From dcd945e0d8a6d654e3e1de51faea9f98f1504aa5 Mon Sep 17 00:00:00 2001 From: Paul Mackerras Date: Wed, 3 Jun 2009 19:40:36 +1000 Subject: [PATCH] perf_counter: powerpc: Fix race causing "oops trying to read PMC0" errors When using interrupting counters and limited (non-interrupting) counters at the same time, it's possible that we get an interrupt in write_mmcr0() after writing MMCR0 but before we have set up the counters using limited PMCs. What happens then is that we get into perf_counter_interrupt() with counter->hw.idx = 0 for the limited counters, leading to the "oops trying to read PMC0" error message being printed. This fixes the problem by making perf_counter_interrupt() robust against counter->hw.idx being zero (the counter is just ignored in that case) and also by changing write_mmcr0() to write MMCR0 initially with the counter overflow interrupt enable bits masked (set to 0). If the MMCR0 value requested by the caller has either of those bits set, we write MMCR0 again with the requested value of those bits after setting up the limited counters properly. Signed-off-by: Paul Mackerras Cc: Peter Zijlstra Cc: Mike Galbraith Cc: Paul Mackerras Cc: Corey Ashford Cc: Marcelo Tosatti Cc: Arnaldo Carvalho de Melo Cc: Thomas Gleixner Cc: John Kacur Cc: Stephane Eranian LKML-Reference: <18982.17684.138182.954599@cargo.ozlabs.ibm.com> Signed-off-by: Ingo Molnar --- arch/powerpc/kernel/perf_counter.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) diff --git a/arch/powerpc/kernel/perf_counter.c b/arch/powerpc/kernel/perf_counter.c index ea54686..4cc4ac5 100644 --- a/arch/powerpc/kernel/perf_counter.c +++ b/arch/powerpc/kernel/perf_counter.c @@ -372,16 +372,28 @@ static void write_mmcr0(struct cpu_hw_counters *cpuhw, unsigned long mmcr0) /* * Write MMCR0, then read PMC5 and PMC6 immediately. + * To ensure we don't get a performance monitor interrupt + * between writing MMCR0 and freezing/thawing the limited + * counters, we first write MMCR0 with the counter overflow + * interrupt enable bits turned off. */ asm volatile("mtspr %3,%2; mfspr %0,%4; mfspr %1,%5" : "=&r" (pmc5), "=&r" (pmc6) - : "r" (mmcr0), "i" (SPRN_MMCR0), + : "r" (mmcr0 & ~(MMCR0_PMC1CE | MMCR0_PMCjCE)), + "i" (SPRN_MMCR0), "i" (SPRN_PMC5), "i" (SPRN_PMC6)); if (mmcr0 & MMCR0_FC) freeze_limited_counters(cpuhw, pmc5, pmc6); else thaw_limited_counters(cpuhw, pmc5, pmc6); + + /* + * Write the full MMCR0 including the counter overflow interrupt + * enable bits, if necessary. + */ + if (mmcr0 & (MMCR0_PMC1CE | MMCR0_PMCjCE)) + mtspr(SPRN_MMCR0, mmcr0); } /* @@ -1108,7 +1120,7 @@ static void perf_counter_interrupt(struct pt_regs *regs) for (i = 0; i < cpuhw->n_counters; ++i) { counter = cpuhw->counter[i]; - if (is_limited_pmc(counter->hw.idx)) + if (!counter->hw.idx || is_limited_pmc(counter->hw.idx)) continue; val = read_pmc(counter->hw.idx); if ((int)val < 0) { -- 2.7.4