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

[Jens Axboe <axboe@kernel.dk>]

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?

-- 
Jens Axboe