(gh);
		if (error == GLR_CANCELED) {
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			msleep(100);
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			goto restart;
		}
	}

	return error;
}

/**
 * gfs2_glock_poll - poll to see if an async request has been completed
 * @gh: the holder
 *
 * Returns: 1 if the request is ready to be gfs2_glock_wait()ed on
 */

int gfs2_glock_poll(struct gfs2_holder *gh)
{
	struct gfs2_glock *gl = gh->gh_gl;
	int ready = 0;

	spin_lock(&gl->gl_spin);

	if (test_bit(HIF_HOLDER, &gh->gh_iflags))
		ready = 1;
	else if (list_empty(&gh->gh_list)) {
		if (gh->gh_error == GLR_CANCELED) {
			spin_unlock(&gl->gl_spin);
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			msleep(100);
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			if (gfs2_glock_nq(gh))
				return 1;
			return 0;
		} else
			ready = 1;
	}

	spin_unlock(&gl->gl_spin);

	return ready;
}

/**
 * gfs2_glock_wait - wait for a lock acquisition that ended in a GLR_ASYNC
 * @gh: the holder structure
 *
 * Returns: 0, GLR_TRYFAILED, or errno on failure
 */

int gfs2_glock_wait(struct gfs2_holder *gh)
{
	int error;

	error = glock_wait_internal(gh);
	if (error == GLR_CANCELED) {
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		msleep(100);
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		gh->gh_flags &= ~GL_ASYNC;
		error = gfs2_glock_nq(gh);
	}

	return error;
}

/**
 * gfs2_glock_dq - dequeue a struct gfs2_holder from a glock (release a glock)
 * @gh: the glock holder
 *
 */

void gfs2_glock_dq(struct gfs2_holder *gh)
{
	struct gfs2_glock *gl = gh->gh_gl;
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	const struct gfs2_glock_operations *glops = gl->gl_ops;
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	if (gh->gh_flags & GL_NOCACHE)
		handle_callback(gl, LM_ST_UNLOCKED);

	gfs2_glmutex_lock(gl);

	spin_lock(&gl->gl_spin);
	list_del_init(&gh->gh_list);

	if (list_empty(&gl->gl_holders)) {
		spin_unlock(&gl->gl_spin);

		if (glops->go_unlock)
			glops->go_unlock(gh);

		spin_lock(&gl->gl_spin);
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		gl->gl_stamp = jiffies;
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	}

	clear_bit(GLF_LOCK, &gl->gl_flags);
	run_queue(gl);
	spin_unlock(&gl->gl_spin);
}

/**
 * gfs2_glock_dq_uninit - dequeue a holder from a glock and initialize it
 * @gh: the holder structure
 *
 */

void gfs2_glock_dq_uninit(struct gfs2_holder *gh)
{
	gfs2_glock_dq(gh);
	gfs2_holder_uninit(gh);
}

/**
 * gfs2_glock_nq_num - acquire a glock based on lock number
 * @sdp: the filesystem
 * @number: the lock number
 * @glops: the glock operations for the type of glock
 * @state: the state to acquire the glock in
 * @flags: modifier flags for the aquisition
 * @gh: the struct gfs2_holder
 *
 * Returns: errno
 */

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int gfs2_glock_nq_num(struct gfs2_sbd *sdp, u64 number,
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		      const struct gfs2_glock_operations *glops,
		      unsigned int state, int flags, struct gfs2_holder *gh)
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{
	struct gfs2_glock *gl;
	int error;

	error = gfs2_glock_get(sdp, number, glops, CREATE, &gl);
	if (!error) {
		error = gfs2_glock_nq_init(gl, state, flags, gh);
		gfs2_glock_put(gl);
	}

	return error;
}

/**
 * glock_compare - Compare two struct gfs2_glock structures for sorting
 * @arg_a: the first structure
 * @arg_b: the second structure
 *
 */

static int glock_compare(const void *arg_a, const void *arg_b)
{
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