From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx205.postini.com [74.125.245.205]) by kanga.kvack.org (Postfix) with SMTP id DCC2D6B002C for ; Wed, 29 Feb 2012 21:45:27 -0500 (EST) Received: by dald2 with SMTP id d2so187532dal.9 for ; Wed, 29 Feb 2012 18:45:27 -0800 (PST) Date: Wed, 29 Feb 2012 18:44:59 -0800 (PST) From: Hugh Dickins Subject: [PATCH v2 next] memcg: fix deadlock by avoiding stat lock when anon In-Reply-To: Message-ID: References: <20120229193517.GD1673@cmpxchg.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Johannes Weiner , KAMEZAWA Hiroyuki , Konstantin Khlebnikov , linux-kernel@vger.kernel.org, linux-mm@kvack.org Fix deadlock in "memcg: use new logic for page stat accounting". page_remove_rmap() first calls mem_cgroup_begin_update_page_stat(), which may take move_lock_mem_cgroup(), unlocked at the end of page_remove_rmap() by mem_cgroup_end_update_page_stat(). The PageAnon case never needs to mem_cgroup_dec_page_stat(page, MEMCG_NR_FILE_MAPPED); but it often needs to mem_cgroup_uncharge_page(), which does lock_page_cgroup(), while holding that move_lock_mem_cgroup(). Whereas mem_cgroup_move_account() calls move_lock_mem_cgroup() while holding lock_page_cgroup(). Since mem_cgroup_begin and end are unnecessary here for PageAnon, simply avoid the deadlock and wasted calls in that case. Signed-off-by: Hugh Dickins --- v2: added comment in the code so it's not thought just an optimization. mm/rmap.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) --- 3.3-rc5-next/mm/rmap.c 2012-02-26 23:51:46.506050210 -0800 +++ linux/mm/rmap.c 2012-02-29 17:55:42.868665736 -0800 @@ -1166,10 +1166,18 @@ void page_add_file_rmap(struct page *pag */ void page_remove_rmap(struct page *page) { + bool anon = PageAnon(page); bool locked; unsigned long flags; - mem_cgroup_begin_update_page_stat(page, &locked, &flags); + /* + * The anon case has no mem_cgroup page_stat to update; but may + * uncharge_page() below, where the lock ordering can deadlock if + * we hold the lock against page_stat move: so avoid it on anon. + */ + if (!anon) + mem_cgroup_begin_update_page_stat(page, &locked, &flags); + /* page still mapped by someone else? */ if (!atomic_add_negative(-1, &page->_mapcount)) goto out; @@ -1181,7 +1189,7 @@ void page_remove_rmap(struct page *page) * not if it's in swapcache - there might be another pte slot * containing the swap entry, but page not yet written to swap. */ - if ((!PageAnon(page) || PageSwapCache(page)) && + if ((!anon || PageSwapCache(page)) && page_test_and_clear_dirty(page_to_pfn(page), 1)) set_page_dirty(page); /* @@ -1190,7 +1198,7 @@ void page_remove_rmap(struct page *page) */ if (unlikely(PageHuge(page))) goto out; - if (PageAnon(page)) { + if (anon) { mem_cgroup_uncharge_page(page); if (!PageTransHuge(page)) __dec_zone_page_state(page, NR_ANON_PAGES); @@ -1211,7 +1219,8 @@ void page_remove_rmap(struct page *page) * faster for those pages still in swapcache. */ out: - mem_cgroup_end_update_page_stat(page, &locked, &flags); + if (!anon) + mem_cgroup_end_update_page_stat(page, &locked, &flags); } /* -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org