[tip:perf/core] x86, perf: P4 PMU - fix counters management logic

[tip-bot for Cyrill Gorcunov]

Commit-ID:  1ff3d7d79204612ebe2e611d2592f8898908ca00
Gitweb:     http://git.kernel.org/tip/1ff3d7d79204612ebe2e611d2592f8898908ca00
Author:     Cyrill Gorcunov <gorcunov@xxxxxxxxx>
AuthorDate: Fri, 14 May 2010 23:08:15 +0400
Committer:  Ingo Molnar <mingo@xxxxxxx>
CommitDate: Sat, 15 May 2010 08:38:55 +0200

x86, perf: P4 PMU - fix counters management logic

Jaswinder reported this #GP:

 |
 | Message from syslogd@ht at May 14 09:39:32 ...
 | kernel:[  314.908612] EIP: [<c100ccca>]
 | x86_perf_event_set_period+0x19d/0x1b2 SS:ESP 0068:edac3d70
 |

Ming has narrowed it down to a comparision issue
between arguments with different sizes and
signs. As result event index reached a wrong
value which in turn led to a GP fault.

At the same time it was found that p4_next_cntr
has broken logic and should return the counter
index only if it was not yet borrowed for
another event.

Reported-by: Jaswinder Singh Rajput <jaswinderlinux@xxxxxxxxx>
Reported-by: Lin Ming <ming.m.lin@xxxxxxxxx>
Bisected-by: Lin Ming <ming.m.lin@xxxxxxxxx>
Tested-by: Jaswinder Singh Rajput <jaswinderlinux@xxxxxxxxx>
Signed-off-by: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
CC: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
CC: Frederic Weisbecker <fweisbec@xxxxxxxxx>
LKML-Reference: <20100514190815.GG13509@lenovo>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
 arch/x86/kernel/cpu/perf_event_p4.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event_p4.c b/arch/x86/kernel/cpu/perf_event_p4.c
index cb875b1..424fc8d 100644
--- a/arch/x86/kernel/cpu/perf_event_p4.c
+++ b/arch/x86/kernel/cpu/perf_event_p4.c
@@ -18,7 +18,7 @@
 struct p4_event_bind {
 	unsigned int opcode;			/* Event code and ESCR selector */
 	unsigned int escr_msr[2];		/* ESCR MSR for this event */
-	unsigned char cntr[2][P4_CNTR_LIMIT];	/* counter index (offset), -1 on abscence */
+	char cntr[2][P4_CNTR_LIMIT];		/* counter index (offset), -1 on abscence */
 };
 
 struct p4_cache_event_bind {
@@ -747,11 +747,11 @@ static int p4_get_escr_idx(unsigned int addr)
 static int p4_next_cntr(int thread, unsigned long *used_mask,
 			struct p4_event_bind *bind)
 {
-	int i = 0, j;
+	int i, j;
 
 	for (i = 0; i < P4_CNTR_LIMIT; i++) {
-		j = bind->cntr[thread][i++];
-		if (j == -1 || !test_bit(j, used_mask))
+		j = bind->cntr[thread][i];
+		if (j != -1 && !test_bit(j, used_mask))
 			return j;
 	}
 
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