Re: [PATCH v3] PM-runtime: fix deadlock with ktime

From: Vincent Guittot
Date: Fri Feb 01 2019 - 10:48:34 EST

On Fri, 1 Feb 2019 at 16:44, Biju Das <biju.das@xxxxxxxxxxxxxx> wrote:
>
> Hi Vincent,
>
> Thanks for the feedback. Instead of reverting. I just modified the patch like this and it fixed the issue.
>
> diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
> index 4eaf166..145a182 100644
> --- a/drivers/base/power/runtime.c
> +++ b/drivers/base/power/runtime.c
> @@ -66,7 +66,7 @@ static int rpm_suspend(struct device *dev, int rpmflags);
> */
> void update_pm_runtime_accounting(struct device *dev)
> {
> - u64 now = ktime_to_ns(ktime_get());
> + u64 now = ktime_get_mono_fast_ns();
> u64 delta;

yes.
This probably also need to be changed in another place
(pm_runtime_enable) to be safe
Our email have crossed. I just sent something similar



>
> regards,
> Biju
>
> > -----Original Message-----
> > From: linux-renesas-soc-owner@xxxxxxxxxxxxxxx <linux-renesas-soc-
> > owner@xxxxxxxxxxxxxxx> On Behalf Of Vincent Guittot
> > Sent: 01 February 2019 15:29
> > To: Biju Das <biju.das@xxxxxxxxxxxxxx>
> > Cc: Rafael J. Wysocki <rafael@xxxxxxxxxx>; Linux PM <linux-
> > pm@xxxxxxxxxxxxxxx>; Linux Kernel Mailing List <linux-
> > kernel@xxxxxxxxxxxxxxx>; Linux ARM <linux-arm-
> > kernel@xxxxxxxxxxxxxxxxxxx>; Linux OMAP Mailing List <linux-
> > omap@xxxxxxxxxxxxxxx>; Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>; Ulf
> > Hansson <ulf.hansson@xxxxxxxxxx>; Geert Uytterhoeven <geert@linux-
> > m68k.org>; Linux-Renesas <linux-renesas-soc@xxxxxxxxxxxxxxx>
> > Subject: Re: [PATCH v3] PM-runtime: fix deadlock with ktime
> >
> > On Fri, 1 Feb 2019 at 16:02, Biju Das <biju.das@xxxxxxxxxxxxxx> 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@xxxxxxxxxx>
> > > > Sent: 30 January 2019 21:53
> > > > To: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
> > > > Cc: Linux PM <linux-pm@xxxxxxxxxxxxxxx>; Linux Kernel Mailing List
> > > > <linux- kernel@xxxxxxxxxxxxxxx>; Linux ARM <linux-arm-
> > > > kernel@xxxxxxxxxxxxxxxxxxx>; Linux OMAP Mailing List <linux-
> > > > omap@xxxxxxxxxxxxxxx>; Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>; Ulf
> > > > Hansson <ulf.hansson@xxxxxxxxxx>; Biju Das
> > > > <biju.das@xxxxxxxxxxxxxx>; Geert Uytterhoeven
> > > > <geert@xxxxxxxxxxxxxx>; Linux-Renesas <linux-
> > > > renesas-soc@xxxxxxxxxxxxxxx>
> > > > Subject: Re: [PATCH v3] PM-runtime: fix deadlock with ktime
> > > >
> > > > On Wed, Jan 30, 2019 at 6:26 PM Vincent Guittot
> > > > <vincent.guittot@xxxxxxxxxx> 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@xxxxxxxxxxxxxx>
> > > > > Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
> > > > > ---
> > > > >
> > > > > 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.
>
>
>
> Renesas Electronics Europe Ltd, Dukes Meadow, Millboard Road, Bourne End, Buckinghamshire, SL8 5FH, UK. Registered in England & Wales under Registered No. 04586709.