Re: staging: r8188eu: how to handle nested mutex under spinlock

[Michael Straube]

On 4/3/22 12:49, Fabio M. De Francesco wrote:
> On domenica 3 aprile 2022 12:43:04 CEST Fabio M. De Francesco wrote:
> > On sabato 2 aprile 2022 22:47:27 CEST Michael Straube wrote:
> > > Hi all,
> > >
> > > smatch reported a sleeping in atomic context.
> > >
> > > rtw_set_802_11_disassociate() <- disables preempt
> > > -> _rtw_pwr_wakeup()
> > >      -> ips_leave()
> > >
> > > rtw_set_802_11_disassociate() takes a spinlock and ips_leave() uses a
> > > mutex.
> > >
> > > I'm fairly new to the locking stuff, but as far as I know this is not a
> > > false positive since mutex can sleep, but that's not allowed under a
> > > spinlock.
> > >
> > > What is the best way to handle this?
> > > I'm not sure if converting the mutex to a spinlock (including all the
> > > other places where the mutex is used) is the right thing to do?
> > >
> > > thanks,
> > > Michael
> > Hi Michael,
> >
> > No, this is a false positive: ips_leave is never called under spinlocks.
> > Some time ago I blindly trusted Smatch and submitted a patch for what you
> > are reporting just now again. Soon after submission I realized it and
> > then I had to ask Greg to discard my patch.
> >
> > Please read the related thread:
> >
> > [PATCH] staging: r8188eu: Use kzalloc() with GFP_ATOMIC in atomic context
> > https://lore.kernel.org/lkml/20220206225943.7848-1-fmdefrancesco@xxxxxxxxx/
> >
> > Thanks,
> >
> > Fabio
>
> I'm sorry, the correct link is the following:
> [PATCH v2 2/2] staging: r8188eu: Use kzalloc() with GFP_ATOMIC in atomic context
> https://lore.kernel.org/lkml/20220208180426.27455-3-fmdefrancesco@xxxxxxxxx/
>
> Fabio

Hi Fabio,

Ah I see now, thanks. Well, I think the code is not very clear and easy 
to follow here. Perhaps we should refactor this area someday to avoid 
future confusions.

regards,
Michael