Commit 027d6404 authored by Ryusuke Konishi's avatar Ryusuke Konishi
Browse files

nilfs2: use semaphore to protect pointer to a writable FS-instance

will get rid of nilfs_get_writer() and nilfs_put_writer() pair used to
retain a writable FS-instance for a period.

The pair functions were making up some kind of recursive lock with a
mutex, but they became overkill since the commit
201913ed

.  Furthermore, they caused
the following lockdep warning because the mutex can be released by a
task which didn't lock it:

 =====================================
 [ BUG: bad unlock balance detected! ]
 -------------------------------------
 kswapd0/422 is trying to release lock (&nilfs->ns_writer_mutex) at:
 [<c1359ff5>] mutex_unlock+0x8/0xa
 but there are no more locks to release!

 other info that might help us debug this:
 no locks held by kswapd0/422.

 stack backtrace:
 Pid: 422, comm: kswapd0 Not tainted 2.6.31-rc4-nilfs #51
 Call Trace:
  [<c1358f97>] ? printk+0xf/0x18
  [<c104fea7>] print_unlock_inbalance_bug+0xcc/0xd7
  [<c11578de>] ? prop_put_global+0x3/0x35
  [<c1050195>] lock_release+0xed/0x1dc
  [<c1359ff5>] ? mutex_unlock+0x8/0xa
  [<c1359f83>] __mutex_unlock_slowpath+0xaf/0x119
  [<c1359ff5>] mutex_unlock+0x8/0xa
  [<d1284add>] nilfs_mdt_write_page+0xd8/0xe1 [nilfs2]
  [<c1092653>] shrink_page_list+0x379/0x68d
  [<c109171b>] ? isolate_pages_global+0xb4/0x18c
  [<c1092bd2>] shrink_list+0x26b/0x54b
  [<c10930be>] shrink_zone+0x20c/0x2a2
  [<c10936b7>] kswapd+0x407/0x591
  [<c1091667>] ? isolate_pages_global+0x0/0x18c
  [<c1040603>] ? autoremove_wake_function+0x0/0x33
  [<c10932b0>] ? kswapd+0x0/0x591
  [<c104033b>] kthread+0x69/0x6e
  [<c10402d2>] ? kthread+0x0/0x6e
  [<c1003e33>] kernel_thread_helper+0x7/0x1a

This patch uses a reader/writer semaphore instead of the own lock and
kills this warning.
Signed-off-by: default avatarRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
parent b5696e5e
......@@ -402,6 +402,7 @@ nilfs_mdt_write_page(struct page *page, struct writeback_control *wbc)
struct inode *inode = container_of(page->mapping,
struct inode, i_data);
struct super_block *sb = inode->i_sb;
struct the_nilfs *nilfs = NILFS_MDT(inode)->mi_nilfs;
struct nilfs_sb_info *writer = NULL;
int err = 0;
......@@ -411,9 +412,10 @@ nilfs_mdt_write_page(struct page *page, struct writeback_control *wbc)
if (page->mapping->assoc_mapping)
return 0; /* Do not request flush for shadow page cache */
if (!sb) {
writer = nilfs_get_writer(NILFS_MDT(inode)->mi_nilfs);
down_read(&nilfs->ns_writer_sem);
writer = nilfs->ns_writer;
if (!writer) {
nilfs_put_writer(NILFS_MDT(inode)->mi_nilfs);
up_read(&nilfs->ns_writer_sem);
return -EROFS;
}
sb = writer->s_super;
......@@ -425,7 +427,7 @@ nilfs_mdt_write_page(struct page *page, struct writeback_control *wbc)
nilfs_flush_segment(sb, inode->i_ino);
if (writer)
nilfs_put_writer(NILFS_MDT(inode)->mi_nilfs);
up_read(&nilfs->ns_writer_sem);
return err;
}
......
......@@ -68,12 +68,11 @@ static struct the_nilfs *alloc_nilfs(struct block_device *bdev)
nilfs->ns_bdev = bdev;
atomic_set(&nilfs->ns_count, 1);
atomic_set(&nilfs->ns_writer_refcount, -1);
atomic_set(&nilfs->ns_ndirtyblks, 0);
init_rwsem(&nilfs->ns_sem);
init_rwsem(&nilfs->ns_super_sem);
mutex_init(&nilfs->ns_mount_mutex);
mutex_init(&nilfs->ns_writer_mutex);
init_rwsem(&nilfs->ns_writer_sem);
INIT_LIST_HEAD(&nilfs->ns_list);
INIT_LIST_HEAD(&nilfs->ns_supers);
spin_lock_init(&nilfs->ns_last_segment_lock);
......
......@@ -50,8 +50,7 @@ enum {
* @ns_sem: semaphore for shared states
* @ns_super_sem: semaphore for global operations across super block instances
* @ns_mount_mutex: mutex protecting mount process of nilfs
* @ns_writer_mutex: mutex protecting ns_writer attach/detach
* @ns_writer_refcount: number of referrers on ns_writer
* @ns_writer_sem: semaphore protecting ns_writer attach/detach
* @ns_current: back pointer to current mount
* @ns_sbh: buffer heads of on-disk super blocks
* @ns_sbp: pointers to super block data
......@@ -100,8 +99,7 @@ struct the_nilfs {
struct rw_semaphore ns_sem;
struct rw_semaphore ns_super_sem;
struct mutex ns_mount_mutex;
struct mutex ns_writer_mutex;
atomic_t ns_writer_refcount;
struct rw_semaphore ns_writer_sem;
/*
* components protected by ns_super_sem
......@@ -221,34 +219,21 @@ static inline void get_nilfs(struct the_nilfs *nilfs)
atomic_inc(&nilfs->ns_count);
}
static inline struct nilfs_sb_info *nilfs_get_writer(struct the_nilfs *nilfs)
{
if (atomic_inc_and_test(&nilfs->ns_writer_refcount))
mutex_lock(&nilfs->ns_writer_mutex);
return nilfs->ns_writer;
}
static inline void nilfs_put_writer(struct the_nilfs *nilfs)
{
if (atomic_add_negative(-1, &nilfs->ns_writer_refcount))
mutex_unlock(&nilfs->ns_writer_mutex);
}
static inline void
nilfs_attach_writer(struct the_nilfs *nilfs, struct nilfs_sb_info *sbi)
{
mutex_lock(&nilfs->ns_writer_mutex);
down_write(&nilfs->ns_writer_sem);
nilfs->ns_writer = sbi;
mutex_unlock(&nilfs->ns_writer_mutex);
up_write(&nilfs->ns_writer_sem);
}
static inline void
nilfs_detach_writer(struct the_nilfs *nilfs, struct nilfs_sb_info *sbi)
{
mutex_lock(&nilfs->ns_writer_mutex);
down_write(&nilfs->ns_writer_sem);
if (sbi == nilfs->ns_writer)
nilfs->ns_writer = NULL;
mutex_unlock(&nilfs->ns_writer_mutex);
up_write(&nilfs->ns_writer_sem);
}
static inline void nilfs_put_sbinfo(struct nilfs_sb_info *sbi)
......
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