On Tue, 5 Dec 2017, David Rientjes wrote:
> One way to solve the issue is to have two mm flags: one to indicate the mm
> is entering unmap_vmas(): set the flag, do down_write(&mm->mmap_sem);
> up_write(&mm->mmap_sem), then unmap_vmas(). The oom reaper needs this
> flag clear, not MMF_OOM_SKIP, while holding down_read(&mm->mmap_sem) to be
> allowed to call unmap_page_range(). The oom killer will still defer
> selecting this victim for MMF_OOM_SKIP after unmap_vmas() returns.
>
> The result of that change would be that we do not oom reap from any mm
> entering unmap_vmas(): we let unmap_vmas() do the work itself and avoid
> racing with it.
>
I think we need something like the following?
diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h
--- a/include/linux/sched/coredump.h
+++ b/include/linux/sched/coredump.h
@@ -70,6 +70,7 @@ static inline int get_dumpable(struct mm_struct *mm)
#define MMF_UNSTABLE 22 /* mm is unstable for copy_from_user */
#define MMF_HUGE_ZERO_PAGE 23 /* mm has ever used the global huge zero page */
#define MMF_DISABLE_THP 24 /* disable THP for all VMAs */
+#define MMF_REAPING 25 /* mm is undergoing reaping */
#define MMF_DISABLE_THP_MASK (1 << MMF_DISABLE_THP)
#define MMF_INIT_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK |\
diff --git a/mm/mmap.c b/mm/mmap.c
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3014,16 +3014,11 @@ void exit_mmap(struct mm_struct *mm)
lru_add_drain();
flush_cache_mm(mm);
- tlb_gather_mmu(&tlb, mm, 0, -1);
- /* update_hiwater_rss(mm) here? but nobody should be looking */
- /* Use -1 here to ensure all VMAs in the mm are unmapped */
- unmap_vmas(&tlb, vma, 0, -1);
-
- set_bit(MMF_OOM_SKIP, &mm->flags);
+ set_bit(MMF_REAPING, &mm->flags);
if (unlikely(tsk_is_oom_victim(current))) {
/*
* Wait for oom_reap_task() to stop working on this
- * mm. Because MMF_OOM_SKIP is already set before
+ * mm. Because MMF_REAPING is already set before
* calling down_read(), oom_reap_task() will not run
* on this "mm" post up_write().
*
@@ -3036,6 +3031,11 @@ void exit_mmap(struct mm_struct *mm)
down_write(&mm->mmap_sem);
up_write(&mm->mmap_sem);
}
+ tlb_gather_mmu(&tlb, mm, 0, -1);
+ /* update_hiwater_rss(mm) here? but nobody should be looking */
+ /* Use -1 here to ensure all VMAs in the mm are unmapped */
+ unmap_vmas(&tlb, vma, 0, -1);
+ set_bit(MMF_OOM_SKIP, &mm->flags);
free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, USER_PGTABLES_CEILING);
tlb_finish_mmu(&tlb, 0, -1);
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -529,12 +529,12 @@ static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
}
/*
- * MMF_OOM_SKIP is set by exit_mmap when the OOM reaper can't
- * work on the mm anymore. The check for MMF_OOM_SKIP must run
+ * MMF_REAPING is set by exit_mmap when the OOM reaper can't
+ * work on the mm anymore. The check for MMF_REAPING must run
* under mmap_sem for reading because it serializes against the
* down_write();up_write() cycle in exit_mmap().
*/
- if (test_bit(MMF_OOM_SKIP, &mm->flags)) {
+ if (test_bit(MMF_REAPING, &mm->flags)) {
up_read(&mm->mmap_sem);
trace_skip_task_reaping(tsk->pid);
goto unlock_oom;
--
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