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Message-Id: <1194873824-29116-1-git-send-email-mschmidt@redhat.com>
Date: Mon, 12 Nov 2007 14:23:44 +0100
From: Michal Schmidt <mschmidt@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: Michal Schmidt <mschmidt@...hat.com>
Subject: [PATCH] proc: loadavg reading race
The avenrun[] values are supposed to be protected by xtime_lock.
loadavg_read_proc does not use it. Theoretically this may result in an
occasional glitch when the value read from /proc/loadavg would be as much as
1<<11 times higher than it should be.
Signed-off-by: Michal Schmidt <mschmidt@...hat.com>
---
fs/proc/proc_misc.c | 11 ++++++++---
1 files changed, 8 insertions(+), 3 deletions(-)
diff --git a/fs/proc/proc_misc.c b/fs/proc/proc_misc.c
index e0d064e..10cc9ad 100644
--- a/fs/proc/proc_misc.c
+++ b/fs/proc/proc_misc.c
@@ -83,10 +83,15 @@ static int loadavg_read_proc(char *page, char **start, off_t off,
{
int a, b, c;
int len;
+ unsigned long seq;
+
+ do {
+ seq = read_seqbegin(&xtime_lock);
+ a = avenrun[0] + (FIXED_1/200);
+ b = avenrun[1] + (FIXED_1/200);
+ c = avenrun[2] + (FIXED_1/200);
+ } while (read_seqretry(&xtime_lock, seq));
- a = avenrun[0] + (FIXED_1/200);
- b = avenrun[1] + (FIXED_1/200);
- c = avenrun[2] + (FIXED_1/200);
len = sprintf(page,"%d.%02d %d.%02d %d.%02d %ld/%d %d\n",
LOAD_INT(a), LOAD_FRAC(a),
LOAD_INT(b), LOAD_FRAC(b),
--
1.5.3.3
-
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