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| author | Peter Zijlstra <peterz@infradead.org> | 2009-08-28 17:10:47 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2009-08-29 13:20:11 +0200 |
| commit | eced1dfcfcf6b0a35e925d73916a9d8e36ab5457 (patch) | |
| tree | a709c2d32788f91aa07e03c9b01bafae15f923f3 /kernel | |
| parent | 6bb56347f5162d1a7cb1dc461023360781ecd4c0 (diff) | |
| download | linux-eced1dfcfcf6b0a35e925d73916a9d8e36ab5457.tar.gz linux-eced1dfcfcf6b0a35e925d73916a9d8e36ab5457.tar.bz2 linux-eced1dfcfcf6b0a35e925d73916a9d8e36ab5457.zip | |
perf_counter: Fix /0 bug in swcounters
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>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/perf_counter.c | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c index 7d4bb83b78cf..d7cbc579fc80 100644 --- 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); |