From: Jeff Mahoney <jeffm@xxxxxxxx>
Commit d2c609b834d6 (Btrfs: fix qgroup rescan worker initialization)
fixed the issue with BTRFS_IOC_QUOTA_RESCAN_WAIT being racy, but
ended up reintroducing the hang-on-unmount bug that the commit it
intended to fix addressed.
The race this time is between qgroup_rescan_init setting
->qgroup_rescan_running = true and the worker starting. There are
many scenarios where we initialize the worker and never start it. The
completion btrfs_ioctl_quota_rescan_wait waits for will never come.
This can happen even without involving error handling, since mounting
the file system read-only returns between initializing the worker and
queueing it.
The right place to do it is when we're queuing the worker. The flag
really just means that btrfs_ioctl_quota_rescan_wait should wait for
a completion.
This patch introduces a new helper, queue_rescan_worker, that handles
the ->qgroup_rescan_running flag, including any races with umount.
While we're at it, ->qgroup_rescan_running is protected only by the
->qgroup_rescan_mutex. btrfs_ioctl_quota_rescan_wait doesn't need
to take the spinlock too.
Fixes: d2c609b834d6 (Btrfs: fix qgroup rescan worker initialization)
Signed-off-by: Jeff Mahoney <jeffm@xxxxxxxx>
---
fs/btrfs/ctree.h | 1 +
fs/btrfs/qgroup.c | 40 ++++++++++++++++++++++++++++------------
2 files changed, 29 insertions(+), 12 deletions(-)
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index da308774b8a4..dbba615f4d0f 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1045,6 +1045,7 @@ struct btrfs_fs_info {
struct btrfs_workqueue *qgroup_rescan_workers;
struct completion qgroup_rescan_completion;
struct btrfs_work qgroup_rescan_work;
+ /* qgroup rescan worker is running or queued to run */
bool qgroup_rescan_running; /* protected by qgroup_rescan_lock */
/* filesystem state */
diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index aa259d6986e1..be491b6c020a 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -2072,6 +2072,30 @@ int btrfs_qgroup_account_extents(struct btrfs_trans_handle *trans,
return ret;
}
+static void queue_rescan_worker(struct btrfs_fs_info *fs_info)
+{
+ mutex_lock(&fs_info->qgroup_rescan_lock);
+ if (btrfs_fs_closing(fs_info)) {
+ mutex_unlock(&fs_info->qgroup_rescan_lock);
+ return;
+ }
+ if (WARN_ON(fs_info->qgroup_rescan_running)) {
+ btrfs_warn(fs_info, "rescan worker already queued");
+ mutex_unlock(&fs_info->qgroup_rescan_lock);
+ return;
+ }
+
+ /*
+ * Being queued is enough for btrfs_qgroup_wait_for_completion
+ * to need to wait.
+ */
+ fs_info->qgroup_rescan_running = true;
+ mutex_unlock(&fs_info->qgroup_rescan_lock);
+
+ btrfs_queue_work(fs_info->qgroup_rescan_workers,
+ &fs_info->qgroup_rescan_work);
+}
+
/*
* called from commit_transaction. Writes all changed qgroups to disk.
*/
@@ -2123,8 +2147,7 @@ int btrfs_run_qgroups(struct btrfs_trans_handle *trans,
ret = qgroup_rescan_init(fs_info, 0, 1);
if (!ret) {
qgroup_rescan_zero_tracking(fs_info);
- btrfs_queue_work(fs_info->qgroup_rescan_workers,
- &fs_info->qgroup_rescan_work);
+ queue_rescan_worker(fs_info);
}
ret = 0;
}
@@ -2713,7 +2736,6 @@ qgroup_rescan_init(struct btrfs_fs_info *fs_info, u64 progress_objectid,
sizeof(fs_info->qgroup_rescan_progress));
fs_info->qgroup_rescan_progress.objectid = progress_objectid;
init_completion(&fs_info->qgroup_rescan_completion);
- fs_info->qgroup_rescan_running = true;
spin_unlock(&fs_info->qgroup_lock);
mutex_unlock(&fs_info->qgroup_rescan_lock);
@@ -2785,9 +2807,7 @@ btrfs_qgroup_rescan(struct btrfs_fs_info *fs_info)
qgroup_rescan_zero_tracking(fs_info);
- btrfs_queue_work(fs_info->qgroup_rescan_workers,
- &fs_info->qgroup_rescan_work);
-
+ queue_rescan_worker(fs_info);
return 0;
}
@@ -2798,9 +2818,7 @@ int btrfs_qgroup_wait_for_completion(struct btrfs_fs_info *fs_info,
int ret = 0;
mutex_lock(&fs_info->qgroup_rescan_lock);
- spin_lock(&fs_info->qgroup_lock);
running = fs_info->qgroup_rescan_running;
- spin_unlock(&fs_info->qgroup_lock);
mutex_unlock(&fs_info->qgroup_rescan_lock);
if (!running)
@@ -2819,12 +2837,10 @@ int btrfs_qgroup_wait_for_completion(struct btrfs_fs_info *fs_info,
* this is only called from open_ctree where we're still single threaded, thus
* locking is omitted here.
*/
-void
-btrfs_qgroup_rescan_resume(struct btrfs_fs_info *fs_info)
+void btrfs_qgroup_rescan_resume(struct btrfs_fs_info *fs_info)
{
if (fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_RESCAN)
- btrfs_queue_work(fs_info->qgroup_rescan_workers,
- &fs_info->qgroup_rescan_work);
+ queue_rescan_worker(fs_info);
}
/*
--
2.12.3
--
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