From mboxrd@z Thu Jan 1 00:00:00 1970 From: k.kozlowski@samsung.com (Krzysztof Kozlowski) Date: Thu, 05 Feb 2015 08:46:06 +0100 Subject: [PATCH] ARM: Don't use complete() during __cpu_die In-Reply-To: <20150204175731.GH5370@linux.vnet.ibm.com> References: <1423068835-25470-1-git-send-email-k.kozlowski@samsung.com> <20150204175731.GH5370@linux.vnet.ibm.com> Message-ID: <1423122366.29408.9.camel@AMDC1943> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On ?ro, 2015-02-04 at 09:57 -0800, Paul E. McKenney wrote: > On Wed, Feb 04, 2015 at 05:53:55PM +0100, Krzysztof Kozlowski wrote: > > The complete() should not be used on offlined CPU. Rewrite the > > wait-complete mechanism with wait_on_bit_timeout(). > > > > The CPU triggering hot unplug (e.g. CPU0) will loop until some bit is > > cleared. In each iteration schedule_timeout() is used with initial sleep > > time of 1 ms. Later it is increased to 10 ms. > > > > The dying CPU will clear the bit which is safe in that context. > > > > This fixes following RCU warning on ARMv8 (Exynos 4412, Trats2) during > > suspend to RAM: > > > > [ 31.113925] =============================== > > [ 31.113928] [ INFO: suspicious RCU usage. ] > > [ 31.113935] 3.19.0-rc7-next-20150203 #1914 Not tainted > > [ 31.113938] ------------------------------- > > [ 31.113943] kernel/sched/fair.c:4740 suspicious rcu_dereference_check() usage! > > [ 31.113946] > > [ 31.113946] other info that might help us debug this: > > [ 31.113946] > > [ 31.113952] > > [ 31.113952] RCU used illegally from offline CPU! > > [ 31.113952] rcu_scheduler_active = 1, debug_locks = 0 > > [ 31.113957] 3 locks held by swapper/1/0: > > [ 31.113988] #0: ((cpu_died).wait.lock){......}, at: [] complete+0x14/0x44 > > [ 31.114012] #1: (&p->pi_lock){-.-.-.}, at: [] try_to_wake_up+0x28/0x300 > > [ 31.114035] #2: (rcu_read_lock){......}, at: [] select_task_rq_fair+0x5c/0xa04 > > [ 31.114038] > > [ 31.114038] stack backtrace: > > [ 31.114046] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 3.19.0-rc7-next-20150203 #1914 > > [ 31.114050] Hardware name: SAMSUNG EXYNOS (Flattened Device Tree) > > [ 31.114076] [] (unwind_backtrace) from [] (show_stack+0x10/0x14) > > [ 31.114091] [] (show_stack) from [] (dump_stack+0x70/0xbc) > > [ 31.114105] [] (dump_stack) from [] (select_task_rq_fair+0x6e0/0xa04) > > [ 31.114118] [] (select_task_rq_fair) from [] (try_to_wake_up+0xd4/0x300) > > [ 31.114129] [] (try_to_wake_up) from [] (__wake_up_common+0x4c/0x80) > > [ 31.114140] [] (__wake_up_common) from [] (__wake_up_locked+0x14/0x1c) > > [ 31.114150] [] (__wake_up_locked) from [] (complete+0x34/0x44) > > [ 31.114167] [] (complete) from [] (cpu_die+0x24/0x84) > > [ 31.114179] [] (cpu_die) from [] (cpu_startup_entry+0x328/0x358) > > [ 31.114189] [] (cpu_startup_entry) from [<40008784>] (0x40008784) > > [ 31.114226] CPU1: shutdown > > > > Signed-off-by: Krzysztof Kozlowski > > One suggestion below, but either way: > > Acked-by: Paul E. McKenney Thanks! > (If you would rather that I carried the patch, please let me know.) I'll send the patch through Russell's patch system. > > > --- > > arch/arm/kernel/smp.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++--- > > 1 file changed, 49 insertions(+), 3 deletions(-) > > > > diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c > > index 86ef244c5a24..bb8ff465975f 100644 > > --- a/arch/arm/kernel/smp.c > > +++ b/arch/arm/kernel/smp.c > > @@ -26,6 +26,7 @@ > > #include > > #include > > #include > > +#include > > > > #include > > #include > > @@ -76,6 +77,9 @@ enum ipi_msg_type { > > > > static DECLARE_COMPLETION(cpu_running); > > > > +#define CPU_DIE_WAIT_BIT 0 > > +static unsigned long wait_cpu_die; > > + > > static struct smp_operations smp_ops; > > > > void __init smp_set_ops(struct smp_operations *ops) > > @@ -133,6 +137,8 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle) > > pr_err("CPU%u: failed to boot: %d\n", cpu, ret); > > } > > > > + set_bit(CPU_DIE_WAIT_BIT, &wait_cpu_die); > > + smp_mb__after_atomic(); > > > > memset(&secondary_data, 0, sizeof(secondary_data)); > > return ret; > > @@ -213,7 +219,40 @@ int __cpu_disable(void) > > return 0; > > } > > > > -static DECLARE_COMPLETION(cpu_died); > > +/* > > + * Wait for 5000*1 ms for 'wait_cpu_die' bit to be cleared. > > + * Actually the real wait time will be longer because of schedule() > > + * called bit_wait_timeout. > > + * > > + * Returns 0 if bit was cleared (CPU died) or non-zero > > + * otherwise (1 or negative ERRNO). > > + */ > > +static int wait_for_cpu_die(void) > > +{ > > + int retries = 5000, sleep_ms = 1, ret = 0; > > + > > + might_sleep(); > > + > > + smp_mb__before_atomic(); > > + while (test_bit(CPU_DIE_WAIT_BIT, &wait_cpu_die)) { > > + ret = out_of_line_wait_on_bit_timeout(&wait_cpu_die, > > + CPU_DIE_WAIT_BIT, bit_wait_timeout, > > + TASK_UNINTERRUPTIBLE, > > + msecs_to_jiffies(sleep_ms)); > > + if (!ret || (--retries <= 0)) > > + break; > > + > > + if (retries < 4000) { > > + /* After ~1000 ms increase sleeping time to 10 ms */ > > + retries = 400; > > + sleep_ms = 10; > > + } > > Another approach that gets roughly the same response times with fewer > wakeups (and a bit less code) would be something like this: > > int ms_left = 5000, sleep_ms = 1, ret = 0; > > might_sleep(); > > smp_mb__before_atomic(); > while (test_bit(CPU_DIE_WAIT_BIT, &wait_cpu_die)) { > ret = out_of_line_wait_on_bit_timeout(&wait_cpu_die, > CPU_DIE_WAIT_BIT, bit_wait_timeout, > TASK_UNINTERRUPTIBLE, > msecs_to_jiffies(sleep_ms)); > ms_left -= sleep_ms; > if (!ret || (ms_left <= 0)) > break; > sleep_ms = DIV_ROUND_UP(sleep_ms * 11, 10); > > This would result in less than 50 wakeups compared to more than 4000, > with little added latency in the common case. > > But either way works for me. It looks better. I'll use it although Stephen Boyd had an other idea which could be smaller and more schedule-friendly. Thanks for review, Krzysztof > > > + > > + smp_mb__before_atomic(); /* For next test_bit() in loop */ > > + } > > + > > + return ret; > > +} > > > > /* > > * called on the thread which is asking for a CPU to be shutdown - > > @@ -221,7 +260,7 @@ static DECLARE_COMPLETION(cpu_died); > > */ > > void __cpu_die(unsigned int cpu) > > { > > - if (!wait_for_completion_timeout(&cpu_died, msecs_to_jiffies(5000))) { > > + if (wait_for_cpu_die()) { > > pr_err("CPU%u: cpu didn't die\n", cpu); > > return; > > } > > @@ -236,6 +275,10 @@ void __cpu_die(unsigned int cpu) > > */ > > if (!platform_cpu_kill(cpu)) > > pr_err("CPU%u: unable to kill\n", cpu); > > + > > + /* Prepare the bit for some next CPU die */ > > + set_bit(CPU_DIE_WAIT_BIT, &wait_cpu_die); > > + smp_mb__after_atomic(); > > } > > > > /* > > @@ -250,6 +293,8 @@ void __ref cpu_die(void) > > { > > unsigned int cpu = smp_processor_id(); > > > > + WARN_ON(!test_bit(CPU_DIE_WAIT_BIT, &wait_cpu_die)); > > + > > idle_task_exit(); > > > > local_irq_disable(); > > @@ -267,7 +312,8 @@ void __ref cpu_die(void) > > * this returns, power and/or clocks can be removed at any point > > * from this CPU and its cache by platform_cpu_kill(). > > */ > > - complete(&cpu_died); > > + clear_bit(CPU_DIE_WAIT_BIT, &wait_cpu_die); > > + smp_mb__after_atomic(); > > > > /* > > * Ensure that the cache lines associated with that completion are > > -- > > 1.9.1 > >