linux-hardened/mm/thrash.c
Mika Kukkonen 7faaa5f0bf Bug in mm/thrash.c function grab_swap_token()
Following bug was uncovered by compiling with '-W' flag:

  CC      mm/thrash.o
mm/thrash.c: In function ‘grab_swap_token’:
mm/thrash.c:52: warning: comparison of unsigned expression < 0 is always false

Variable token_priority is unsigned, so decrementing first and then
checking the result does not work; fixed by reversing the test, patch
attached (compile tested only).

I am not sure if likely() makes much sense in this new situation, but
I'll let somebody else to make a decision on that.

Signed-off-by: Mika Kukkonen <mikukkon@iki.fi>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 08:29:32 -07:00

79 lines
2 KiB
C

/*
* mm/thrash.c
*
* Copyright (C) 2004, Red Hat, Inc.
* Copyright (C) 2004, Rik van Riel <riel@redhat.com>
* Released under the GPL, see the file COPYING for details.
*
* Simple token based thrashing protection, using the algorithm
* described in: http://www.cs.wm.edu/~sjiang/token.pdf
*
* Sep 2006, Ashwin Chaugule <ashwin.chaugule@celunite.com>
* Improved algorithm to pass token:
* Each task has a priority which is incremented if it contended
* for the token in an interval less than its previous attempt.
* If the token is acquired, that task's priority is boosted to prevent
* the token from bouncing around too often and to let the task make
* some progress in its execution.
*/
#include <linux/jiffies.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/swap.h>
static DEFINE_SPINLOCK(swap_token_lock);
struct mm_struct *swap_token_mm;
static unsigned int global_faults;
void grab_swap_token(void)
{
int current_interval;
global_faults++;
current_interval = global_faults - current->mm->faultstamp;
if (!spin_trylock(&swap_token_lock))
return;
/* First come first served */
if (swap_token_mm == NULL) {
current->mm->token_priority = current->mm->token_priority + 2;
swap_token_mm = current->mm;
goto out;
}
if (current->mm != swap_token_mm) {
if (current_interval < current->mm->last_interval)
current->mm->token_priority++;
else {
if (likely(current->mm->token_priority > 0))
current->mm->token_priority--;
}
/* Check if we deserve the token */
if (current->mm->token_priority >
swap_token_mm->token_priority) {
current->mm->token_priority += 2;
swap_token_mm = current->mm;
}
} else {
/* Token holder came in again! */
current->mm->token_priority += 2;
}
out:
current->mm->faultstamp = global_faults;
current->mm->last_interval = current_interval;
spin_unlock(&swap_token_lock);
return;
}
/* Called on process exit. */
void __put_swap_token(struct mm_struct *mm)
{
spin_lock(&swap_token_lock);
if (likely(mm == swap_token_mm))
swap_token_mm = NULL;
spin_unlock(&swap_token_lock);
}