Messages in this thread Patch in this message | | | From | Vlastimil Babka <> | Subject | [PATCH 2/3] mm: munlock: fix deadlock in __munlock_pagevec() | Date | Mon, 16 Dec 2013 11:14:15 +0100 |
| |
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_back() immediately, also within the lock.
This can lead to deadlock when __munlock_pagevec() becomes the holder of the last page pin and put_back() 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_back() 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_back() operation.
Cc: stable@kernel.org Reported-by: Sasha Levin <sasha.levin@oracle.com> Signed-off-by: Vlastimil Babka <vbabka@suse.cz> --- mm/mlock.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-)
diff --git a/mm/mlock.c b/mm/mlock.c index 3847b13..31383d5 100644 --- a/mm/mlock.c +++ b/mm/mlock.c @@ -295,10 +295,12 @@ 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++) { @@ -327,16 +329,22 @@ 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 */ + for (i = 0; i < pagevec_count(&pvec_putback); i++) { + put_page(pvec_putback.pages[i]); + } + /* Phase 2: page munlock */ pagevec_init(&pvec_putback, 0); for (i = 0; i < nr; i++) { -- 1.8.4
| |