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x86: Avoid calling arch_trigger_all_cpu_backtrace() at the same time

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The spin_lock_debug/rcu_cpu_stall detector uses
trigger_all_cpu_backtrace() to dump cpu backtrace.
Therefore it is possible that trigger_all_cpu_backtrace()
could be called at the same time on different CPUs, which
triggers and 'unknown reason NMI' warning. The following case
illustrates the problem:

      CPU1                    CPU2                     ...   CPU N
                       trigger_all_cpu_backtrace()
                       set "backtrace_mask" to cpu mask
                               |
generate NMI interrupts  generate NMI interrupts       ...
    \                          |                               /
     \                         |                              /

The "backtrace_mask" will be cleaned by the first NMI interrupt
at nmi_watchdog_tick(), then the following NMI interrupts
generated by other cpus's arch_trigger_all_cpu_backtrace() will
be taken as unknown reason NMI interrupts.

This patch uses a test_and_set to avoid the problem, and stop
the arch_trigger_all_cpu_backtrace() from calling to avoid
dumping a double cpu backtrace info when there is already a
trigger_all_cpu_backtrace() in progress.

Signed-off-by: Dongdong Deng <dongdong.deng@windriver.com>
Reviewed-by: Bruce Ashfield <bruce.ashfield@windriver.com>
Cc: fweisbec@gmail.com
LKML-Reference: <1294198689-15447-2-git-send-email-dzickus@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Don Zickus <dzickus@redhat.com>
This commit is contained in:
Dongdong Deng 2011-01-04 22:38:08 -05:00 committed by Ingo Molnar
parent 9ab181fa9f
commit 554ec06398
1 changed files with 13 additions and 0 deletions
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13
arch/x86/kernel/apic/hw_nmi.c
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@ -28,10 +28,20 @@ u64 hw_nmi_get_sample_period(void)
/* For reliability, we're prepared to waste bits here. */
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)
{
int i;
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.
*/
return;
cpumask_copy(to_cpumask(backtrace_mask), cpu_online_mask);
printk(KERN_INFO "sending NMI to all CPUs:\n");
@ -43,6 +53,9 @@ void arch_trigger_all_cpu_backtrace(void)
break;
mdelay(1);
}
clear_bit(0, &backtrace_flag);
smp_mb__after_clear_bit();
}
static int __kprobes