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@gmail.com>
Reported-by: Lin Ming <ming.m.lin@intel.com>
Bisected-by: Lin Ming <ming.m.lin@intel.com>
Tested-by: Jaswinder Singh Rajput <jaswinderlinux@gmail.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <20100514190815.GG13509@lenovo>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

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 cb875b1e2e87..424fc8de68e4 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;
         }