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mm: munlock: fix deadlock in __munlock_pagevec()

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Commit 7225522bb4 ("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 <[email protected]>
Reported-by: Sasha Levin <[email protected]>
Cc: Michel Lespinasse <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Vlastimil Babka 2014-01-02 12:58:44 -08:00 • committed by Linus Torvalds
commit 3b25df93c6
1 changed files with 10 additions and 5 deletions
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15
mm/mlock.c
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@ -298,10 +298,12 @@ static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone)
{
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];