Re: [PATCH v4 0/2] workqueue: Add warnings and check WQ flags usage

[Tetsuo Handa]

On 2026/06/01 1:48, Tejun Heo wrote:
> Sorry for the slow reply - I'm off at the moment so my latency is high.
> 
>> syzbot is failing to test linux-next kernels due to commit 21c05ca88a54
>> ("workqueue: Add warnings and ensure one among WQ_PERCPU or WQ_UNBOUND is
>> present").
>> We can't tolerate linux-next being untested until all callers are fixed.
> 
> Which caller is breaking which tests?

It is https://syzkaller.appspot.com/bug?extid=d078cba4418e65f61984 .

Even 10 days of being unable to test linux-next tree
( https://lkml.kernel.org/r/1a9f53d4-6f48-4df8-a3d8-2b0e442a163a@xxxxxxxxxxxxxxxxxxx )
can cause difficulty of identifying a culprit.

> 
> Reverting 21c05ca88a54 is easy, but there's no clean point to do it: the
> warning is in the wq tree while the caller fixes are scattered across several
> subsystem trees, and there's no reasonable way to synchronize all of that
> outside mainline. If it's a specific caller breaking a test, fixing that one
> is the better path.
> 

I've spent more than one year for updating all in-tree users who are
flushing kernel global workqueues. Please see a message from Linus at
https://lkml.kernel.org/r/CAHk-=whWreGjEQ6yasspzBrNnS7EQiL+SknToWt=SzUh4XomyQ@xxxxxxxxxxxxxx .

Please never try to emit WARNING: or BUG: message just for letting developers
update their code. If you can't use panic() instead of WARN*() or BUG*(), you
should not use WARN*() or BUG*(). The patch author who changes the behavior of
in-tree code is responsible for updating all in-tree code.