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Commit 3b25df93 authored by Vlastimil Babka's avatar Vlastimil Babka Committed by Linus Torvalds
Browse files

mm: munlock: fix deadlock in __munlock_pagevec() 



Commit 7225522b ("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: default avatarVlastimil Babka <vbabka@suse.cz>
Reported-by: default avatarSasha Levin <sasha.levin@oracle.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent c424be1c

mm/mlock.c

+10 −5
Original line number Diff line number Diff line
@@ -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 @@ static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone) 
			/*

			 * 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];