On 4/30/18 2:20 AM, Qu Wenruo wrote:
>
>
> On 2018年04月27日 03:23, je...@suse.com wrote:
>> From: Jeff Mahoney <je...@suse.com>
>>
>> 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 <je...@suse.com>
>
> A little off-topic, (thanks Nikolay for reporting this) sometimes
> btrfs/017 could report qgroup corruption, and it turns out it's related
> to rescan racy, which double account existing tree blocks twice.
> (One by btrfs quota enable, another by btrfs quota rescan -w)
>
> Would this patch help in such case?
It shouldn't. This only fixes races between the rescan worker getting
initialized and running vs waiting for it to complete.
-Jeff
>> 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);
>> }
>>
>> /*
>>
>
--
Jeff Mahoney
SUSE Labs
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