Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit cf0cac0a authored by Cesar Eduardo Barros's avatar Cesar Eduardo Barros Committed by Linus Torvalds
Browse files

mm: refactor reinsert of swap_info in sys_swapoff() 



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: default avatarCesar 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e9868505

mm/swapfile.c

+17 −9
Original line number Diff line number Diff line
@@ -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;

	}