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authorMichael Ellerman <michael@ellerman.id.au>2013-06-05 17:58:20 (GMT)
committerBenjamin Herrenschmidt <benh@kernel.crashing.org>2013-06-09 22:36:32 (GMT)
commit6772faa1ba22eba18d087c2459030a683b65be57 (patch)
treeed0774c206c10450569dcae97186fb0d212d1f44 /arch/powerpc/perf
parent82a9f16adc12f51c3f8ea59a7c3c120241aff836 (diff)
powerpc/perf: Fix deadlock caused by calling printk() in PMU exception
In commit bc09c21 "Fix finding overflowed PMC in interrupt" we added a printk() to the PMU exception handler. Unfortunately that is not safe. The problem is that the PMU exception may run even when interrupts are soft disabled, aka NMI context. We do this so that we can profile parts of the kernel that have interrupts soft-disabled. But by calling printk() from the exception handler, we can potentially deadlock in the printk code on logbuf_lock, eg: [c00000038ba575c0] c000000000081928 .vprintk_emit+0xa8/0x540 [c00000038ba576a0] c0000000007bcde8 .printk+0x48/0x58 [c00000038ba57710] c000000000076504 .perf_event_interrupt+0x2d4/0x490 [c00000038ba57810] c00000000001f6f8 .performance_monitor_exception+0x48/0x60 [c00000038ba57880] c0000000000032cc performance_monitor_common+0x14c/0x180 --- Exception: f01 (Performance Monitor) at c0000000007b25d4 ._raw_spin_lock_irq +0x64/0xc0 [c00000038ba57bf0] c00000000007ed90 .devkmsg_read+0xd0/0x5a0 [c00000038ba57d00] c0000000001c2934 .vfs_read+0xc4/0x1e0 [c00000038ba57d90] c0000000001c2cd8 .SyS_read+0x58/0xd0 [c00000038ba57e30] c000000000009d54 syscall_exit+0x0/0x98 --- Exception: c01 (System Call) at 00001fffffbf6f7c SP (3ffff6d4de10) is in userspace Fix it by making sure we only call printk() when we are not in NMI context. Signed-off-by: Michael Ellerman <michael@ellerman.id.au> Cc: <stable@vger.kernel.org> # 3.9 Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Diffstat (limited to 'arch/powerpc/perf')
-rw-r--r--arch/powerpc/perf/core-book3s.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index 845c867..29c6482 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -1758,7 +1758,7 @@ static void perf_event_interrupt(struct pt_regs *regs)
}
}
}
- if ((!found) && printk_ratelimit())
+ if (!found && !nmi && printk_ratelimit())
printk(KERN_WARNING "Can't find PMC that caused IRQ\n");
/*

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