[PATCH 4.4 087/113] btrfs: properly track when rescan worker is running

Greg Kroah-Hartman
2016-09-05T16:55:26Z

From: Jeff Mahoney <jeffm@suse.com>

commit d2c609b834d62f1e91f1635a27dca29f7806d3d6 upstream.

The qgroup_flags field is overloaded such that it reflects the on-disk
status of qgroups and the runtime state. The BTRFS_QGROUP_STATUS_FLAG_RESCAN
flag is used to indicate that a rescan operation is in progress, but if
the file system is unmounted while a rescan is running, the rescan
operation is paused. If the file system is then mounted read-only,
the flag will still be present but the rescan operation will not have
been resumed. When we go to umount, btrfs_qgroup_wait_for_completion
will see the flag and interpret it to mean that the rescan worker is
still running and will wait for a completion that will never come.

This patch uses a separate flag to indicate when the worker is
running. The locking and state surrounding the qgroup rescan worker
needs a lot of attention beyond this patch but this is enough to
avoid a hung umount.

Signed-off-by; Jeff Mahoney <jeffm@suse.com>
Reviewed-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Signed-off-by: Chris Mason <clm@fb.com>

---
fs/btrfs/ctree.h | 1 +
fs/btrfs/disk-io.c | 1 +
fs/btrfs/qgroup.c | 9 ++++++++-
3 files changed, 10 insertions(+), 1 deletion(-)

--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1770,6 +1770,7 @@ struct btrfs_fs_info {
struct btrfs_workqueue *qgroup_rescan_workers;
struct completion qgroup_rescan_completion;
struct btrfs_work qgroup_rescan_work;
+ bool qgroup_rescan_running; /* protected by qgroup_rescan_lock */

/* filesystem state */
unsigned long fs_state;
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2276,6 +2276,7 @@ static void btrfs_init_qgroup(struct btr
fs_info->quota_enabled = 0;
fs_info->pending_quota_state = 0;
fs_info->qgroup_ulist = NULL;
+ fs_info->qgroup_rescan_running = false;
mutex_init(&fs_info->qgroup_rescan_lock);
}

--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -2283,6 +2283,10 @@ static void btrfs_qgroup_rescan_worker(s
int err = -ENOMEM;
int ret = 0;

+ mutex_lock(&fs_info->qgroup_rescan_lock);
+ fs_info->qgroup_rescan_running = true;
+ mutex_unlock(&fs_info->qgroup_rescan_lock);
+
path = btrfs_alloc_path();
if (!path)
goto out;
@@ -2349,6 +2353,9 @@ out:
}

done:
+ mutex_lock(&fs_info->qgroup_rescan_lock);
+ fs_info->qgroup_rescan_running = false;
+ mutex_unlock(&fs_info->qgroup_rescan_lock);
complete_all(&fs_info->qgroup_rescan_completion);
}

@@ -2475,7 +2482,7 @@ int btrfs_qgroup_wait_for_completion(str

mutex_lock(&fs_info->qgroup_rescan_lock);
spin_lock(&fs_info->qgroup_lock);
- running = fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_RESCAN;
+ running = fs_info->qgroup_rescan_running;
spin_unlock(&fs_info->qgroup_lock);
mutex_unlock(&fs_info->qgroup_rescan_lock);