Cc William and azur who might have encountered this problem.
On Thu, Nov 28, 2013 at 05:09:16AM +0000, Ma, Xindong wrote:
> From: Leon Ma <xindong.ma@xxxxxxxxx>
> Date: Thu, 28 Nov 2013 12:46:09 +0800
> Subject: [PATCH] Fix race between oom kill and task exit
>
> There is a race between oom kill and task exit. Scenario is:
> TASK A TASK B
> TASK B is selected to oom kill
> in oom_kill_process()
> check PF_EXITING of TASK B
> task call do_exit()
> task set PF_EXITING flag
> write_lock_irq(&tasklist_lock);
> remove TASK B from thread group in __unhash_process()
> write_unlock_irq(&tasklist_lock);
> read_lock(&tasklist_lock);
> traverse threads of TASK B
> read_unlock(&tasklist_lock);
>
> After that, the following traversal of threads in TASK B will not end because TASK B is not in the thread group:
> do {
> ....
> } while_each_thread(p, t);
>
> Signed-off-by: Leon Ma <xindong.ma@xxxxxxxxx>
> Signed-off-by: xiaobing tu <xiaobing.tu@xxxxxxxxx>
> ---
> mm/oom_kill.c | 20 ++++++++++----------
> 1 files changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 1e4a600..32ec88d 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -412,16 +412,6 @@ void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
> static DEFINE_RATELIMIT_STATE(oom_rs, DEFAULT_RATELIMIT_INTERVAL,
> DEFAULT_RATELIMIT_BURST);
>
> - /*
> - * 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) {
> - set_tsk_thread_flag(p, TIF_MEMDIE);
> - put_task_struct(p);
> - return;
> - }
> -
> if (__ratelimit(&oom_rs))
> dump_header(p, gfp_mask, order, memcg, nodemask);
>
> @@ -437,6 +427,16 @@ void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
> * still freeing memory.
> */
> read_lock(&tasklist_lock);
> + /*
> + * 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) {
> + set_tsk_thread_flag(p, TIF_MEMDIE);
> + put_task_struct(p);
> + read_unlock(&tasklist_lock);
> + return;
> + }
> do {
> list_for_each_entry(child, &t->children, sibling) {
> unsigned int child_points;
> --
> 1.7.4.1
>
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