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    SubjectRe: [PATCH] Fix race between oom kill and task exit
    Date
    From
    > Od: Johannes Weiner <hannes@cmpxchg.org>
    > Komu: "Ma, Xindong" <xindong.ma@intel.com>
    > Dátum: 28.11.2013 07:54
    > Predmet: Re: [PATCH] Fix race between oom kill and task exit
    >
    > CC: "akpm@linux-foundation.org" <akpm@linux-foundation.org>, "mhocko@suse.cz" <mhocko@suse.cz>, "rientjes@google.com" <rientjes@google.com>, "rusty@rustcorp.com.au" <rusty@rustcorp.com.au>, "linux-mm@kvack.org" <linux-mm@kvack.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "'Peter Zijlstra'" <peterz@infradead.org>, "'gregkh@linuxfoundation.org'" <gregkh@linuxfoundation.org>, "Tu, Xiaobing" <xiaobing.tu@intel.com>, "William Dauchy" <wdauchy@gmail.com>
    >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@intel.com>
    >> 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@intel.com>
    >> Signed-off-by: xiaobing tu <xiaobing.tu@intel.com>
    >> ---
    >> 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
    >>
    >




    Hi Johannes,

    thank you very much! Fortunately, i didn't notice anything like this yet.

    azur
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