Commit 7ef3ff2f authored by Ryusuke Konishi's avatar Ryusuke Konishi Committed by Linus Torvalds

nilfs2: fix deadlock of segment constructor over I_SYNC flag

Nilfs2 eventually hangs in a stress test with fsstress program.  This
issue was caused by the following deadlock over I_SYNC flag between
nilfs_segctor_thread() and writeback_sb_inodes():

  nilfs_segctor_thread()
    nilfs_segctor_thread_construct()
      nilfs_segctor_unlock()
        nilfs_dispose_list()
          iput()
            iput_final()
              evict()
                inode_wait_for_writeback()  * wait for I_SYNC flag

  writeback_sb_inodes()
     * set I_SYNC flag on inode->i_state
    __writeback_single_inode()
      do_writepages()
        nilfs_writepages()
          nilfs_construct_dsync_segment()
            nilfs_segctor_sync()
               * wait for completion of segment constructor
    inode_sync_complete()
       * clear I_SYNC flag after __writeback_single_inode() completed

writeback_sb_inodes() calls do_writepages() for dirty inodes after
setting I_SYNC flag on inode->i_state.  do_writepages() in turn calls
nilfs_writepages(), which can run segment constructor and wait for its
completion.  On the other hand, segment constructor calls iput(), which
can call evict() and wait for the I_SYNC flag on
inode_wait_for_writeback().

Since segment constructor doesn't know when I_SYNC will be set, it
cannot know whether iput() will block or not unless inode->i_nlink has a
non-zero count.  We can prevent evict() from being called in iput() by
implementing sop->drop_inode(), but it's not preferable to leave inodes
with i_nlink == 0 for long periods because it even defers file
truncation and inode deallocation.  So, this instead resolves the
deadlock by calling iput() asynchronously with a workqueue for inodes
with i_nlink == 0.
Signed-off-by: default avatarRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Tested-by: default avatarRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 81cca6fb
......@@ -141,7 +141,6 @@ enum {
* @ti_save: Backup of journal_info field of task_struct
* @ti_flags: Flags
* @ti_count: Nest level
* @ti_garbage: List of inode to be put when releasing semaphore
*/
struct nilfs_transaction_info {
u32 ti_magic;
......@@ -150,7 +149,6 @@ struct nilfs_transaction_info {
one of other filesystems has a bug. */
unsigned short ti_flags;
unsigned short ti_count;
struct list_head ti_garbage;
};
/* ti_magic */
......
......@@ -305,7 +305,6 @@ static void nilfs_transaction_lock(struct super_block *sb,
ti->ti_count = 0;
ti->ti_save = cur_ti;
ti->ti_magic = NILFS_TI_MAGIC;
INIT_LIST_HEAD(&ti->ti_garbage);
current->journal_info = ti;
for (;;) {
......@@ -332,8 +331,6 @@ static void nilfs_transaction_unlock(struct super_block *sb)
up_write(&nilfs->ns_segctor_sem);
current->journal_info = ti->ti_save;
if (!list_empty(&ti->ti_garbage))
nilfs_dispose_list(nilfs, &ti->ti_garbage, 0);
}
static void *nilfs_segctor_map_segsum_entry(struct nilfs_sc_info *sci,
......@@ -746,6 +743,15 @@ static void nilfs_dispose_list(struct the_nilfs *nilfs,
}
}
static void nilfs_iput_work_func(struct work_struct *work)
{
struct nilfs_sc_info *sci = container_of(work, struct nilfs_sc_info,
sc_iput_work);
struct the_nilfs *nilfs = sci->sc_super->s_fs_info;
nilfs_dispose_list(nilfs, &sci->sc_iput_queue, 0);
}
static int nilfs_test_metadata_dirty(struct the_nilfs *nilfs,
struct nilfs_root *root)
{
......@@ -1900,8 +1906,8 @@ static int nilfs_segctor_collect_dirty_files(struct nilfs_sc_info *sci,
static void nilfs_segctor_drop_written_files(struct nilfs_sc_info *sci,
struct the_nilfs *nilfs)
{
struct nilfs_transaction_info *ti = current->journal_info;
struct nilfs_inode_info *ii, *n;
int defer_iput = false;
spin_lock(&nilfs->ns_inode_lock);
list_for_each_entry_safe(ii, n, &sci->sc_dirty_files, i_dirty) {
......@@ -1912,9 +1918,24 @@ static void nilfs_segctor_drop_written_files(struct nilfs_sc_info *sci,
clear_bit(NILFS_I_BUSY, &ii->i_state);
brelse(ii->i_bh);
ii->i_bh = NULL;
list_move_tail(&ii->i_dirty, &ti->ti_garbage);
list_del_init(&ii->i_dirty);
if (!ii->vfs_inode.i_nlink) {
/*
* Defer calling iput() to avoid a deadlock
* over I_SYNC flag for inodes with i_nlink == 0
*/
list_add_tail(&ii->i_dirty, &sci->sc_iput_queue);
defer_iput = true;
} else {
spin_unlock(&nilfs->ns_inode_lock);
iput(&ii->vfs_inode);
spin_lock(&nilfs->ns_inode_lock);
}
}
spin_unlock(&nilfs->ns_inode_lock);
if (defer_iput)
schedule_work(&sci->sc_iput_work);
}
/*
......@@ -2583,6 +2604,8 @@ static struct nilfs_sc_info *nilfs_segctor_new(struct super_block *sb,
INIT_LIST_HEAD(&sci->sc_segbufs);
INIT_LIST_HEAD(&sci->sc_write_logs);
INIT_LIST_HEAD(&sci->sc_gc_inodes);
INIT_LIST_HEAD(&sci->sc_iput_queue);
INIT_WORK(&sci->sc_iput_work, nilfs_iput_work_func);
init_timer(&sci->sc_timer);
sci->sc_interval = HZ * NILFS_SC_DEFAULT_TIMEOUT;
......@@ -2609,6 +2632,8 @@ static void nilfs_segctor_write_out(struct nilfs_sc_info *sci)
ret = nilfs_segctor_construct(sci, SC_LSEG_SR);
nilfs_transaction_unlock(sci->sc_super);
flush_work(&sci->sc_iput_work);
} while (ret && retrycount-- > 0);
}
......@@ -2633,6 +2658,9 @@ static void nilfs_segctor_destroy(struct nilfs_sc_info *sci)
|| sci->sc_seq_request != sci->sc_seq_done);
spin_unlock(&sci->sc_state_lock);
if (flush_work(&sci->sc_iput_work))
flag = true;
if (flag || !nilfs_segctor_confirm(sci))
nilfs_segctor_write_out(sci);
......@@ -2642,6 +2670,12 @@ static void nilfs_segctor_destroy(struct nilfs_sc_info *sci)
nilfs_dispose_list(nilfs, &sci->sc_dirty_files, 1);
}
if (!list_empty(&sci->sc_iput_queue)) {
nilfs_warning(sci->sc_super, __func__,
"iput queue is not empty\n");
nilfs_dispose_list(nilfs, &sci->sc_iput_queue, 1);
}
WARN_ON(!list_empty(&sci->sc_segbufs));
WARN_ON(!list_empty(&sci->sc_write_logs));
......
......@@ -26,6 +26,7 @@
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/buffer_head.h>
#include <linux/workqueue.h>
#include <linux/nilfs2_fs.h>
#include "nilfs.h"
......@@ -92,6 +93,8 @@ struct nilfs_segsum_pointer {
* @sc_nblk_inc: Block count of current generation
* @sc_dirty_files: List of files to be written
* @sc_gc_inodes: List of GC inodes having blocks to be written
* @sc_iput_queue: list of inodes for which iput should be done
* @sc_iput_work: work struct to defer iput call
* @sc_freesegs: array of segment numbers to be freed
* @sc_nfreesegs: number of segments on @sc_freesegs
* @sc_dsync_inode: inode whose data pages are written for a sync operation
......@@ -135,6 +138,8 @@ struct nilfs_sc_info {
struct list_head sc_dirty_files;
struct list_head sc_gc_inodes;
struct list_head sc_iput_queue;
struct work_struct sc_iput_work;
__u64 *sc_freesegs;
size_t sc_nfreesegs;
......
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