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    SubjectRe: [PATCH] oom killer: break from infinite loop
    On Thu, 25 Mar 2010 00:25:05 +0800
    Anfei Zhou <anfei.zhou@gmail.com> wrote:

    > In multi-threading environment, if the current task(A) have got
    > the mm->mmap_sem semaphore, and the thread(B) in the same process
    > is selected to be oom killed, because they shares the same semaphore,
    > thread B can not really be killed. So __alloc_pages_slowpath turns
    > to be a infinite loop. Here set all the threads in the group to
    > TIF_MEMDIE, it gets a chance to break and exit.
    >
    > Signed-off-by: Anfei Zhou <anfei.zhou@gmail.com>
    > ---
    > mm/oom_kill.c | 4 ++++
    > 1 files changed, 4 insertions(+), 0 deletions(-)
    >
    > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
    > index 9b223af..aab9892 100644
    > --- a/mm/oom_kill.c
    > +++ b/mm/oom_kill.c
    > @@ -381,6 +381,8 @@ static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
    > */
    > static void __oom_kill_task(struct task_struct *p, int verbose)
    > {
    > + struct task_struct *t;
    > +
    > if (is_global_init(p)) {
    > WARN_ON(1);
    > printk(KERN_WARNING "tried to kill init!\n");
    > @@ -412,6 +414,8 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
    > */
    > p->rt.time_slice = HZ;
    > set_tsk_thread_flag(p, TIF_MEMDIE);
    > + for (t = next_thread(p); t != p; t = next_thread(t))
    > + set_tsk_thread_flag(t, TIF_MEMDIE);
    >
    > force_sig(SIGKILL, p);

    Don't we need some sort of locking while walking that ring?
    Unintuitively it appears to be spin_lock_irq(&p->sighand->siglock).




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