From: Stephen Boyd <sboyd@kernel.org>
To: Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
syzbot <syzbot+d6c75f383e01426a40b4@syzkaller.appspotmail.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
syzkaller-bugs@googlegroups.com, Waiman Long <llong@redhat.com>,
Paul E. McKenney <paulmck@kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>, Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [syzbot] WARNING in __init_work
Date: Tue, 21 Sep 2021 11:38:16 -0700 [thread overview]
Message-ID: <163224949689.3714697.17466968510780664239@swboyd.mtv.corp.google.com> (raw)
In-Reply-To: <87sfy07n69.ffs@tglx>
Quoting Thomas Gleixner (2021-09-19 05:41:18)
>
> Again, it cannot do that from a softirq because
> synchronize_rcu_expedited() might sleep.
>
> > Is it possible that object_is_on_stack() doesn't work in IRQ context?
> > I'm not really following along on x86 but I could see where
> > task_stack_page() gets the wrong "stack" pointer because the task has one
> > stack and the irq stack is some per-cpu dedicated allocation?
>
> Even if debug objects would support objects on irq stacks, the above is
> still bogus. But it does not and will not because the operations here
> have to be fully synchronous:
>
> init() -> queue() or arm() -> wait() -> destroy()
>
> because you obviously cannot queue work or arm a timer which are on stack
> and then leave the function without waiting for the operation to complete.
Is there some way to make it more obvious that initializing a timer or
work on the stack in an irq context is a NONO because we can't wait for
it? Maybe some sort of debugobjects call to might_sleep() when it's
being told the object is on the stack, or throwing a might_sleep() into
the initialization of any stack based timer or workqueue, or both?
>
> So these operations have to be synchronous which is a NONO when running
> in hard or soft interrupt context because waiting for the operation to
> complete is not possible there.
>
next prev parent reply other threads:[~2021-09-21 18:38 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-15 17:00 [syzbot] WARNING in __init_work syzbot
2021-09-15 23:14 ` Andrew Morton
2021-09-16 2:29 ` Stephen Boyd
2021-09-19 12:41 ` Thomas Gleixner
2021-09-20 4:03 ` Dave Chinner
2021-09-20 12:28 ` Christoph Hellwig
2021-09-20 12:38 ` Paul E. McKenney
2021-09-20 12:45 ` Christoph Hellwig
2021-09-20 12:54 ` Paul E. McKenney
2021-09-21 18:38 ` Stephen Boyd [this message]
2021-09-21 20:19 ` Thomas Gleixner
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