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Fri, 01 Feb 2019 07:45:44 -0800 (PST) Date: Fri, 1 Feb 2019 16:45:42 +0100 From: Vincent Guittot To: Biju Das Subject: Re: [PATCH v3] PM-runtime: fix deadlock with ktime Message-ID: <20190201154542.GA6174@linaro.org> References: <1548869162-6223-1-git-send-email-vincent.guittot@linaro.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190201_074547_680983_B22158D2 X-CRM114-Status: GOOD ( 35.86 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Ulf Hansson , Linux PM , "Rafael J. Wysocki" , "Rafael J. Wysocki" , Linux Kernel Mailing List , Linux-Renesas , Geert Uytterhoeven , Linux OMAP Mailing List , Linux ARM Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Le Friday 01 Feb 2019 =E0 16:28:54 (+0100), Vincent Guittot a =E9crit : > On Fri, 1 Feb 2019 at 16:02, Biju Das wrote: > > > > Hi Vincent, > > > > I have rebased my kernel to "next-20190201". Still I am seeing dead lo= ck. > > > > 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") ? Or instead you can apply : --- drivers/base/power/runtime.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c index 4eaf166..1c40e2a 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 =3D ktime_to_ns(ktime_get()); + u64 now =3D ktime_get_mono_fast_ns(); u64 delta; = delta =3D now - dev->power.accounting_timestamp; @@ -1315,7 +1315,7 @@ void pm_runtime_enable(struct device *dev) = /* About to enable runtime pm, set accounting_timestamp to now */ if (!dev->power.disable_depth) - dev->power.accounting_timestamp =3D ktime_to_ns(ktime_get()); + dev->power.accounting_timestamp =3D ktime_get_mono_fast_ns(); } else { dev_warn(dev, "Unbalanced %s!\n", __func__); } -- = 2.7.4 > > = > > > > root@ek874:/# echo e61e0000.timer > /sys/devices/system/clocksource/clo= cksource0/current_clocksource > > [ 193.869423] > > [ 193.870963] =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D > > [ 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_runt= ime_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: chang= e_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-n= ext-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 > > > Sent: 30 January 2019 21:53 > > > To: Vincent Guittot > > > Cc: Linux PM ; Linux Kernel Mailing List > > kernel@vger.kernel.org>; Linux ARM > > kernel@lists.infradead.org>; Linux OMAP Mailing List > > omap@vger.kernel.org>; Rafael J. Wysocki ; Ulf > > > Hansson ; Biju Das ; > > > Geert Uytterhoeven ; Linux-Renesas > > 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 > > > 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 ca= se > > > > > > > > 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 > > > > Signed-off-by: Vincent Guittot > > > > --- > > > > > > > > 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 En= d, Buckinghamshire, SL8 5FH, UK. Registered in England & Wales under Regist= ered No. 04586709. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel