btrfs: qgroup: exit the rescan worker during umount (7343dd61) · Commits · 戴 / test

I was hitting a consistent NULL pointer dereference during shutdown that showed the trace running through end_workqueue_bio(). I traced it back to the endio_meta_workers workqueue being poked after it had already been destroyed. Eventually I found that the root cause was a qgroup rescan that was still in progress while we were stopping all the btrfs workers. Currently we explicitly pause balance and scrub operations in close_ctree(), but we do nothing to stop the qgroup rescan. We should probably be doing the same for qgroup rescan, but that's a much larger change. This small change is good enough to allow me to unmount without crashing. Signed-off-by:

Justin Maggard <jmaggard@netgear.com> Reviewed-by:

Filipe Manana <fdmanana@suse.com>

fs/btrfs/disk-io.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -3780,6 +3780,9 @@ void close_ctree(struct btrfs_root *root)
		fs_info->closing = 1;
		smp_mb();

		/* wait for the qgroup rescan worker to stop */
		btrfs_qgroup_wait_for_completion(fs_info);

		/* wait for the uuid_scan task to finish */
		down(&fs_info->uuid_tree_rescan_sem);
		/* avoid complains from lockdep et al., set sem back to initial state */

fs/btrfs/qgroup.c

+6 −3

Original line number	Diff line number	Diff line
		@@ -2286,7 +2286,7 @@ static void btrfs_qgroup_rescan_worker(struct btrfs_work *work)
		goto out;

		err = 0;
		while (!err) {
		while (!err && !btrfs_fs_closing(fs_info)) {
		trans = btrfs_start_transaction(fs_info->fs_root, 0);
		if (IS_ERR(trans)) {
		err = PTR_ERR(trans);
		@@ -2307,6 +2307,7 @@ out:
		btrfs_free_path(path);

		mutex_lock(&fs_info->qgroup_rescan_lock);
		if (!btrfs_fs_closing(fs_info))
		fs_info->qgroup_flags &= ~BTRFS_QGROUP_STATUS_FLAG_RESCAN;

		if (err > 0 &&
		@@ -2336,7 +2337,9 @@ out:
		}
		btrfs_end_transaction(trans, fs_info->quota_root);

		if (err >= 0) {
		if (btrfs_fs_closing(fs_info)) {
		btrfs_info(fs_info, "qgroup scan paused");
		} else if (err >= 0) {
		btrfs_info(fs_info, "qgroup scan completed%s",
		err > 0 ? " (inconsistency flag cleared)" : "");
		} else {

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