From 190631f1c8cb7e4d5c27ff87e22ed53817e78759 Mon Sep 17 00:00:00 2001 From: Filipe Manana Date: Thu, 5 Nov 2015 10:06:23 +0000 Subject: [PATCH] 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 --- fs/btrfs/qgroup.c | 3 +-- 1 file changed, 1 insertion(+), 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, -- GitLab