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From: Thomas Gleixner <tglx@linutronix.de>
To: "Harris, Robert" <robert.harris@alertlogic.com>
Cc: Ingo Molnar <mingo@kernel.org>,
	"peterz@infradead.org" <peterz@infradead.org>,
	"dvhart@infradead.org" <dvhart@infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: Help requested: futex(..., FUTEX_WAIT_PRIVATE, ...) returns EPERM
Date: Wed, 13 Nov 2019 10:04:14 +0100 (CET)	[thread overview]
Message-ID: <alpine.DEB.2.21.1911130956150.1833@nanos.tec.linutronix.de> (raw)
In-Reply-To: <E0332978-739B-4546-9C3F-975216C349D2@alertlogic.com>

On Tue, 12 Nov 2019, Harris, Robert wrote:

> I am investigating an issue on 4.9.184 in which futex() returns EPERM
> intermittently for
> 
> futex(uaddr, FUTEX_WAIT_PRIVATE, val, &timeout, NULL, 0)
> 
> The failure affects an application in an AWS lambda;  traditional
> debugging approaches vary from difficult to impossible.  I cannot
> reproduce the problem at will, instrument the kernel, install a new
> kernel or get an application core dump.
> 
> Understanding the circumstances under which EPERM can be returned for
> FUTEX_WAIT_PRIVATE would be useful but it is not a documented failure
> mode.  I have spent some time looking through futex.c but have not
> found anything yet.  I would be grateful for a hint from someone more
> knowledgeable.

sys_futex(FUTEX_WAIT_PRIVATE) does not return -EPERM. Only the PI variants
do that.

Thanks,

	tglx

  parent reply	other threads:[~2019-11-13  9:04 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-12 17:40 Harris, Robert
2019-11-13  7:29 ` Harris, Robert
2019-11-13  9:04 ` Thomas Gleixner [this message]
2019-11-13 10:15   ` Harris, Robert
2019-11-13 21:34     ` Thomas Gleixner
2019-11-13 13:29 ` Mikael Pettersson
2019-11-13 17:03   ` Harris, Robert

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