Re: [PATCH 2/2] io_uring: don't hold uring_lock when calling io_run_task_work*

Hao Xu
2021-02-04T03:26:15Z

在 2021/2/4 上午12:45, Pavel Begunkov 写道:
> On 03/02/2021 16:35, Pavel Begunkov wrote:
>> On 03/02/2021 14:57, Hao Xu wrote:
>>> This is caused by calling io_run_task_work_sig() to do work under
>>> uring_lock while the caller io_sqe_files_unregister() already held
>>> uring_lock.
>>> we need to check if uring_lock is held by us when doing unlock around
>>> io_run_task_work_sig() since there are code paths down to that place
>>> without uring_lock held.
>>
>> 1. we don't want to allow parallel io_sqe_files_unregister()s
>> happening, it's synchronised by uring_lock atm. Otherwise it's
>> buggy.
Here "since there are code paths down to that place without uring_lock
held" I mean code path of io_ring_ctx_free().
>
> This one should be simple, alike to
>
> if (percpu_refs_is_dying())
> return error; // fail *files_unregister();
>
>>
>> 2. probably same with unregister and submit.
>>
>>>
>>> Reported-by: Abaci <abaci@linux.alibaba.com>
>>> Fixes: 1ffc54220c44 ("io_uring: fix io_sqe_files_unregister() hangs")
>>> Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
>>> ---
>>> fs/io_uring.c | 19 +++++++++++++------
>>> 1 file changed, 13 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>>> index efb6d02fea6f..b093977713ee 100644
>>> --- a/fs/io_uring.c
>>> +++ b/fs/io_uring.c
>>> @@ -7362,18 +7362,25 @@ static int io_sqe_files_unregister(struct io_ring_ctx *ctx, bool locked)
>>>
>>> /* wait for all refs nodes to complete */
>>> flush_delayed_work(&ctx->file_put_work);
>>> + if (locked)
>>> + mutex_unlock(&ctx->uring_lock);
>>> do {
>>> ret = wait_for_completion_interruptible(&data->done);
>>> if (!ret)
>>> break;
>>> ret = io_run_task_work_sig();
>>> - if (ret < 0) {
>>> - percpu_ref_resurrect(&data->refs);
>>> - reinit_completion(&data->done);
>>> - io_sqe_files_set_node(data, backup_node);
>>> - return ret;
>>> - }
>>> + if (ret < 0)
>>> + break;
>>> } while (1);
>>> + if (locked)
>>> + mutex_lock(&ctx->uring_lock);
>>> +
>>> + if (ret < 0) {
>>> + percpu_ref_resurrect(&data->refs);
>>> + reinit_completion(&data->done);
>>> + io_sqe_files_set_node(data, backup_node);
>>> + return ret;
>>> + }
>>>
>>> __io_sqe_files_unregister(ctx);
>>> nr_tables = DIV_ROUND_UP(ctx->nr_user_files, IORING_MAX_FILES_TABLE);
>>>
>>
>