From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755836Ab3KEX11 (ORCPT ); Tue, 5 Nov 2013 18:27:27 -0500 Received: from mail-ve0-f201.google.com ([209.85.128.201]:64867 "EHLO mail-ve0-f201.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755462Ab3KEX10 (ORCPT ); Tue, 5 Nov 2013 18:27:26 -0500 From: Sameer Nanda To: akpm@linux-foundation.org, mhocko@suse.cz, rientjes@google.com, hannes@cmpxchg.org, rusty@rustcorp.com.au Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sameer Nanda Subject: [PATCH] mm, oom: Fix race when selecting process to kill Date: Tue, 5 Nov 2013 15:26:27 -0800 Message-Id: <1383693987-14171-1-git-send-email-snanda@chromium.org> X-Mailer: git-send-email 1.8.4.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The selection of the process to be killed happens in two spots -- first in select_bad_process and then a further refinement by looking for child processes in oom_kill_process. Since this is a two step process, it is possible that the process selected by select_bad_process may get a SIGKILL just before oom_kill_process executes. If this were to happen, __unhash_process deletes this process from the thread_group list. This then results in oom_kill_process getting stuck in an infinite loop when traversing the thread_group list of the selected process. Fix this race by holding the tasklist_lock across the calls to both select_bad_process and oom_kill_process. Change-Id: I8f96b106b3257b5c103d6497bac7f04f4dff4e60 Signed-off-by: Sameer Nanda --- mm/oom_kill.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/oom_kill.c b/mm/oom_kill.c index 6738c47..7bd3587 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -436,7 +436,6 @@ void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order, * parent. This attempts to lose the minimal amount of work done while * still freeing memory. */ - read_lock(&tasklist_lock); do { list_for_each_entry(child, &t->children, sibling) { unsigned int child_points; @@ -456,7 +455,6 @@ void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order, } } } while_each_thread(p, t); - read_unlock(&tasklist_lock); rcu_read_lock(); p = find_lock_task_mm(victim); @@ -641,6 +639,7 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, mpol_mask = (constraint == CONSTRAINT_MEMORY_POLICY) ? nodemask : NULL; check_panic_on_oom(constraint, gfp_mask, order, mpol_mask); + read_lock(&tasklist_lock); if (sysctl_oom_kill_allocating_task && current->mm && !oom_unkillable_task(current, NULL, nodemask) && current->signal->oom_score_adj != OOM_SCORE_ADJ_MIN) { @@ -663,6 +662,7 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, killed = 1; } out: + read_unlock(&tasklist_lock); /* * Give the killed threads a good chance of exiting before trying to * allocate memory again. -- 1.8.4.1