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proc: loadavg reading race

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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@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Michal Schmidt
2008-02-06 01:37:07 -08:00
committed by Linus Torvalds
parent 0a76fe8e50
commit 07a154b2bb
1 changed files with 8 additions and 3 deletions
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11
fs/proc/proc_misc.c
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@@ -84,10 +84,15 @@ static int loadavg_read_proc(char *page, char **start, off_t off,
{ {
int a, b, c; int a, b, c;
int len; 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", len = sprintf(page,"%d.%02d %d.%02d %d.%02d %ld/%d %d\n",
LOAD_INT(a), LOAD_FRAC(a), LOAD_INT(a), LOAD_FRAC(a),
LOAD_INT(b), LOAD_FRAC(b), LOAD_INT(b), LOAD_FRAC(b),