nmi: provide the option to issue an NMI back trace to every cpu but current

Sometimes it is preferred not to use the trigger_all_cpu_backtrace()
routine when one wants to avoid capturing a back trace for current.  For
instance if one was previously captured recently.

This patch provides a new routine namely
trigger_allbutself_cpu_backtrace() which offers the flexibility to issue
an NMI to every cpu but current and capture a back trace accordingly.

Patch x86 and sparc to support new routine.

[dzickus@redhat.com: add stub in #else clause]
[dzickus@redhat.com: don't print message in single processor case, wrap with get/put_cpu based on Oleg's suggestion]
[sfr@canb.auug.org.au: undo C99ism]
Signed-off-by: Aaron Tomlin <atomlin@redhat.com>
Signed-off-by: Don Zickus <dzickus@redhat.com>
Acked-by: David S. Miller <davem@davemloft.net>
Cc: Mateusz Guzik <mguzik@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

5 files changed, 38 insertions, 13 deletions

diff --git a/arch/sparc/include/asm/irq_64.h b/arch/sparc/include/asm/irq_64.h
index 375cffcf7dbd..91d219381306 100644
--- a/arch/sparc/include/asm/irq_64.h
+++ b/arch/sparc/include/asm/irq_64.h
@@ -89,7 +89,7 @@ static inline unsigned long get_softint(void)
         return retval;
 }
 
-void arch_trigger_all_cpu_backtrace(void);
+void arch_trigger_all_cpu_backtrace(bool);
 #define arch_trigger_all_cpu_backtrace arch_trigger_all_cpu_backtrace
 
 extern void *hardirq_stack[NR_CPUS];
diff --git a/arch/sparc/kernel/process_64.c b/arch/sparc/kernel/process_64.c
index b2988f25e230..027e09986194 100644
--- a/arch/sparc/kernel/process_64.c
+++ b/arch/sparc/kernel/process_64.c
@@ -239,7 +239,7 @@ static void __global_reg_poll(struct global_reg_snapshot *gp)
         }
 }
 
-void arch_trigger_all_cpu_backtrace(void)
+void arch_trigger_all_cpu_backtrace(bool include_self)
 {
         struct thread_info *tp = current_thread_info();
         struct pt_regs *regs = get_irq_regs();
@@ -251,16 +251,22 @@ void arch_trigger_all_cpu_backtrace(void)
 
         spin_lock_irqsave(&global_cpu_snapshot_lock, flags);
 
-        memset(global_cpu_snapshot, 0, sizeof(global_cpu_snapshot));
-
         this_cpu = raw_smp_processor_id();
 
-        __global_reg_self(tp, regs, this_cpu);
+        memset(global_cpu_snapshot, 0, sizeof(global_cpu_snapshot));
+
+        if (include_self)
+                __global_reg_self(tp, regs, this_cpu);
 
         smp_fetch_global_regs();
 
         for_each_online_cpu(cpu) {
-                struct global_reg_snapshot *gp = &global_cpu_snapshot[cpu].reg;
+                struct global_reg_snapshot *gp;
+
+                if (!include_self && cpu == this_cpu)
+                        continue;
+
+                gp = &global_cpu_snapshot[cpu].reg;
 
                 __global_reg_poll(gp);
 
@@ -292,7 +298,7 @@ void arch_trigger_all_cpu_backtrace(void)
 
 static void sysrq_handle_globreg(int key)
 {
-        arch_trigger_all_cpu_backtrace();
+        arch_trigger_all_cpu_backtrace(true);
 }
 
 static struct sysrq_key_op sparc_globalreg_op = {
diff --git a/arch/x86/include/asm/irq.h b/arch/x86/include/asm/irq.h
index cb6cfcd034cf..a80cbb88ea91 100644
--- a/arch/x86/include/asm/irq.h
+++ b/arch/x86/include/asm/irq.h
@@ -43,7 +43,7 @@ extern int vector_used_by_percpu_irq(unsigned int vector);
 extern void init_ISA_irqs(void);
 
 #ifdef CONFIG_X86_LOCAL_APIC
-void arch_trigger_all_cpu_backtrace(void);
+void arch_trigger_all_cpu_backtrace(bool);
 #define arch_trigger_all_cpu_backtrace arch_trigger_all_cpu_backtrace
 #endif
 
diff --git a/arch/x86/kernel/apic/hw_nmi.c b/arch/x86/kernel/apic/hw_nmi.c
index c3fcb5de5083..6a1e71bde323 100644
--- a/arch/x86/kernel/apic/hw_nmi.c
+++ b/arch/x86/kernel/apic/hw_nmi.c
@@ -33,31 +33,41 @@ static DECLARE_BITMAP(backtrace_mask, NR_CPUS) __read_mostly;
 /* "in progress" flag of arch_trigger_all_cpu_backtrace */
 static unsigned long backtrace_flag;
 
-void arch_trigger_all_cpu_backtrace(void)
+void arch_trigger_all_cpu_backtrace(bool include_self)
 {
         int i;
+        int cpu = get_cpu();
 
-        if (test_and_set_bit(0, &backtrace_flag))
+        if (test_and_set_bit(0, &backtrace_flag)) {
                 /*
                  * If there is already a trigger_all_cpu_backtrace() in progress
                  * (backtrace_flag == 1), don't output double cpu dump infos.
                  */
+                put_cpu();
                 return;
+        }
 
         cpumask_copy(to_cpumask(backtrace_mask), cpu_online_mask);
+        if (!include_self)
+                cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
 
-        printk(KERN_INFO "sending NMI to all CPUs:\n");
-        apic->send_IPI_all(NMI_VECTOR);
+        if (!cpumask_empty(to_cpumask(backtrace_mask))) {
+                pr_info("sending NMI to %s CPUs:\n",
+                        (include_self ? "all" : "other"));
+                apic->send_IPI_mask(to_cpumask(backtrace_mask), NMI_VECTOR);
+        }
 
         /* Wait for up to 10 seconds for all CPUs to do the backtrace */
         for (i = 0; i < 10 * 1000; i++) {
                 if (cpumask_empty(to_cpumask(backtrace_mask)))
                         break;
                 mdelay(1);
+                touch_softlockup_watchdog();
         }
 
         clear_bit(0, &backtrace_flag);
         smp_mb__after_atomic();
+        put_cpu();
 }
 
 static int
diff --git a/include/linux/nmi.h b/include/linux/nmi.h
index 6a45fb583ff1..a17ab6398d7c 100644
--- a/include/linux/nmi.h
+++ b/include/linux/nmi.h
@@ -32,15 +32,24 @@ static inline void touch_nmi_watchdog(void)
 #ifdef arch_trigger_all_cpu_backtrace
 static inline bool trigger_all_cpu_backtrace(void)
 {
-        arch_trigger_all_cpu_backtrace();
+        arch_trigger_all_cpu_backtrace(true);
 
         return true;
 }
+static inline bool trigger_allbutself_cpu_backtrace(void)
+{
+        arch_trigger_all_cpu_backtrace(false);
+        return true;
+}
 #else
 static inline bool trigger_all_cpu_backtrace(void)
 {
         return false;
 }
+static inline bool trigger_allbutself_cpu_backtrace(void)
+{
+        return false;
+}
 #endif
 
 #ifdef CONFIG_LOCKUP_DETECTOR