Commit 3b25df93 authored Jan 02, 2014 by Vlastimil Babka Committed by Linus Torvalds Jan 02, 2014

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: Vlastimil Babka <vbabka@suse.cz>
Reported-by: Sasha 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus 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 @@ 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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