From 5d2b86d90f7cc4a41316cef3d41560da6141f45c Mon Sep 17 00:00:00 2001 From: Don Zickus Date: Fri, 11 May 2012 14:41:13 -0400 Subject: Revert "x86, reboot: Use NMI instead of REBOOT_VECTOR to stop cpus" This reverts commit 3603a2512f9e69dc87914ba922eb4a0812b21cd6. Originally I wanted a better hammer to shutdown cpus during panic. However, this really steps on the toes of various spinlocks in the panic path. Sometimes it is easier to wait for the IRQ to become re-enabled to indictate the cpu left the critical region and then shutdown the cpu. The next patch moves the NMI addition after the IRQ part. To make it easier to see the logic of everything, revert this patch and apply the next simpler patch. Signed-off-by: Don Zickus Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/1336761675-24296-2-git-send-email-dzickus@redhat.com Signed-off-by: Ingo Molnar --- arch/x86/kernel/smp.c | 59 ++------------------------------------------------- 1 file changed, 2 insertions(+), 57 deletions(-) (limited to 'arch/x86/kernel/smp.c') diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c index 66c74f481cab..6d20f523bc4e 100644 --- a/arch/x86/kernel/smp.c +++ b/arch/x86/kernel/smp.c @@ -29,7 +29,6 @@ #include #include #include -#include /* * Some notes on x86 processor bugs affecting SMP operation: * @@ -149,60 +148,6 @@ void native_send_call_func_ipi(const struct cpumask *mask) free_cpumask_var(allbutself); } -static atomic_t stopping_cpu = ATOMIC_INIT(-1); - -static int smp_stop_nmi_callback(unsigned int val, struct pt_regs *regs) -{ - /* We are registered on stopping cpu too, avoid spurious NMI */ - if (raw_smp_processor_id() == atomic_read(&stopping_cpu)) - return NMI_HANDLED; - - stop_this_cpu(NULL); - - return NMI_HANDLED; -} - -static void native_nmi_stop_other_cpus(int wait) -{ - unsigned long flags; - unsigned long timeout; - - if (reboot_force) - return; - - /* - * Use an own vector here because smp_call_function - * does lots of things not suitable in a panic situation. - */ - if (num_online_cpus() > 1) { - /* did someone beat us here? */ - if (atomic_cmpxchg(&stopping_cpu, -1, safe_smp_processor_id()) != -1) - return; - - if (register_nmi_handler(NMI_LOCAL, smp_stop_nmi_callback, - NMI_FLAG_FIRST, "smp_stop")) - /* Note: we ignore failures here */ - return; - - /* sync above data before sending NMI */ - wmb(); - - apic->send_IPI_allbutself(NMI_VECTOR); - - /* - * Don't wait longer than a second if the caller - * didn't ask us to wait. - */ - timeout = USEC_PER_SEC; - while (num_online_cpus() > 1 && (wait || timeout--)) - udelay(1); - } - - local_irq_save(flags); - disable_local_APIC(); - local_irq_restore(flags); -} - /* * this function calls the 'stop' function on all other CPUs in the system. */ @@ -215,7 +160,7 @@ asmlinkage void smp_reboot_interrupt(void) irq_exit(); } -static void native_irq_stop_other_cpus(int wait) +static void native_stop_other_cpus(int wait) { unsigned long flags; unsigned long timeout; @@ -298,7 +243,7 @@ struct smp_ops smp_ops = { .smp_prepare_cpus = native_smp_prepare_cpus, .smp_cpus_done = native_smp_cpus_done, - .stop_other_cpus = native_nmi_stop_other_cpus, + .stop_other_cpus = native_stop_other_cpus, .smp_send_reschedule = native_smp_send_reschedule, .cpu_up = native_cpu_up, -- cgit v1.2.3 From 7d007d21e539dbecb6942c5734e6649f720982cf Mon Sep 17 00:00:00 2001 From: Don Zickus Date: Fri, 11 May 2012 14:41:14 -0400 Subject: x86/reboot: Use NMI to assist in shutting down if IRQ fails For v3.3, I added code to use the NMI to stop other cpus in the panic case. The idea was to make sure all cpus on the system were definitely halted to help serialize the panic path to execute the rest of the code on a single cpu. The main problem it was trying to solve was how to stop a cpu that was spinning with its irqs disabled. A IPI irq would be stuck and couldn't get in there, but an NMI could. Things were great until we had another conversation about some pstore changes. Because some of the backend pstore still uses spinlocks to protect the device access, things could get ugly if a panic happened and we were stuck spinning on a lock. Now with the NMI shutting down cpus, we could assume no other cpus were running and just bust the spin lock and proceed. The counter argument was, well if you do that the backend could be in a screwed up state and you might not be able to save anything as a result. If we could have just given the cpu a little more time to finish things, we could have grabbed the spin lock cleanly and everything would have been fine. Well, how do give a cpu a 'little more time' in the panic case? For the most part you can't without spinning on the lock and even in that case, how long do you spin for? So instead of making it ugly in the pstore code, just mimic the idea that stop_machine had, which is block on an IRQ IPI until the remote cpu has re-enabled interrupts and left the critical region. Which is what happens now using REBOOT_IRQ. Then leave the NMI case for those cpus that are truly stuck after a short time. This leaves the current behaviour alone and just handle a corner case. Most systems should never have to enter the NMI code and if they do, print out a message in case the NMI itself causes another issue. Signed-off-by: Don Zickus Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/1336761675-24296-3-git-send-email-dzickus@redhat.com Signed-off-by: Ingo Molnar --- arch/x86/kernel/smp.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 56 insertions(+), 5 deletions(-) (limited to 'arch/x86/kernel/smp.c') diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c index 6d20f523bc4e..228e7405511a 100644 --- a/arch/x86/kernel/smp.c +++ b/arch/x86/kernel/smp.c @@ -29,6 +29,7 @@ #include #include #include +#include /* * Some notes on x86 processor bugs affecting SMP operation: * @@ -108,6 +109,8 @@ * about nothing of note with C stepping upwards. */ +static atomic_t stopping_cpu = ATOMIC_INIT(-1); + /* * this function sends a 'reschedule' IPI to another CPU. * it goes straight through and wastes no time serializing @@ -148,6 +151,17 @@ void native_send_call_func_ipi(const struct cpumask *mask) free_cpumask_var(allbutself); } +static int smp_stop_nmi_callback(unsigned int val, struct pt_regs *regs) +{ + /* We are registered on stopping cpu too, avoid spurious NMI */ + if (raw_smp_processor_id() == atomic_read(&stopping_cpu)) + return NMI_HANDLED; + + stop_this_cpu(NULL); + + return NMI_HANDLED; +} + /* * this function calls the 'stop' function on all other CPUs in the system. */ @@ -171,13 +185,25 @@ static void native_stop_other_cpus(int wait) /* * Use an own vector here because smp_call_function * does lots of things not suitable in a panic situation. - * On most systems we could also use an NMI here, - * but there are a few systems around where NMI - * is problematic so stay with an non NMI for now - * (this implies we cannot stop CPUs spinning with irq off - * currently) + */ + + /* + * We start by using the REBOOT_VECTOR irq. + * The irq is treated as a sync point to allow critical + * regions of code on other cpus to release their spin locks + * and re-enable irqs. Jumping straight to an NMI might + * accidentally cause deadlocks with further shutdown/panic + * code. By syncing, we give the cpus up to one second to + * finish their work before we force them off with the NMI. */ if (num_online_cpus() > 1) { + /* did someone beat us here? */ + if (atomic_cmpxchg(&stopping_cpu, -1, safe_smp_processor_id()) != -1) + return; + + /* sync above data before sending IRQ */ + wmb(); + apic->send_IPI_allbutself(REBOOT_VECTOR); /* @@ -188,7 +214,32 @@ static void native_stop_other_cpus(int wait) while (num_online_cpus() > 1 && (wait || timeout--)) udelay(1); } + + /* if the REBOOT_VECTOR didn't work, try with the NMI */ + if ((num_online_cpus() > 1)) { + if (register_nmi_handler(NMI_LOCAL, smp_stop_nmi_callback, + NMI_FLAG_FIRST, "smp_stop")) + /* Note: we ignore failures here */ + /* Hope the REBOOT_IRQ is good enough */ + goto finish; + + /* sync above data before sending IRQ */ + wmb(); + + pr_emerg("Shutting down cpus with NMI\n"); + + apic->send_IPI_allbutself(NMI_VECTOR); + + /* + * Don't wait longer than a 10 ms if the caller + * didn't ask us to wait. + */ + timeout = USEC_PER_MSEC * 10; + while (num_online_cpus() > 1 && (wait || timeout--)) + udelay(1); + } +finish: local_irq_save(flags); disable_local_APIC(); local_irq_restore(flags); -- cgit v1.2.3 From 3aac27aba79b7c52e709ef6de0f7d8139caedc01 Mon Sep 17 00:00:00 2001 From: Don Zickus Date: Fri, 11 May 2012 14:41:15 -0400 Subject: x86/reboot: Update nonmi_ipi parameter Update the nonmi_ipi parameter to reflect the simple change instead of the previous complicated one. There should be less of a need to use it but there may still be corner cases on older hardware that stumble into NMI issues. Signed-off-by: Don Zickus Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/1336761675-24296-4-git-send-email-dzickus@redhat.com Signed-off-by: Ingo Molnar --- arch/x86/kernel/smp.c | 12 ++++-------- 1 file changed, 4 insertions(+), 8 deletions(-) (limited to 'arch/x86/kernel/smp.c') diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c index 228e7405511a..48d2b7ded422 100644 --- a/arch/x86/kernel/smp.c +++ b/arch/x86/kernel/smp.c @@ -110,6 +110,7 @@ */ static atomic_t stopping_cpu = ATOMIC_INIT(-1); +static bool smp_no_nmi_ipi = false; /* * this function sends a 'reschedule' IPI to another CPU. @@ -216,7 +217,7 @@ static void native_stop_other_cpus(int wait) } /* if the REBOOT_VECTOR didn't work, try with the NMI */ - if ((num_online_cpus() > 1)) { + if ((num_online_cpus() > 1) && (!smp_no_nmi_ipi)) { if (register_nmi_handler(NMI_LOCAL, smp_stop_nmi_callback, NMI_FLAG_FIRST, "smp_stop")) /* Note: we ignore failures here */ @@ -245,11 +246,6 @@ finish: local_irq_restore(flags); } -static void native_smp_disable_nmi_ipi(void) -{ - smp_ops.stop_other_cpus = native_irq_stop_other_cpus; -} - /* * Reschedule call back. */ @@ -283,8 +279,8 @@ void smp_call_function_single_interrupt(struct pt_regs *regs) static int __init nonmi_ipi_setup(char *str) { - native_smp_disable_nmi_ipi(); - return 1; + smp_no_nmi_ipi = true; + return 1; } __setup("nonmi_ipi", nonmi_ipi_setup); -- cgit v1.2.3