linux-kernel - [081/205] ARM: 6205/1: perf: ensure counter delta is treated as unsigned

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Message-Id: <20100730175140.967667541@clark.site>
Date:	Fri, 30 Jul 2010 10:51:38 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Jamie Iles <jamie.iles@...ochip.com>,
	Will Deacon <will.deacon@....com>,
	Russell King <rmk+kernel@....linux.org.uk>
Subject: [081/205] ARM: 6205/1: perf: ensure counter delta is treated as unsigned

2.6.34-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Will Deacon <will.deacon@....com>

commit 446a5a8b1eb91a6990e5c8fe29f14e7a95b69132 upstream.

Hardware performance counters on ARM are 32-bits wide but atomic64_t
variables are used to represent counter data in the hw_perf_event structure.

The armpmu_event_update function right-shifts a signed 64-bit delta variable
and adds the result to the event count. This can lead to shifting in sign-bits
if the MSB of the 32-bit counter value is set. This results in perf output
such as:

 Performance counter stats for 'sleep 20':

 18446744073460670464  cycles             <-- 0xFFFFFFFFF12A6000
        7783773  instructions             #      0.000 IPC
            465  context-switches
            161  page-faults
        1172393  branches

   20.154242147  seconds time elapsed

This patch ensures that the delta value is treated as unsigned so that the
right shift sets the upper bits to zero.

Acked-by: Jamie Iles <jamie.iles@...ochip.com>
Signed-off-by: Will Deacon <will.deacon@....com>
Signed-off-by: Russell King <rmk+kernel@....linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 arch/arm/kernel/perf_event.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/arm/kernel/perf_event.c
+++ b/arch/arm/kernel/perf_event.c
@@ -165,7 +165,7 @@ armpmu_event_update(struct perf_event *e
 {
 	int shift = 64 - 32;
 	s64 prev_raw_count, new_raw_count;
-	s64 delta;
+	u64 delta;
 
 again:
 	prev_raw_count = atomic64_read(&hwc->prev_count);


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