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perf_counter: Fix /0 bug in swcounters
author
Peter Zijlstra
<peterz@infradead.org>
Fri, 28 Aug 2009 15:10:47 +0000
(17:10 +0200)
committer
Ingo Molnar
<mingo@elte.hu>
Sat, 29 Aug 2009 11:20:11 +0000
(13:20 +0200)
We have a race in the swcounter stuff where we can start
counting a counter that has never been enabled, this leads to a
/0 situation.
The below avoids the /0 but doesn't close the race, this would
need a new counter state.
The race is due to perf_swcounter_is_counting() which cannot
discern between disabled due to scheduled out, and disabled for
any other reason.
Such a crash has been seen by Ingo:
[ 967.092372] divide error: 0000 [#1] SMP
[ 967.096499] last sysfs file: /sys/devices/system/cpu/cpu15/cache/index2/shared_cpu_map
[ 967.104846] CPU 5
[ 967.106965] Modules linked in:
[ 967.110169] Pid: 3351, comm: hackbench Not tainted 2.6.31-rc8-tip-01158-gd940a54-dirty #1568 X8DTN
[ 967.119456] RIP: 0010:[<
ffffffff810c0aba
>] [<
ffffffff810c0aba
>] perf_swcounter_ctx_event+0x127/0x1af
[ 967.129137] RSP: 0018:
ffff8801a95abd70
EFLAGS:
00010046
[ 967.134699] RAX:
0000000000000002
RBX:
ffff8801bd645c00
RCX:
0000000000000002
[ 967.142162] RDX:
0000000000000000
RSI:
0000000000000000
RDI:
ffff8801bd645d40
[ 967.149584] RBP:
ffff8801a95abdb0
R08:
0000000000000001
R09:
ffff8801a95abe00
[ 967.157042] R10:
0000000000000037
R11:
ffff8801aa1245f8
R12:
ffff8801a95abe00
[ 967.164481] R13:
ffff8801a95abe00
R14:
ffff8801aa1c0e78
R15:
0000000000000001
[ 967.171953] FS:
0000000000000000
(0000) GS:
ffffc90000a00000
(0063) knlGS:
00000000f7f486c0
[ 967.180406] CS: 0010 DS: 002b ES: 002b CR0:
000000008005003b
[ 967.186374] CR2:
000000004822c0ac
CR3:
00000001b19a2000
CR4:
00000000000006e0
[ 967.193770] DR0:
0000000000000000
DR1:
0000000000000000
DR2:
0000000000000000
[ 967.201224] DR3:
0000000000000000
DR6:
00000000ffff0ff0
DR7:
0000000000000400
[ 967.208692] Process hackbench (pid: 3351, threadinfo
ffff8801a95aa000
, task
ffff8801a96b0000
)
[ 967.217607] Stack:
[ 967.219711]
0000000000000000
0000000000000037
0000000200000001
ffffc90000a1107c
[ 967.227296] <0>
ffff8801a95abe00
0000000000000001
0000000000000001
0000000000000037
[ 967.235333] <0>
ffff8801a95abdf0
ffffffff810c0c20
0000000200a14f30
ffff8801a95abe40
[ 967.243532] Call Trace:
[ 967.246103] [<
ffffffff810c0c20
>] do_perf_swcounter_event+0xde/0xec
[ 967.252635] [<
ffffffff810c0ca7
>] perf_tpcounter_event+0x79/0x7b
[ 967.258957] [<
ffffffff81037f73
>] ftrace_profile_sched_switch+0xc0/0xcb
[ 967.265791] [<
ffffffff8155f22d
>] schedule+0x429/0x4c4
[ 967.271156] [<
ffffffff8100c01e
>] int_careful+0xd/0x14
Reported-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <
1251472247
.17617.74.camel@laptop>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
kernel/perf_counter.c
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diff --git
a/kernel/perf_counter.c
b/kernel/perf_counter.c
index
7d4bb83
..
d7cbc57
100644
(file)
--- a/
kernel/perf_counter.c
+++ b/
kernel/perf_counter.c
@@
-4066,6
+4066,7
@@
perf_counter_alloc(struct perf_counter_attr *attr,
hwc->sample_period = attr->sample_period;
if (attr->freq && attr->sample_freq)
hwc->sample_period = 1;
+ hwc->last_period = hwc->sample_period;
atomic64_set(&hwc->period_left, hwc->sample_period);