When I was examining a bug which occurs under CPU + memory pressure, I
observed that a thread which called out_of_memory() can sleep for minutes
at schedule_timeout_killable(1) with oom_lock held when many threads are
doing direct reclaim.
The whole point of the sleep is give the OOM victim some time to exit.
But since commit 27ae357fa82be5ab ("mm, oom: fix concurrent munlock and
oom reaper unmap, v3") changed the OOM victim to wait for oom_lock in order
to close race window at exit_mmap(), the whole point of this sleep is lost
now. We need to make sure that the thread which called out_of_memory() will
release oom_lock shortly. Therefore, this patch brings the sleep to outside
of the OOM path. Whether it is safe to remove the sleep will be tested by
future patch.
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: Roman Gushchin <guro@xxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
---
mm/oom_kill.c | 38 +++++++++++++++++---------------------
mm/page_alloc.c | 7 ++++++-
2 files changed, 23 insertions(+), 22 deletions(-)
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 8ba6cb8..23ce67f 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -479,6 +479,21 @@ bool process_shares_mm(struct task_struct *p, struct mm_struct *mm)
static struct task_struct *oom_reaper_list;
static DEFINE_SPINLOCK(oom_reaper_lock);
+/*
+ * We have to make sure not to cause premature new oom victim selection.
+ *
+ * __alloc_pages_may_oom() oom_reap_task_mm()/exit_mmap()
+ * mutex_trylock(&oom_lock)
+ * get_page_from_freelist(ALLOC_WMARK_HIGH) # fails
+ * unmap_page_range() # frees some memory
+ * set_bit(MMF_OOM_SKIP)
+ * out_of_memory()
+ * select_bad_process()
+ * test_bit(MMF_OOM_SKIP) # selects new oom victim
+ * mutex_unlock(&oom_lock)
+ *
+ * Therefore, the callers hold oom_lock when calling this function.
+ */
void __oom_reap_task_mm(struct mm_struct *mm)
{
struct vm_area_struct *vma;
@@ -523,20 +538,6 @@ static bool oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
{
bool ret = true;
- /*
- * We have to make sure to not race with the victim exit path
- * and cause premature new oom victim selection:
- * oom_reap_task_mm exit_mm
- * mmget_not_zero
- * mmput
- * atomic_dec_and_test
- * exit_oom_victim
- * [...]
- * out_of_memory
- * select_bad_process
- * # no TIF_MEMDIE task selects new victim
- * unmap_page_range # frees some memory
- */
mutex_lock(&oom_lock);
if (!down_read_trylock(&mm->mmap_sem)) {
@@ -1077,15 +1078,9 @@ bool out_of_memory(struct oom_control *oc)
dump_header(oc, NULL);
panic("Out of memory and no killable processes...\n");
}
- if (oc->chosen && oc->chosen != (void *)-1UL) {
+ if (oc->chosen && oc->chosen != (void *)-1UL)
oom_kill_process(oc, !is_memcg_oom(oc) ? "Out of memory" :
"Memory cgroup out of memory");
- /*
- * Give the killed process a good chance to exit before trying
- * to allocate memory again.
- */
- schedule_timeout_killable(1);
- }
return !!oc->chosen;
}
@@ -1111,4 +1106,5 @@ void pagefault_out_of_memory(void)
return;
out_of_memory(&oc);
mutex_unlock(&oom_lock);
+ schedule_timeout_killable(1);
}
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 22320ea27..e90f152 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3471,7 +3471,6 @@ void warn_alloc(gfp_t gfp_mask, nodemask_t *nodemask, const char *fmt, ...)
*/
if (!mutex_trylock(&oom_lock)) {
*did_some_progress = 1;
- schedule_timeout_uninterruptible(1);
return NULL;
}
@@ -4238,6 +4237,12 @@ bool gfp_pfmemalloc_allowed(gfp_t gfp_mask)
/* Retry as long as the OOM killer is making progress */
if (did_some_progress) {
no_progress_loops = 0;
+ /*
+ * This schedule_timeout_*() serves as a guaranteed sleep for
+ * PF_WQ_WORKER threads when __zone_watermark_ok() == false.
+ */
+ if (!tsk_is_oom_victim(current))
+ schedule_timeout_uninterruptible(1);
goto retry;
}
--
1.8.3.1
