From: Vlastimil Babka <vbabka@xxxxxxx>
Subject: mm: munlock: fix deadlock in __munlock_pagevec()
Commit 7225522bb ("mm: munlock: batch non-THP page isolation and
munlock+putback using pagevec" introduced __munlock_pagevec() to speed up
munlock by holding lru_lock over multiple isolated pages. Pages that fail
to be isolated are put_page()d immediately, also within the lock.
This can lead to deadlock when __munlock_pagevec() becomes the holder of
the last page pin and put_page() leads to __page_cache_release() which
also locks lru_lock. The deadlock has been observed by Sasha Levin using
trinity.
This patch avoids the deadlock by deferring put_page() operations until
lru_lock is released. Another pagevec (which is also used by later phases
of the function is reused to gather the pages for put_page() operation.
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Reported-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
Cc: Michel Lespinasse <walken@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/mlock.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)
diff -puN mm/mlock.c~mm-munlock-fix-deadlock-in-__munlock_pagevec mm/mlock.c
--- a/mm/mlock.c~mm-munlock-fix-deadlock-in-__munlock_pagevec
+++ a/mm/mlock.c
@@ -298,10 +298,12 @@ static void __munlock_pagevec(struct pag
{
int i;
int nr = pagevec_count(pvec);
- int delta_munlocked = -nr;
+ int delta_munlocked;
struct pagevec pvec_putback;
int pgrescued = 0;
+ pagevec_init(&pvec_putback, 0);
+
/* Phase 1: page isolation */
spin_lock_irq(&zone->lru_lock);
for (i = 0; i < nr; i++) {
@@ -330,18 +332,21 @@ skip_munlock:
/*
* We won't be munlocking this page in the next phase
* but we still need to release the follow_page_mask()
- * pin.
+ * pin. We cannot do it under lru_lock however. If it's
+ * the last pin, __page_cache_release would deadlock.
*/
+ pagevec_add(&pvec_putback, pvec->pages[i]);
pvec->pages[i] = NULL;
- put_page(page);
- delta_munlocked++;
}
}
+ delta_munlocked = -nr + pagevec_count(&pvec_putback);
__mod_zone_page_state(zone, NR_MLOCK, delta_munlocked);
spin_unlock_irq(&zone->lru_lock);
+ /* Now we can release pins of pages that we are not munlocking */
+ pagevec_release(&pvec_putback);
+
/* Phase 2: page munlock */
- pagevec_init(&pvec_putback, 0);
for (i = 0; i < nr; i++) {
struct page *page = pvec->pages[i];
_
--
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