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SubjectRe: [PATCH v3] PM-runtime: fix deadlock with ktime
On Fri, 1 Feb 2019 at 16:02, Biju Das <biju.das@bp.renesas.com> wrote:
>
> Hi Vincent,
>
> I have rebased my kernel to "next-20190201". Still I am seeing dead lock.
>
> Am I missing any patch?

No you don't miss anything.
I think that it's the opposite.

Modification in time accounting in PM runtime has been queued but it
has not moved (yet) to ktime_get_mono_fast_ns()

Can you try to revert c669560be6c8 ("PM-runtime: Replace jiffies-based
accounting with ktime-based accounting") ?

>
> root@ek874:/# echo e61e0000.timer > /sys/devices/system/clocksource/clocksource0/current_clocksource
> [ 193.869423]
> [ 193.870963] ============================================
> [ 193.876292] WARNING: possible recursive locking detected
> [ 193.881625] 5.0.0-rc4-next-20190201-00007-g731346f #3 Not tainted
> [ 193.887737] --------------------------------------------
> [ 193.893066] migration/0/11 is trying to acquire lock:
> [ 193.898136] (____ptrval____) (tk_core.seq){----}, at: update_pm_runtime_accounting+0x14/0x68
> [ 193.906632]
> [ 193.906632] but task is already holding lock:
> [ 193.912483] (____ptrval____) (tk_core.seq){----}, at: multi_cpu_stop+0x8c/0x140
> [ 193.919828]
> [ 193.919828] other info that might help us debug this:
> [ 193.926377] Possible unsafe locking scenario:
> [ 193.926377]
> [ 193.932314] CPU0
> [ 193.934765] ----
> [ 193.937216] lock(tk_core.seq);
> [ 193.940453] lock(tk_core.seq);
> [ 193.943691]
> [ 193.943691] *** DEADLOCK ***
> [ 193.943691]
> [ 193.949634] May be due to missing lock nesting notation
> [ 193.949634]
> [ 193.956446] 3 locks held by migration/0/11:
> [ 193.960642] #0: (____ptrval____) (timekeeper_lock){-.-.}, at: change_clocksource+0x2c/0x118
> [ 193.969125] #1: (____ptrval____) (tk_core.seq){----}, at: multi_cpu_stop+0x8c/0x140
> [ 193.976903] #2: (____ptrval____) (&(&dev->power.lock)->rlock){....}, at: __pm_runtime_resume+0x40/0x98
> [ 193.986339]
> [ 193.986339] stack backtrace:
> [ 193.990715] CPU: 0 PID: 11 Comm: migration/0 Not tainted 5.0.0-rc4-next-20190201-00007-g731346f #3
> [ 193.999707] Hardware name: Silicon Linux RZ/G2E evaluation kit EK874 (CAT874 + CAT875) (DT)
> [ 194.008089] Call trace:
> [ 194.010553] dump_backtrace+0x0/0x178
> [ 194.014227] show_stack+0x14/0x20
> [ 194.017562] dump_stack+0xb0/0xec
> [ 194.020895] __lock_acquire+0xfb4/0x1c08
> [ 194.024832] lock_acquire+0xd0/0x268
> [ 194.028420] ktime_get+0x5c/0x108
> [ 194.031747] update_pm_runtime_accounting+0x14/0x68
> [ 194.036643] rpm_resume+0x4ec/0x698
> [ 194.040144] __pm_runtime_resume+0x50/0x98
> [ 194.044264] sh_tmu_enable.part.1+0x24/0x50
> [ 194.048462] sh_tmu_clocksource_enable+0x48/0x70
> [ 194.053097] change_clocksource+0x84/0x118
> [ 194.057208] multi_cpu_stop+0x8c/0x140
> [ 194.060970] cpu_stopper_thread+0xac/0x120
> [ 194.065087] smpboot_thread_fn+0x1ac/0x2c8
> [ 194.069198] kthread+0x128/0x130
> [ 194.072439] ret_from_fork+0x10/0x18
>
>
> Regards,
> Biju
>
> > -----Original Message-----
> > From: Rafael J. Wysocki <rafael@kernel.org>
> > Sent: 30 January 2019 21:53
> > To: Vincent Guittot <vincent.guittot@linaro.org>
> > Cc: Linux PM <linux-pm@vger.kernel.org>; Linux Kernel Mailing List <linux-
> > kernel@vger.kernel.org>; Linux ARM <linux-arm-
> > kernel@lists.infradead.org>; Linux OMAP Mailing List <linux-
> > omap@vger.kernel.org>; Rafael J. Wysocki <rjw@rjwysocki.net>; Ulf
> > Hansson <ulf.hansson@linaro.org>; Biju Das <biju.das@bp.renesas.com>;
> > Geert Uytterhoeven <geert@linux-m68k.org>; Linux-Renesas <linux-
> > renesas-soc@vger.kernel.org>
> > Subject: Re: [PATCH v3] PM-runtime: fix deadlock with ktime
> >
> > On Wed, Jan 30, 2019 at 6:26 PM Vincent Guittot
> > <vincent.guittot@linaro.org> wrote:
> > >
> > > A deadlock has been seen when swicthing clocksources which use PM
> > runtime.
> > > The call path is:
> > > change_clocksource
> > > ...
> > > write_seqcount_begin
> > > ...
> > > timekeeping_update
> > > ...
> > > sh_cmt_clocksource_enable
> > > ...
> > > rpm_resume
> > > pm_runtime_mark_last_busy
> > > ktime_get
> > > do
> > > read_seqcount_begin
> > > while read_seqcount_retry
> > > ....
> > > write_seqcount_end
> > >
> > > Although we should be safe because we haven't yet changed the
> > > clocksource at that time, we can't because of seqcount protection.
> > >
> > > Use ktime_get_mono_fast_ns() instead which is lock safe for such case
> > >
> > > With ktime_get_mono_fast_ns, the timestamp is not guaranteed to be
> > > monotonic across an update and as a result can goes backward.
> > > According to
> > > update_fast_timekeeper() description: "In the worst case, this can
> > > result is a slightly wrong timestamp (a few nanoseconds)". For PM
> > > runtime autosuspend, this means only that the suspend decision can be
> > > slightly sub optimal.
> > >
> > > Fixes: 8234f6734c5d ("PM-runtime: Switch autosuspend over to using
> > > hrtimers")
> > > Reported-by: Biju Das <biju.das@bp.renesas.com>
> > > Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
> > > ---
> > >
> > > Hi Rafael,
> > >
> > > Sorry, I sent the version with the typo mistake that generated the
> > > compilation error reported by kbuild-test-robot
> > >
> > > This version doesn't have the typo.
> >
> > OK, I've applied this one, thanks!
>
>
>
> Renesas Electronics Europe Ltd, Dukes Meadow, Millboard Road, Bourne End, Buckinghamshire, SL8 5FH, UK. Registered in England & Wales under Registered No. 04586709.

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