| Message ID | 1431467407-1223-8-git-send-email-paulmck@linux.vnet.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Paul, On Tue, May 12, 2015 at 11:50 PM, Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote: > From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> > > This commit removes the open-coded CPU-offline notification with new > common code. In particular, this change avoids calling scheduler code > using RCU from an offline CPU that RCU is ignoring. This is a minimal > change. A more intrusive change might invoke the cpu_check_up_prepare() > and cpu_set_state_online() functions at CPU-online time, which would > allow onlining throw an error if the CPU did not go offline properly. > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > Cc: linux-arm-kernel@lists.infradead.org > Cc: Russell King <linux@arm.linux.org.uk> Tested-by: Geert Uytterhoeven <geert+renesas@glider.be> Thanks, this seems to fix the intermittent "suspicious RCU usage" warnings I've been seeing during suspend to RAM on r8a7791/koelsch, which has a dual-core Cortex A15: Disabling non-boot CPUs ... =============================== [ INFO: suspicious RCU usage. ] 4.4.0-rc4-koelsch #2123 Tainted: G W ------------------------------- kernel/sched/fair.c:4938 suspicious rcu_dereference_check() usage! other info that might help us debug this: RCU used illegally from offline CPU! rcu_scheduler_active = 1, debug_locks = 0 3 locks held by swapper/1/0: #0: ((cpu_died).wait.lock){......}, at: [<c006077c>] complete+0x14/0x44 #1: (&p->pi_lock){-.-.-.}, at: [<c004b8a8>] try_to_wake_up+0x24/0x340 #2: (rcu_read_lock){......}, at: [<c0052740>] select_task_rq_fair+0xb4/0x820 stack backtrace: CPU: 1 PID: 0 Comm: swapper/1 Tainted: G W 4.4.0-rc4-koelsch #2123 Hardware name: Generic R8A7791 (Flattened Device Tree) [<c0017390>] (unwind_backtrace) from [<c0013094>] (show_stack+0x10/0x14) [<c0013094>] (show_stack) from [<c01ee718>] (dump_stack+0x70/0x8c) [<c01ee718>] (dump_stack) from [<c0052810>] (select_task_rq_fair+0x184/0x820) [<c0052810>] (select_task_rq_fair) from [<c004ba54>] (try_to_wake_up+0x1d0/0x340) [<c004ba54>] (try_to_wake_up) from [<c0060070>] (__wake_up_common+0x4c/0x78) [<c0060070>] (__wake_up_common) from [<c00600ac>] (__wake_up_locked+0x10/0x18) [<c00600ac>] (__wake_up_locked) from [<c006079c>] (complete+0x34/0x44) [<c006079c>] (complete) from [<c00159f8>] (arch_cpu_idle_dead+0x2c/0x8c) [<c00159f8>] (arch_cpu_idle_dead) from [<c0060a24>] (cpu_startup_entry+0x84/0x228) [<c0060a24>] (cpu_startup_entry) from [<4000a4ac>] (0x4000a4ac) CPU1: shutdown But I understand from the various other threads about this issue that this patch is not going upstream, as it papers over the real issue? Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c index cca5b8758185..8ef0ef0287ee 100644 --- a/arch/arm/kernel/smp.c +++ b/arch/arm/kernel/smp.c @@ -218,15 +218,13 @@ int __cpu_disable(void) return 0; } -static DECLARE_COMPLETION(cpu_died); - /* * called on the thread which is asking for a CPU to be shutdown - * waits until shutdown has completed, or it is timed out. */ void __cpu_die(unsigned int cpu) { - if (!wait_for_completion_timeout(&cpu_died, msecs_to_jiffies(5000))) { + if (!cpu_wait_death(cpu, 5)) { pr_err("CPU%u: cpu didn't die\n", cpu); return; } @@ -272,7 +270,7 @@ 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); + (void)cpu_report_death(); /* * Ensure that the cache lines associated with that completion are