btrfs: qgroup: exit the rescan worker during umount

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>

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 2d46675..1eb0839 100644 (file)
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -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 */

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 46476c2..75c0249 100644 (file)
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -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);
@@ -2307,7 +2307,8 @@ out:
        btrfs_free_path(path);
 
        mutex_lock(&fs_info->qgroup_rescan_lock);
-       fs_info->qgroup_flags &= ~BTRFS_QGROUP_STATUS_FLAG_RESCAN;
+       if (!btrfs_fs_closing(fs_info))
+               fs_info->qgroup_flags &= ~BTRFS_QGROUP_STATUS_FLAG_RESCAN;
 
        if (err > 0 &&
            fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_INCONSISTENT) {
@@ -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 {