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Btrfs: device_replace: fix deadlock for nocow case 

commit cb7ab02156 cause a following deadlock found by
xfstests,btrfs/011:

Thread1 is commiting transaction which is blocked at
btrfs_scrub_pause().

Thread2 is calling btrfs_file_aio_write() which has held
inode's @i_mutex and commit transaction(blocked because
Thread1 is committing transaction).

Thread3 is copy_nocow_page worker which will also try to
hold inode @i_mutex, so thread3 will wait Thread1 finished.

Thread4 is waiting pending workers finished which will wait
Thread3 finished. So the problem is like this:

Thread1--->Thread4--->Thread3--->Thread2---->Thread1

Deadlock happens! we fix it by letting Thread1 go firstly,
which means we won't block transaction commit while we are
waiting pending workers finished.

Reported-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
hifive-unleashed-5.1
Wang Shilong 2014-02-19 19:24:17 +08:00 committed by Josef Bacik
parent 6cf7f77e6b
commit 12cf93728d
1 changed files with 15 additions and 2 deletions
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17
fs/btrfs/scrub.c
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@ -2686,10 +2686,23 @@ int scrub_enumerate_chunks(struct scrub_ctx *sctx,
wait_event(sctx->list_wait,
atomic_read(&sctx->bios_in_flight) == 0);
atomic_set(&sctx->wr_ctx.flush_all_writes, 0);
atomic_inc(&fs_info->scrubs_paused);
wake_up(&fs_info->scrub_pause_wait);
/*
* must be called before we decrease @scrub_paused.
* make sure we don't block transaction commit while
* we are waiting pending workers finished.
*/
wait_event(sctx->list_wait,
atomic_read(&sctx->workers_pending) == 0);
scrub_blocked_if_needed(fs_info);
atomic_set(&sctx->wr_ctx.flush_all_writes, 0);
mutex_lock(&fs_info->scrub_lock);
__scrub_blocked_if_needed(fs_info);
atomic_dec(&fs_info->scrubs_paused);
mutex_unlock(&fs_info->scrub_lock);
wake_up(&fs_info->scrub_pause_wait);
btrfs_put_block_group(cache);
if (ret)