On 06/02, KOSAKI Motohiro wrote:
>
> Today, I've thought to make some bandaid patches for this issue. but
> yes, I've reached the same conclusion.
>
> If we think multithread and core dump situation, all fixes are just
> bandaid. We can't remove deadlock chance completely.
>
> The deadlock is certenaly worst result, then, minor PF_EXITING optimization
> doesn't have so much worth.
Agreed! I was always wondering if it really helps in practice.
> Subject: [PATCH] oom: remove PF_EXITING check completely
>
> PF_EXITING is wrong check if the task have multiple threads. This patch
> removes it.
>
> Suggested-by: Oleg Nesterov <oleg@xxxxxxxxxx>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> Cc: Nick Piggin <npiggin@xxxxxxx>
> ---
> mm/oom_kill.c | 27 ---------------------------
> 1 files changed, 0 insertions(+), 27 deletions(-)
>
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 9e7f0f9..b06f8d1 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -302,24 +302,6 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
> if (test_tsk_thread_flag(p, TIF_MEMDIE))
> return ERR_PTR(-1UL);
>
> - /*
> - * This is in the process of releasing memory so wait for it
> - * to finish before killing some other task by mistake.
> - *
> - * However, if p is the current task, we allow the 'kill' to
> - * go ahead if it is exiting: this will simply set TIF_MEMDIE,
> - * which will allow it to gain access to memory reserves in
> - * the process of exiting and releasing its resources.
> - * Otherwise we could get an easy OOM deadlock.
> - */
> - if ((p->flags & PF_EXITING) && p->mm) {
> - if (p != current)
> - return ERR_PTR(-1UL);
> -
> - chosen = p;
> - *ppoints = ULONG_MAX;
> - }
> -
> points = badness(p, uptime.tv_sec);
> if (points > *ppoints || !chosen) {
> chosen = p;
> @@ -436,15 +418,6 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
> if (printk_ratelimit())
> dump_header(p, gfp_mask, order, mem);
>
> - /*
> - * 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) {
> - __oom_kill_process(p, mem, 0);
> - return 0;
> - }
> -
> printk(KERN_ERR "%s: kill process %d (%s) score %li or a child\n",
> message, task_pid_nr(p), p->comm, points);
>
> --
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