This is a note to let you know that I've just added the patch titled
powerpc/perf: Fix deadlock caused by calling printk() in PMU exception
to the 3.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
powerpc-perf-fix-deadlock-caused-by-calling-printk-in-pmu-exception.patch
and it can be found in the queue-3.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 6772faa1ba22eba18d087c2459030a683b65be57 Mon Sep 17 00:00:00 2001
From: Michael Ellerman <michael@xxxxxxxxxxxxxx>
Date: Wed, 5 Jun 2013 17:58:20 +0000
Subject: powerpc/perf: Fix deadlock caused by calling printk() in PMU exception
From: Michael Ellerman <michael@xxxxxxxxxxxxxx>
commit 6772faa1ba22eba18d087c2459030a683b65be57 upstream.
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@xxxxxxxxxxxxxx>
Signed-off-by: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/powerpc/perf/core-book3s.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -1528,7 +1528,7 @@ static void perf_event_interrupt(struct
}
}
}
- if ((!found) && printk_ratelimit())
+ if (!found && !nmi && printk_ratelimit())
printk(KERN_WARNING "Can't find PMC that caused IRQ\n");
/*
Patches currently in stable-queue which might be from michael@xxxxxxxxxxxxxx are
queue-3.9/powerpc-perf-fix-deadlock-caused-by-calling-printk-in-pmu-exception.patch
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