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| author | Filipe Manana <fdmanana@suse.com> | 2015-11-05 10:06:23 +0000 |
|---|---|---|
| committer | Filipe Manana <fdmanana@suse.com> | 2015-11-05 10:32:21 +0000 |
| commit | 190631f1c8cb7e4d5c27ff87e22ed53817e78759 (patch) | |
| tree | a0b01561f6504793d66fe12351a784303fa2327d /fs | |
| parent | 7343dd61fd1b57c40cc06a5b5b5386df7f73c3ac (diff) | |
| download | linux-190631f1c8cb7e4d5c27ff87e22ed53817e78759.tar.gz linux-190631f1c8cb7e4d5c27ff87e22ed53817e78759.tar.bz2 linux-190631f1c8cb7e4d5c27ff87e22ed53817e78759.zip | |
Btrfs: fix race waiting for qgroup rescan worker
We were initializing the completion (fs_info->qgroup_rescan_completion)
object after releasing the qgroup rescan lock, which gives a small time
window for a rescan waiter to not actually wait for the rescan worker
to finish. Example:
CPU 1 CPU 2
fs_info->qgroup_rescan_completion->done is 0
btrfs_qgroup_rescan_worker()
complete_all(&fs_info->qgroup_rescan_completion)
sets fs_info->qgroup_rescan_completion->done
to UINT_MAX / 2
... do some other stuff ....
qgroup_rescan_init()
mutex_lock(&fs_info->qgroup_rescan_lock)
set flag BTRFS_QGROUP_STATUS_FLAG_RESCAN
in fs_info->qgroup_flags
mutex_unlock(&fs_info->qgroup_rescan_lock)
btrfs_qgroup_wait_for_completion()
mutex_lock(&fs_info->qgroup_rescan_lock)
sees flag BTRFS_QGROUP_STATUS_FLAG_RESCAN
in fs_info->qgroup_flags
mutex_unlock(&fs_info->qgroup_rescan_lock)
wait_for_completion_interruptible(
&fs_info->qgroup_rescan_completion)
fs_info->qgroup_rescan_completion->done
is > 0 so it returns immediately
init_completion(&fs_info->qgroup_rescan_completion)
sets fs_info->qgroup_rescan_completion->done to 0
So fix this by initializing the completion object while holding the mutex
fs_info->qgroup_rescan_lock.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/btrfs/qgroup.c | 3 |
1 files changed, 1 insertions, 2 deletions
diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c index 75c0249702df..75bb4af98a93 100644 --- a/fs/btrfs/qgroup.c +++ b/fs/btrfs/qgroup.c @@ -2387,12 +2387,11 @@ qgroup_rescan_init(struct btrfs_fs_info *fs_info, u64 progress_objectid, memset(&fs_info->qgroup_rescan_progress, 0, sizeof(fs_info->qgroup_rescan_progress)); fs_info->qgroup_rescan_progress.objectid = progress_objectid; + init_completion(&fs_info->qgroup_rescan_completion); spin_unlock(&fs_info->qgroup_lock); mutex_unlock(&fs_info->qgroup_rescan_lock); - init_completion(&fs_info->qgroup_rescan_completion); - memset(&fs_info->qgroup_rescan_work, 0, sizeof(fs_info->qgroup_rescan_work)); btrfs_init_work(&fs_info->qgroup_rescan_work, |