On 5/2/18 5:11 PM, je...@suse.com wrote:
> From: Jeff Mahoney <je...@suse.com>
>
> Commit 8d9eddad194 (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.
>
> Since the BTRFS_QGROUP_STATUS_FLAG_RESCAN flag is overloaded to
> refer to both runtime behavior and on-disk state, we introduce a new
> fs_info->qgroup_rescan_ready to indicate that we're initialized and
> waiting to start.
>
> This patch introduces a new helper, queue_rescan_worker, that handles
> most of the initialization, the two flags, and queuing the worker,
> including races with unmount.
>
> 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: 8d9eddad194 (Btrfs: fix qgroup rescan worker initialization)
> Signed-off-by: Jeff Mahoney <je...@suse.com>
> ---
> fs/btrfs/ctree.h | 2 ++
> fs/btrfs/qgroup.c | 94
> +++++++++++++++++++++++++++++++++----------------------
> 2 files changed, 58 insertions(+), 38 deletions(-)
>
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index da308774b8a4..4003498bb714 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -1045,6 +1045,8 @@ 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_ready;
> 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..466744741873 100644
> --- a/fs/btrfs/qgroup.c
> +++ b/fs/btrfs/qgroup.c
> @@ -101,6 +101,7 @@ static int
> qgroup_rescan_init(struct btrfs_fs_info *fs_info, u64 progress_objectid,
> int init_flags);
> static void qgroup_rescan_zero_tracking(struct btrfs_fs_info *fs_info);
> +static void btrfs_qgroup_rescan_worker(struct btrfs_work *work);
>
> /* must be called with qgroup_ioctl_lock held */
> static struct btrfs_qgroup *find_qgroup_rb(struct btrfs_fs_info *fs_info,
> @@ -2072,6 +2073,46 @@ 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_ready)) {
> + btrfs_warn(fs_info, "rescan worker not ready");
> + mutex_unlock(&fs_info->qgroup_rescan_lock);
> + return;
> + }
> + fs_info->qgroup_rescan_ready = false;
> +
> + 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;
> + init_completion(&fs_info->qgroup_rescan_completion);
> + mutex_unlock(&fs_info->qgroup_rescan_lock);
> +
> + memset(&fs_info->qgroup_rescan_work, 0,
> + sizeof(fs_info->qgroup_rescan_work));
> +
> + btrfs_init_work(&fs_info->qgroup_rescan_work,
> + btrfs_qgroup_rescan_helper,
> + btrfs_qgroup_rescan_worker, NULL, NULL);
> +
> + 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 +2164,7 @@ 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;
> }
> @@ -2607,6 +2647,10 @@ static void btrfs_qgroup_rescan_worker(struct
> btrfs_work *work)
> if (!path)
> goto out;
>
> + mutex_lock(&fs_info->qgroup_rescan_lock);
> + fs_info->qgroup_flags |= BTRFS_QGROUP_STATUS_FLAG_RESCAN;
> + mutex_unlock(&fs_info->qgroup_rescan_lock);
> +
> err = 0;
> while (!err && !btrfs_fs_closing(fs_info)) {
> trans = btrfs_start_transaction(fs_info->fs_root, 0);
> @@ -2685,47 +2729,27 @@ qgroup_rescan_init(struct btrfs_fs_info *fs_info, u64
> progress_objectid,
> {
> int ret = 0;
>
> - if (!init_flags &&
> - (!(fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_RESCAN) ||
> - !(fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_ON))) {
> + if (!test_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags)) {
> ret = -EINVAL;
> goto err;
> }
>
> mutex_lock(&fs_info->qgroup_rescan_lock);
> - spin_lock(&fs_info->qgroup_lock);
> -
> - if (init_flags) {
> - if (fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_RESCAN)
> - ret = -EINPROGRESS;
> - else if (!(fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_ON))
> - ret = -EINVAL;
> -
> - if (ret) {
> - spin_unlock(&fs_info->qgroup_lock);
> - mutex_unlock(&fs_info->qgroup_rescan_lock);
> - goto err;
> - }
> - fs_info->qgroup_flags |= BTRFS_QGROUP_STATUS_FLAG_RESCAN;
> + if (fs_info->qgroup_rescan_ready || fs_info->qgroup_rescan_running) {
> + mutex_unlock(&fs_info->qgroup_rescan_lock);
> + ret = -EINPROGRESS;
> + goto err;
> }
>
> memset(&fs_info->qgroup_rescan_progress, 0,
> 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;
> + fs_info->qgroup_rescan_ready = true;
>
> - spin_unlock(&fs_info->qgroup_lock);
> mutex_unlock(&fs_info->qgroup_rescan_lock);
>
> - memset(&fs_info->qgroup_rescan_work, 0,
> - sizeof(fs_info->qgroup_rescan_work));
> - btrfs_init_work(&fs_info->qgroup_rescan_work,
> - btrfs_qgroup_rescan_helper,
> - btrfs_qgroup_rescan_worker, NULL, NULL);
> -
> - if (ret) {
> err:
> + if (ret) {
> btrfs_info(fs_info, "qgroup_rescan_init failed with %d", ret);
> return ret;
> }
> @@ -2785,9 +2809,7 @@ 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 +2820,7 @@ 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 +2839,10 @@ 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)This check will never be true since the worker is now responsible for setting it. -Jeff > - btrfs_queue_work(fs_info->qgroup_rescan_workers, > - &fs_info->qgroup_rescan_work); > + queue_rescan_worker(fs_info); > } > > /* > -- Jeff Mahoney SUSE Labs
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