A small userland program I wrote to assist me in drive forensic operations soft deadlocked on Linux 3.14.4. The stack trace from /proc was: [<ffffffff8112968e>] sleep_on_page_killable+0xe/0x40 [<ffffffff81129829>] wait_on_page_bit_killable+0x79/0x80 [<ffffffff811299a5>] __lock_page_or_retry+0x95/0xc0 [<ffffffff8112a95b>] filemap_fault+0x21b/0x420 [<ffffffff8115685e>] __do_fault+0x6e/0x520 [<ffffffff81156de3>] handle_pte_fault+0xd3/0x1f0 [<ffffffff81157073>] __handle_mm_fault+0x173/0x290 [<ffffffff811571d2>] handle_mm_fault+0x42/0xb0 [<ffffffff81587a11>] __do_page_fault+0x191/0x490 [<ffffffff81587dec>] do_page_fault+0xc/0x10 [<ffffffff81584622>] page_fault+0x22/0x30 [<ffffffffffffffff>] 0xffffffffffffffff The program used mmap() to do a linear scan of the device on 64-bit hardware. The block device in question was 200GB in size and the system had only 8GB of RAM. All IO operations stopped following pageout. shrink_page_list() seemed to have raced with filemap_fault() by evicting a page when we had an active fault handler. This is possible only because 02c6de8d757cb32c0829a45d81c3dfcbcafd998b altered the behavior of shrink_page_list() to ignore references. Consequently, we must call unlock_page() instead of __clear_page_locked() when doing this so that waiters are notified. unlock_page() here will cause active page fault handlers to retry (depending on the architecture), which avoids the soft deadlock. Signed-off-by: Richard Yao <ryao@xxxxxxxxxx> --- mm/vmscan.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 3f56c8d..c07c635 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1083,13 +1083,16 @@ static unsigned long shrink_page_list(struct list_head *page_list, goto keep_locked; /* - * At this point, we have no other references and there is - * no way to pick any more up (removed from LRU, removed - * from pagecache). Can use non-atomic bitops now (and + * Unless we force reclaim, we have no other references and + * there is no way to pick any more up (removed from LRU, + * removed from pagecache). Can use non-atomic bitops now (and * we obviously don't have to worry about waking up a process * waiting on the page lock, because there are no references. */ - __clear_page_locked(page); + if (force_reclaim) + unlock_page(page); + else + __clear_page_locked(page); free_it: nr_reclaimed++; -- 1.8.3.2 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>