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mm: refactor reinsert of swap_info in sys_swapoff()

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The block within sys_swapoff() which re-inserts the swap_info into the
swap_list in case of failure of try_to_unuse() reads a few values outside
the swap_lock.  While this is safe at that point, it is subtle code.

Simplify the code by moving the reading of these values to a separate
function, refactoring it a bit so they are read from within the swap_lock.
 This is easier to understand, and matches better the way it worked before
I unified the insertion of the swap_info from both sys_swapon and
sys_swapoff.

This change should make no functional difference.  The only real change is
moving the read of two or three structure fields to within the lock
(frontswap_map_get() is nothing more than a read of p->frontswap_map).

Signed-off-by: Cesar Eduardo Barros <cesarb@cesarb.net>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Dan Magenheimer <dan.magenheimer@oracle.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Cesar Eduardo Barros 2012-12-11 16:01:13 -08:00 committed by Linus Torvalds
parent e986850598
commit cf0cac0a09
1 changed files with 17 additions and 9 deletions
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26
mm/swapfile.c
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@ -1443,13 +1443,12 @@ static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
return generic_swapfile_activate(sis, swap_file, span);
}
static void enable_swap_info(struct swap_info_struct *p, int prio,
static void _enable_swap_info(struct swap_info_struct *p, int prio,
unsigned char *swap_map,
unsigned long *frontswap_map)
{
int i, prev;
spin_lock(&swap_lock);
if (prio >= 0)
p->prio = prio;
else
@ -1473,6 +1472,21 @@ static void enable_swap_info(struct swap_info_struct *p, int prio,
else
swap_info[prev]->next = p->type;
frontswap_init(p->type);
}
static void enable_swap_info(struct swap_info_struct *p, int prio,
unsigned char *swap_map,
unsigned long *frontswap_map)
{
spin_lock(&swap_lock);
_enable_swap_info(p, prio, swap_map, frontswap_map);
spin_unlock(&swap_lock);
}
static void reinsert_swap_info(struct swap_info_struct *p)
{
spin_lock(&swap_lock);
_enable_swap_info(p, p->prio, p->swap_map, frontswap_map_get(p));
spin_unlock(&swap_lock);
}
@ -1548,14 +1562,8 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
compare_swap_oom_score_adj(OOM_SCORE_ADJ_MAX, oom_score_adj);
if (err) {
/*
* reading p->prio and p->swap_map outside the lock is
* safe here because only sys_swapon and sys_swapoff
* change them, and there can be no other sys_swapon or
* sys_swapoff for this swap_info_struct at this point.
*/
/* re-insert swap space back into swap_list */
enable_swap_info(p, p->prio, p->swap_map, frontswap_map_get(p));
reinsert_swap_info(p);
goto out_dput;
}