From: Marco Elver <elver@google.com>
To: "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
Cc: gregkh@linuxfoundation.org, jirislaby@kernel.org,
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com,
syzbot <syzbot+5f47a8cea6a12b77a876@syzkaller.appspotmail.com>
Subject: Re: [syzbot] BUG: sleeping function called from invalid context in __might_resched
Date: Fri, 12 Nov 2021 17:27:51 +0100 [thread overview]
Message-ID: <YY6WB9wMx/0VaqDx@elver.google.com> (raw)
In-Reply-To: <1805242.PYQNYDVmnG@localhost.localdomain>
On Fri, Nov 12, 2021 at 05:05PM +0100, Fabio M. De Francesco wrote:
> On Friday, November 12, 2021 2:58:14 PM CET Marco Elver wrote:
> > On Fri, 12 Nov 2021 at 13:22, Fabio M. De Francesco
> > <fmdefrancesco@gmail.com> wrote:
> > [...]
> > > I think that this "BUG" is a false positive.
> > >
> > > In do_con_write(), Just before the call of console_lock() there is an
> > > in_interrupt() check that, if it evaluates to true, makes this function to
> > > return "count" and prevents the SAC bug.
> >
> > It's not complaining about being in an interrupt, but rather
> > interrupts disabled, i.e. still an atomic context.
>
> Yes, still in an atomic context.
>
> Actually, I've never talked about being "in an interrupt", but I've just said
> that the in_interrupt() macro prevents to fall into the code that might
> sleep.
>
> Now I suppose that this is the place for in_atomic(). Isn't it?
in_atomic() probably won't do:
/*
* Are we running in atomic context? WARNING: this macro cannot
* always detect atomic context; in particular, it cannot know about
* held spinlocks in non-preemptible kernels. Thus it should not be
* used in the general case to determine whether sleeping is possible.
* Do not use in_atomic() in driver code.
*/
#define in_atomic() (preempt_count() != 0)
In particular, it doesn't detect if interrupts are disabled.
My guess is that in this case '!preemptible()' could work:
#define preemptible() (preempt_count() == 0 && !irqs_disabled())
But still am not entirely sure.
Thanks,
-- Marco
next prev parent reply other threads:[~2021-11-12 16:28 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-10 10:18 [syzbot] BUG: sleeping function called from invalid context in __might_resched syzbot
2021-11-12 12:22 ` Fabio M. De Francesco
2021-11-12 13:58 ` Marco Elver
2021-11-12 16:05 ` Fabio M. De Francesco
2021-11-12 16:27 ` Marco Elver [this message]
2021-11-12 17:15 ` Fabio M. De Francesco
2021-11-13 20:13 ` syzbot
2021-11-16 7:57 ` Fabio M. De Francesco
2021-11-16 8:09 ` syzbot
2021-11-16 8:53 ` Fabio M. De Francesco
2021-11-16 8:55 ` syzbot
2021-11-16 9:03 ` Fabio M. De Francesco
2021-11-16 9:03 ` syzbot
2021-11-16 9:20 ` syzbot
2021-11-16 9:13 ` Fabio M. De Francesco
2021-11-16 9:38 ` syzbot
2021-11-16 10:24 ` Marco Elver
2021-11-16 11:35 ` Fabio M. De Francesco
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