Re: [PATCH 2/2] io_uring: don't block level reissue off completion path

[Fabian Ebner <f.ebner@proxmox.com>]

Am 28.07.21 um 15:23 schrieb Jens Axboe:
> On 7/28/21 3:26 AM, Fabian Ebner wrote:
>> Am 27.07.21 um 18:58 schrieb Jens Axboe:
>>> Some setups, like SCSI, can throw spurious -EAGAIN off the softirq
>>> completion path. Normally we expect this to happen inline as part
>>> of submission, but apparently SCSI has a weird corner case where it
>>> can happen as part of normal completions.
>>>
>>> This should be solved by having the -EAGAIN bubble back up the stack
>>> as part of submission, but previous attempts at this failed and we're
>>> not just quite there yet. Instead we currently use REQ_F_REISSUE to
>>> handle this case.
>>>
>>> For now, catch it in io_rw_should_reissue() and prevent a reissue
>>> from a bogus path.
>>>
>>> Cc: stable@vger.kernel.org
>>> Reported-by: Fabian Ebner <f.ebner@proxmox.com>
>>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>>> ---
>>>    fs/io_uring.c | 6 ++++++
>>>    1 file changed, 6 insertions(+)
>>>
>>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>>> index 6ba101cd4661..83f67d33bf67 100644
>>> --- a/fs/io_uring.c
>>> +++ b/fs/io_uring.c
>>> @@ -2447,6 +2447,12 @@ static bool io_rw_should_reissue(struct io_kiocb *req)
>>>    	 */
>>>    	if (percpu_ref_is_dying(&ctx->refs))
>>>    		return false;
>>> +	/*
>>> +	 * Play it safe and assume not safe to re-import and reissue if we're
>>> +	 * not in the original thread group (or in task context).
>>> +	 */
>>> +	if (!same_thread_group(req->task, current) || !in_task())
>>> +		return false;
>>>    	return true;
>>>    }
>>>    #else
>>>
>>
>> Hi,
>>
>> thank you for the fix! This does indeed prevent the panic (with 5.11.22)
>> and hang (with 5.13.3) with my problematic workload.
> 
> Perfect, thanks for re-testing! Can I add your Tested-by to the patch?
> 

Sure, feel free to do so.

Best Regards,
Fabian