On Sun 03-07-16 11:40:41, Tetsuo Handa wrote:
> >From 00b7a14653c9700429f89e4512f6000a39cce59d Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Date: Sat, 2 Jul 2016 23:03:03 +0900
> Subject: [PATCH 6/8] mm,oom_reaper: Stop clearing TIF_MEMDIE on remote thread.
>
> Since oom_has_pending_mm() controls whether to select next OOM victim,
> we no longer need to clear TIF_MEMDIE on remote thread. Therefore,
> revert related changes in commit 36324a990cf578b5 ("oom: clear TIF_MEMDIE
> after oom_reaper managed to unmap the address space") and
> commit e26796066fdf929c ("oom: make oom_reaper freezable") and
> commit 74070542099c66d8 ("oom, suspend: fix oom_reaper vs.
> oom_killer_disable race").
The last revert is not safe. See
http://lkml.kernel.org/r/1467365190-24640-3-git-send-email-mhocko@xxxxxxxxxx
> This patch temporarily breaks what commit 36324a990cf578b5 ("oom: clear
> TIF_MEMDIE after oom_reaper managed to unmap the address space") and
> commit 449d777d7ad6d7f9 ("mm, oom_reaper: clear TIF_MEMDIE for all tasks
> queued for oom_reaper") try to solve due to oom_has_pending_mm().
> Future patch in this series will fix it.
>
> Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> ---
> include/linux/oom.h | 2 +-
> kernel/exit.c | 2 +-
> kernel/power/process.c | 12 ------------
> mm/oom_kill.c | 15 ++-------------
> 4 files changed, 4 insertions(+), 27 deletions(-)
>
> diff --git a/include/linux/oom.h b/include/linux/oom.h
> index 5991d41..4844325 100644
> --- a/include/linux/oom.h
> +++ b/include/linux/oom.h
> @@ -98,7 +98,7 @@ extern enum oom_scan_t oom_scan_process_thread(struct oom_control *oc,
>
> extern bool out_of_memory(struct oom_control *oc);
>
> -extern void exit_oom_victim(struct task_struct *tsk);
> +extern void exit_oom_victim(void);
>
> extern int register_oom_notifier(struct notifier_block *nb);
> extern int unregister_oom_notifier(struct notifier_block *nb);
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 84ae830..1b1dada 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -511,7 +511,7 @@ static void exit_mm(struct task_struct *tsk)
> mm_update_next_owner(mm);
> mmput(mm);
> if (test_thread_flag(TIF_MEMDIE))
> - exit_oom_victim(tsk);
> + exit_oom_victim();
> }
>
> static struct task_struct *find_alive_thread(struct task_struct *p)
> diff --git a/kernel/power/process.c b/kernel/power/process.c
> index 0c2ee97..df058be 100644
> --- a/kernel/power/process.c
> +++ b/kernel/power/process.c
> @@ -146,18 +146,6 @@ int freeze_processes(void)
> if (!error && !oom_killer_disable())
> error = -EBUSY;
>
> - /*
> - * There is a hard to fix race between oom_reaper kernel thread
> - * and oom_killer_disable. oom_reaper calls exit_oom_victim
> - * before the victim reaches exit_mm so try to freeze all the tasks
> - * again and catch such a left over task.
> - */
> - if (!error) {
> - pr_info("Double checking all user space processes after OOM killer disable... ");
> - error = try_to_freeze_tasks(true);
> - pr_cont("\n");
> - }
> -
> if (error)
> thaw_processes();
> return error;
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 55e0ffb..45e7de2 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -582,15 +582,7 @@ static void oom_reap_task(struct task_struct *tsk)
> debug_show_all_locks();
>
> done:
> - /*
> - * Clear TIF_MEMDIE because the task shouldn't be sitting on a
> - * reasonably reclaimable memory anymore or it is not a good candidate
> - * for the oom victim right now because it cannot release its memory
> - * itself nor by the oom reaper.
> - */
> tsk->oom_reaper_list = NULL;
> - exit_oom_victim(tsk);
> -
> /* Drop a reference taken by wake_oom_reaper */
> put_task_struct(tsk);
> /* Drop a reference taken above. */
> @@ -600,8 +592,6 @@ done:
>
> static int oom_reaper(void *unused)
> {
> - set_freezable();
> -
> while (true) {
> struct task_struct *tsk = NULL;
>
> @@ -688,10 +678,9 @@ void mark_oom_victim(struct task_struct *tsk, struct oom_control *oc)
> /**
> * exit_oom_victim - note the exit of an OOM victim
> */
> -void exit_oom_victim(struct task_struct *tsk)
> +void exit_oom_victim(void)
> {
> - if (!test_and_clear_tsk_thread_flag(tsk, TIF_MEMDIE))
> - return;
> + clear_thread_flag(TIF_MEMDIE);
>
> if (!atomic_dec_return(&oom_victims))
> wake_up_all(&oom_victims_wait);
> --
> 1.8.3.1
--
Michal Hocko
SUSE Labs
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