From: Filipe Manana Date: Thu, 8 Sep 2022 11:31:50 +0000 (+0100) Subject: btrfs: fix hang during unmount when stopping block group reclaim worker X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=8a1f1e3d1eecf9d2359a2709e276743a67e145db;p=people%2Fms%2Flinux.git btrfs: fix hang during unmount when stopping block group reclaim worker During early unmount, at close_ctree(), we try to stop the block group reclaim task with cancel_work_sync(), but that may hang if the block group reclaim task is currently at btrfs_relocate_block_group() waiting for the flag BTRFS_FS_UNFINISHED_DROPS to be cleared from fs_info->flags. During unmount we only clear that flag later, after trying to stop the block group reclaim task. Fix that by clearing BTRFS_FS_UNFINISHED_DROPS before trying to stop the block group reclaim task and after setting BTRFS_FS_CLOSING_START, so that if the reclaim task is waiting on that bit, it will stop immediately after being woken, because it sees the filesystem is closing (with a call to btrfs_fs_closing()), and then returns immediately with -EINTR. Fixes: 31e70e527806c5 ("btrfs: fix hang during unmount when block group reclaim task is running") CC: stable@vger.kernel.org # 5.15+ Reviewed-by: Josef Bacik Signed-off-by: Filipe Manana Signed-off-by: David Sterba --- diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c index 129711773ae5..9f844328b1e2 100644 --- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -4476,6 +4476,17 @@ void __cold close_ctree(struct btrfs_fs_info *fs_info) set_bit(BTRFS_FS_CLOSING_START, &fs_info->flags); + /* + * If we had UNFINISHED_DROPS we could still be processing them, so + * clear that bit and wake up relocation so it can stop. + * We must do this before stopping the block group reclaim task, because + * at btrfs_relocate_block_group() we wait for this bit, and after the + * wait we stop with -EINTR if btrfs_fs_closing() returns non-zero - we + * have just set BTRFS_FS_CLOSING_START, so btrfs_fs_closing() will + * return 1. + */ + btrfs_wake_unfinished_drop(fs_info); + /* * We may have the reclaim task running and relocating a data block group, * in which case it may create delayed iputs. So stop it before we park @@ -4494,12 +4505,6 @@ void __cold close_ctree(struct btrfs_fs_info *fs_info) */ kthread_park(fs_info->cleaner_kthread); - /* - * If we had UNFINISHED_DROPS we could still be processing them, so - * clear that bit and wake up relocation so it can stop. - */ - btrfs_wake_unfinished_drop(fs_info); - /* wait for the qgroup rescan worker to stop */ btrfs_qgroup_wait_for_completion(fs_info, false);