linux-kernel - Re: [PATCH 6.8 015/715] io_uring: remove unconditional looping in local task

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Date: Thu, 4 Apr 2024 09:06:56 +0200
From: Jiri Slaby <jirislaby@...nel.org>
To: Jens Axboe <axboe@...nel.dk>, Sasha Levin <sashal@...nel.org>,
 linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH 6.8 015/715] io_uring: remove unconditional looping in
 local task_work handling

On 02. 04. 24, 15:41, Jens Axboe wrote:
> On 4/2/24 2:12 AM, Jiri Slaby wrote:
>> On 24. 03. 24, 23:23, Sasha Levin wrote:
>>> From: Jens Axboe <axboe@...nel.dk>
>>>
>>> [ Upstream commit 9fe3eaea4a3530ca34a8d8ff00b1848c528789ca ]
>>>
>>> If we have a ton of notifications coming in, we can be looping in here
>>> for a long time. This can be problematic for various reasons, mostly
>>> because we can starve userspace. If the application is waiting on N
>>> events, then only re-run if we need more events.
>>
>> This commit breaks test/recv-multishot.c from liburing:
>> early error: res 4
>> test stream=1 wait_each=0 recvmsg=0 early_error=0  defer=1 failed
>>
>> The behaviour is the same in 6.9-rc2 (which contains the commit too).
>>
>> Reverting the commit on the top of 6.8.2 makes it pass again.
>>
>> Should the test be updated or is the commit wrong?
> 
> The commit is fine, it's the test that is buggy. Sometimes test cases
> make odd assumptions that are just wrong but happen to work, for some
> definition of work. Eg it would work fine on an idle system, but not
> necessarily if not. For this one, the fix is in liburing:
> 
> https://git.kernel.dk/cgit/liburing/commit/test/recv-multishot.c?id=a1d5e4b863a60af93d0cab9d4bbf578733337a90

Thanks, that worked.

Any plans to release 2.6 with the above?

Note that for 2.4->2.5 update I also needed to take 9dc95a03e4a76 from 
post-2.5.

thanks,
-- 
js
suse labs