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.
v3: avoid more races by calling btrfs_qgroup_wait_for_completion()
Signed-off-by: Justin Maggard <jmagg...@netgear.com>
---
fs/btrfs/disk-io.c | 3 +++
fs/btrfs/qgroup.c | 9 ++++++---
2 files changed, 9 insertions(+), 3 deletions(-)
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 2d46675..1eb0839 100644
--- 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
--- 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 {
--
2.6.2
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