From: Al Viro <viro@ZenIV.linux.org.uk>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>,
Sasha Levin <sasha.levin@oracle.com>,
akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
mingo@kernel.org
Subject: Re: [PATCH] signals: work around random wakeups in sigsuspend()
Date: Thu, 25 Feb 2016 17:34:23 +0000 [thread overview]
Message-ID: <20160225173423.GY17997@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20160225081144.GX6357@twins.programming.kicks-ass.net>
On Thu, Feb 25, 2016 at 09:11:44AM +0100, Peter Zijlstra wrote:
> > Out of curiousity - where did that stray wakeup come from? PTRACE_KILL
> > used to trigger those, but that got fixed. How does one trigger that
> > kind of bugs on the current kernels?
>
> Its a regular TASK_INTERRUPTIBLE sleep, for those spurious wakeups are
> not a bug, they're pretty fundamentally allowed.
They are, which makes any code that doesn't expect them in such situations
buggy.
> See: lkml.kernel.org/r/CA+55aFwHkOo+YGWKYROmce1-H_uG3KfEUmCkJUerTj=ojY2H6Q@mail.gmail.com
I know. The question is not whether the code must take them into account
(it must; it's a bug not to), it's what's a good way to trigger such bugs.
IOW, how to stress-test for such bugs?
PTRACE_KILL used to be a convenient way to arrange for a wakeup delivered
to victim engaged in something we want to stress; it doesn't do blind
wake_up_process() anymore, so that trick is gone. Is there anything
similar?
Suppose I have a dodgy waitqueue code (pardon the redundancy) in some
filesystem. I have some idea how to maneuver a process into such-and-such
part of that code; is there any convenient way to turn that into "... OK,
now let's add bombing it with stray wakeups"?
next prev parent reply other threads:[~2016-02-25 17:34 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-25 15:21 Sasha Levin
2016-01-25 19:09 ` Oleg Nesterov
2016-01-25 19:37 ` Peter Zijlstra
2016-02-25 3:18 ` Al Viro
2016-02-25 8:11 ` Peter Zijlstra
2016-02-25 17:34 ` Al Viro [this message]
2016-01-25 21:32 ` Andrew Morton
2016-01-26 21:10 ` Oleg Nesterov
2016-01-27 8:44 ` Peter Zijlstra
2016-01-27 16:41 ` Oleg Nesterov
2016-01-27 17:54 ` Peter Zijlstra
2016-01-27 18:39 ` Andrew Morton
2016-01-27 21:07 ` Oleg Nesterov
2016-01-27 17:24 ` Sasha Levin
2016-01-26 6:44 ` Ingo Molnar
2016-01-26 15:05 ` Oleg Nesterov
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