lkml.org 
[lkml]   [2013]   [Nov]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v3] mm, oom: Fix race when selecting process to kill
Date
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 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 adding a pid_alive check for the selected process
with tasklist_lock held in oom_kill_process.

Signed-off-by: Sameer Nanda <snanda@chromium.org>
---
mm/oom_kill.c | 21 ++++++++++++++++++---
1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 6738c47..7b28d9f 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -413,12 +413,20 @@ void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
DEFAULT_RATELIMIT_BURST);

/*
+ * while_each_thread is currently not RCU safe. Lets hold the
+ * tasklist_lock across all invocations of while_each_thread (including
+ * the one in find_lock_task_mm) in this function.
+ */
+ read_lock(&tasklist_lock);
+
+ /*
* If the task is already exiting, don't alarm the sysadmin or kill
* its children or threads, just set TIF_MEMDIE so it can die quickly
*/
- if (p->flags & PF_EXITING) {
+ if (p->flags & PF_EXITING || !pid_alive(p)) {
set_tsk_thread_flag(p, TIF_MEMDIE);
put_task_struct(p);
+ read_unlock(&tasklist_lock);
return;
}

@@ -436,7 +444,6 @@ 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;
@@ -456,10 +463,18 @@ 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);
+
+ /*
+ * Since while_each_thread is currently not RCU safe, this unlock of
+ * tasklist_lock may need to be moved further down if any additional
+ * while_each_thread loops get added to this function.
+ */
+ read_unlock(&tasklist_lock);
+
if (!p) {
rcu_read_unlock();
put_task_struct(victim);
--
1.8.4.1


\
 
 \ /
  Last update: 2013-11-08 21:41    [W:0.165 / U:0.036 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site