The patch titled
Subject: mm: refactor reinsert of swap_info in sys_swapoff()
has been added to the -mm tree. Its filename is
mm-refactor-reinsert-of-swap_info-in-sys_swapoff.patch
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From: Cesar Eduardo Barros <cesarb@xxxxxxxxxx>
Subject: 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: Cesar Eduardo Barros <cesarb@xxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/swapfile.c | 26 +++++++++++++++++---------
1 file changed, 17 insertions(+), 9 deletions(-)
diff -puN mm/swapfile.c~mm-refactor-reinsert-of-swap_info-in-sys_swapoff mm/swapfile.c
--- a/mm/swapfile.c~mm-refactor-reinsert-of-swap_info-in-sys_swapoff
+++ a/mm/swapfile.c
@@ -1443,13 +1443,12 @@ static int setup_swap_extents(struct swa
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
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);
}
@@ -1549,14 +1563,8 @@ SYSCALL_DEFINE1(swapoff, const char __us
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;
}
_
Patches currently in -mm which might be from cesarb@xxxxxxxxxx are
linux-next.patch
mm-refactor-reinsert-of-swap_info-in-sys_swapoff.patch
mm-do-not-call-frontswap_init-during-swapoff.patch
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