From: Nico Pache <npache@xxxxxxxxxx>
Subject: oom_kill.c: futex: delay the OOM reaper to allow time for proper futex cleanup
The pthread struct is allocated on PRIVATE|ANONYMOUS memory [1] which can
be targeted by the oom reaper. This mapping is used to store the futex
robust list head; the kernel does not keep a copy of the robust list and
instead references a userspace address to maintain the robustness during a
process death. A race can occur between exit_mm and the oom reaper that
allows the oom reaper to free the memory of the futex robust list before
the exit path has handled the futex death:
CPU1 CPU2
------------------------------------------------------------------------
page_fault
do_exit "signal"
wake_oom_reaper
oom_reaper
oom_reap_task_mm (invalidates mm)
exit_mm
exit_mm_release
futex_exit_release
futex_cleanup
exit_robust_list
get_user (EFAULT- can't access memory)
If the get_user EFAULT's, the kernel will be unable to recover the waiters
on the robust_list, leaving userspace mutexes hung indefinitely.
Delay the OOM reaper, allowing more time for the exit path to perform the
futex cleanup.
Reproducer: https://gitlab.com/jsavitz/oom_futex_reproducer
Based on a patch by Michal Hocko.
[1] https://elixir.bootlin.com/glibc/glibc-2.35/source/nptl/allocatestack.c#L370
Link: https://lkml.kernel.org/r/20220414144042.677008-1-npache@xxxxxxxxxx
Fixes: 212925802454 ("mm: oom: let oom_reap_task and exit_mmap run concurrently")
Signed-off-by: Joel Savitz <jsavitz@xxxxxxxxxx>
Signed-off-by: Nico Pache <npache@xxxxxxxxxx>
Co-developed-by: Joel Savitz <jsavitz@xxxxxxxxxx>
Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Rafael Aquini <aquini@xxxxxxxxxx>
Cc: Waiman Long <longman@xxxxxxxxxx>
Cc: Herton R. Krzesinski <herton@xxxxxxxxxx>
Cc: Juri Lelli <juri.lelli@xxxxxxxxxx>
Cc: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Cc: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Ben Segall <bsegall@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Joel Savitz <jsavitz@xxxxxxxxxx>
Cc: Darren Hart <dvhart@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/sched.h | 1
mm/oom_kill.c | 54 +++++++++++++++++++++++++++++-----------
2 files changed, 41 insertions(+), 14 deletions(-)
--- a/include/linux/sched.h~oom_killc-futex-delay-the-oom-reaper-to-allow-time-for-proper-futex-cleanup
+++ a/include/linux/sched.h
@@ -1443,6 +1443,7 @@ struct task_struct {
int pagefault_disabled;
#ifdef CONFIG_MMU
struct task_struct *oom_reaper_list;
+ struct timer_list oom_reaper_timer;
#endif
#ifdef CONFIG_VMAP_STACK
struct vm_struct *stack_vm_area;
--- a/mm/oom_kill.c~oom_killc-futex-delay-the-oom-reaper-to-allow-time-for-proper-futex-cleanup
+++ a/mm/oom_kill.c
@@ -632,7 +632,7 @@ done:
*/
set_bit(MMF_OOM_SKIP, &mm->flags);
- /* Drop a reference taken by wake_oom_reaper */
+ /* Drop a reference taken by queue_oom_reaper */
put_task_struct(tsk);
}
@@ -644,12 +644,12 @@ static int oom_reaper(void *unused)
struct task_struct *tsk = NULL;
wait_event_freezable(oom_reaper_wait, oom_reaper_list != NULL);
- spin_lock(&oom_reaper_lock);
+ spin_lock_irq(&oom_reaper_lock);
if (oom_reaper_list != NULL) {
tsk = oom_reaper_list;
oom_reaper_list = tsk->oom_reaper_list;
}
- spin_unlock(&oom_reaper_lock);
+ spin_unlock_irq(&oom_reaper_lock);
if (tsk)
oom_reap_task(tsk);
@@ -658,22 +658,48 @@ static int oom_reaper(void *unused)
return 0;
}
-static void wake_oom_reaper(struct task_struct *tsk)
+static void wake_oom_reaper(struct timer_list *timer)
{
- /* mm is already queued? */
- if (test_and_set_bit(MMF_OOM_REAP_QUEUED, &tsk->signal->oom_mm->flags))
+ struct task_struct *tsk = container_of(timer, struct task_struct,
+ oom_reaper_timer);
+ struct mm_struct *mm = tsk->signal->oom_mm;
+ unsigned long flags;
+
+ /* The victim managed to terminate on its own - see exit_mmap */
+ if (test_bit(MMF_OOM_SKIP, &mm->flags)) {
+ put_task_struct(tsk);
return;
+ }
- get_task_struct(tsk);
-
- spin_lock(&oom_reaper_lock);
+ spin_lock_irqsave(&oom_reaper_lock, flags);
tsk->oom_reaper_list = oom_reaper_list;
oom_reaper_list = tsk;
- spin_unlock(&oom_reaper_lock);
+ spin_unlock_irqrestore(&oom_reaper_lock, flags);
trace_wake_reaper(tsk->pid);
wake_up(&oom_reaper_wait);
}
+/*
+ * Give the OOM victim time to exit naturally before invoking the oom_reaping.
+ * The timers timeout is arbitrary... the longer it is, the longer the worst
+ * case scenario for the OOM can take. If it is too small, the oom_reaper can
+ * get in the way and release resources needed by the process exit path.
+ * e.g. The futex robust list can sit in Anon|Private memory that gets reaped
+ * before the exit path is able to wake the futex waiters.
+ */
+#define OOM_REAPER_DELAY (2*HZ)
+static void queue_oom_reaper(struct task_struct *tsk)
+{
+ /* mm is already queued? */
+ if (test_and_set_bit(MMF_OOM_REAP_QUEUED, &tsk->signal->oom_mm->flags))
+ return;
+
+ get_task_struct(tsk);
+ timer_setup(&tsk->oom_reaper_timer, wake_oom_reaper, 0);
+ tsk->oom_reaper_timer.expires = jiffies + OOM_REAPER_DELAY;
+ add_timer(&tsk->oom_reaper_timer);
+}
+
static int __init oom_init(void)
{
oom_reaper_th = kthread_run(oom_reaper, NULL, "oom_reaper");
@@ -681,7 +707,7 @@ static int __init oom_init(void)
}
subsys_initcall(oom_init)
#else
-static inline void wake_oom_reaper(struct task_struct *tsk)
+static inline void queue_oom_reaper(struct task_struct *tsk)
{
}
#endif /* CONFIG_MMU */
@@ -932,7 +958,7 @@ static void __oom_kill_process(struct ta
rcu_read_unlock();
if (can_oom_reap)
- wake_oom_reaper(victim);
+ queue_oom_reaper(victim);
mmdrop(mm);
put_task_struct(victim);
@@ -968,7 +994,7 @@ static void oom_kill_process(struct oom_
task_lock(victim);
if (task_will_free_mem(victim)) {
mark_oom_victim(victim);
- wake_oom_reaper(victim);
+ queue_oom_reaper(victim);
task_unlock(victim);
put_task_struct(victim);
return;
@@ -1067,7 +1093,7 @@ bool out_of_memory(struct oom_control *o
*/
if (task_will_free_mem(current)) {
mark_oom_victim(current);
- wake_oom_reaper(current);
+ queue_oom_reaper(current);
return true;
}
_
