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SubjectRE: [PATCH v3] PM-runtime: fix deadlock with ktime
Date
Hi Vincent,

I have rebased my kernel to "next-20190201". Still I am seeing dead lock.

Am I missing any patch?

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!



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