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powerpc/perf_event: Fix oops due to perf_event_do_pending call

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Anton Blanchard found that large POWER systems would occasionally
crash in the exception exit path when profiling with perf_events.
The symptom was that an interrupt would occur late in the exit path
when the MSR[RI] (recoverable interrupt) bit was clear.  Interrupts
should be hard-disabled at this point but they were enabled.  Because
the interrupt was not recoverable the system panicked.

The reason is that the exception exit path was calling
perf_event_do_pending after hard-disabling interrupts, and
perf_event_do_pending will re-enable interrupts.

The simplest and cleanest fix for this is to use the same mechanism
that 32-bit powerpc does, namely to cause a self-IPI by setting the
decrementer to 1.  This means we can remove the tests in the exception
exit path and raw_local_irq_restore.

This also makes sure that the call to perf_event_do_pending from
timer_interrupt() happens within irq_enter/irq_exit.  (Note that
calling perf_event_do_pending from timer_interrupt does not mean that
there is a possible 1/HZ latency; setting the decrementer to 1 ensures
that the timer interrupt will happen immediately, i.e. within one
timebase tick, which is a few nanoseconds or 10s of nanoseconds.)

Signed-off-by: Paul Mackerras <paulus@samba.org>
Cc: stable@kernel.org
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Paul Mackerras
2010-04-13 20:46:04 +00:00
committed by Benjamin Herrenschmidt
parent cea0d767c2
commit 0fe1ac48be
5 changed files with 48 additions and 66 deletions
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38
arch/powerpc/include/asm/hw_irq.h
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@ -130,43 +130,5 @@ static inline int irqs_disabled_flags(unsigned long flags)
*/
struct irq_chip;
#ifdef CONFIG_PERF_EVENTS
#ifdef CONFIG_PPC64
static inline unsigned long test_perf_event_pending(void)
{
unsigned long x;
asm volatile("lbz %0,%1(13)"
: "=r" (x)
: "i" (offsetof(struct paca_struct, perf_event_pending)));
return x;
}
static inline void set_perf_event_pending(void)
{
asm volatile("stb %0,%1(13)" : :
"r" (1),
"i" (offsetof(struct paca_struct, perf_event_pending)));
}
static inline void clear_perf_event_pending(void)
{
asm volatile("stb %0,%1(13)" : :
"r" (0),
"i" (offsetof(struct paca_struct, perf_event_pending)));
}
#endif /* CONFIG_PPC64 */
#else /* CONFIG_PERF_EVENTS */
static inline unsigned long test_perf_event_pending(void)
{
return 0;
}
static inline void clear_perf_event_pending(void) {}
#endif /* CONFIG_PERF_EVENTS */
#endif /* __KERNEL__ */
#endif /* _ASM_POWERPC_HW_IRQ_H */