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linux/arch/powerpc/perf
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Michael Ellerman 6772faa1ba 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>
2013-06-10 08:36:32 +10:00
..
bhrb.S powerpc/perf: Add basic assembly code to read BHRB entries on POWER8 2013-04-26 16:11:11 +10:00
callchain.c powerpc/perf: Use perf_instruction_pointer in callchains 2012-07-10 19:18:46 +10:00
core-book3s.c powerpc/perf: Fix deadlock caused by calling printk() in PMU exception 2013-06-10 08:36:32 +10:00
core-fsl-emb.c perf: Pass last sampling period to perf_sample_data_init() 2012-05-09 15:23:12 +02:00
e500-pmu.c powerpc/perf: Add stalled-cycles events 2013-01-10 17:00:56 +11:00
Makefile powerpc/perf: Add basic assembly code to read BHRB entries on POWER8 2013-04-26 16:11:11 +10:00
mpc7450-pmu.c
power4-pmu.c powerpc/perf: Fix instruction address sampling on 970 and Power4 2012-03-28 11:33:24 +11:00
power5-pmu.c powerpc/perf: Add an explict flag indicating presence of SLOT field 2013-04-26 16:11:07 +10:00
power5+-pmu.c powerpc/perf: Add an explict flag indicating presence of SLOT field 2013-04-26 16:11:07 +10:00
power6-pmu.c
power7-pmu.c perf/POWER7: Create a sysfs format entry for Power7 events 2013-03-13 17:01:04 -03:00
power8-pmu.c powerpc/perf: Define BHRB generic functions, data and flags for POWER8 2013-04-26 16:13:01 +10:00
ppc970-pmu.c powerpc/perf: Fix instruction address sampling on 970 and Power4 2012-03-28 11:33:24 +11:00