From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <52AA08EB.1080703@oracle.com> Date: Thu, 12 Dec 2013 14:05:15 -0500 From: Sasha Levin MIME-Version: 1.0 To: John Stultz , LKML CC: Thomas Gleixner , Prarit Bhargava , Richard Cochran , Ingo Molnar , stable Subject: Re: [RFC][PATCH 3/5] timekeeping: Avoid possible deadlock from clock_was_set_delayed References: <1386789098-17391-1-git-send-email-john.stultz@linaro.org> <1386789098-17391-4-git-send-email-john.stultz@linaro.org> <52A9E5B2.8040702@oracle.com> <52AA014B.6000301@oracle.com> <52AA0798.1050709@linaro.org> In-Reply-To: <52AA0798.1050709@linaro.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: On 12/12/2013 01:59 PM, John Stultz wrote: > On 12/12/2013 10:32 AM, Sasha Levin wrote: >> On 12/12/2013 11:34 AM, Sasha Levin wrote: >>> On 12/11/2013 02:11 PM, John Stultz wrote: >>>> As part of normal operaions, the hrtimer subsystem frequently calls >>>> into the timekeeping code, creating a locking order of >>>> hrtimer locks -> timekeeping locks >>>> >>>> clock_was_set_delayed() was suppoed to allow us to avoid deadlocks >>>> between the timekeeping the hrtimer subsystem, so that we could >>>> notify the hrtimer subsytem the time had changed while holding >>>> the timekeeping locks. This was done by scheduling delayed work >>>> that would run later once we were out of the timekeeing code. >>>> >>>> But unfortunately the lock chains are complex enoguh that in >>>> scheduling delayed work, we end up eventually trying to grab >>>> an hrtimer lock. >>>> >>>> Sasha Levin noticed this in testing when the new seqlock lockdep >>>> enablement triggered the following (somewhat abrieviated) message: >>> >>> [snip] >>> >>> This seems to work for me, I don't see the lockdep spew anymore. >>> >>> Tested-by: Sasha Levin >> >> I think I spoke too soon. >> >> It took way more time to reproduce than previously, but I got: >> >> >> -> #1 (&(&pool->lock)->rlock){-.-...}: >> [ 1195.578519] [] validate_chain+0x6c3/0x7b0 >> [ 1195.578519] [] __lock_acquire+0x4ad/0x580 >> [ 1195.578519] [] lock_acquire+0x182/0x1d0 >> [ 1195.578519] [] _raw_spin_lock+0x40/0x80 >> [ 1195.578519] [] __queue_work+0x14e/0x3f0 >> [ 1195.578519] [] queue_work_on+0x98/0x120 >> [ 1195.578519] [] >> clock_was_set_delayed+0x21/0x30 >> [ 1195.578519] [] do_adjtimex+0x111/0x160 >> [ 1195.578519] [] SYSC_adjtimex+0x43/0x80 >> [ 1195.578519] [] SyS_adjtimex+0xe/0x10 >> [ 1195.578519] [] tracesys+0xdd/0xe2 >> [ 1195.578519] > > Are you sure you have that patch applied? > > With it we shouldn't be calling clock_was_set_delayed() from do_adjtimex(). Hm, It seems that there's a conflict there that wasn't resolved properly. Does this patch depend on anything else that's not currently in -next? Thanks, Sasha