On Mon 01-06-15 21:34:27, Tetsuo Handa wrote:
> Michal Hocko wrote:
> > On Mon 01-06-15 21:10:18, Tetsuo Handa wrote:
> > > Michal Hocko wrote:
> > > > On Mon 01-06-15 19:51:05, Tetsuo Handa wrote:
> > > > [...]
> > > > > How can all fatal_signal_pending() "struct task_struct" get access to memory
> > > > > reserves when only one of fatal_signal_pending() "struct task_struct" has
> > > > > TIF_MEMDIE ?
> > > >
> > > > Because of
> > > > /*
> > > > * If current has a pending SIGKILL or is exiting, then automatically
> > > > * select it. The goal is to allow it to allocate so that it may
> > > > * quickly exit and free its memory.
> > > > *
> > > > * But don't select if current has already released its mm and cleared
> > > > * TIF_MEMDIE flag at exit_mm(), otherwise an OOM livelock may occur.
> > > > */
> > > > if (current->mm &&
> > > > (fatal_signal_pending(current) || task_will_free_mem(current))) {
> > > > mark_oom_victim(current);
> > > > goto out;
> > > > }
> > >
> > > Then, what guarantees that the thread which is between
> > > down_write(¤t->mm->mmap_sem) and up_write(¤t->mm->mmap_sem)
> > > (or whatever locks which are blocking the OOM victim) calls out_of_memory() ?
> > > That thread might be doing !__GFP_FS allocation request.
> >
> > Could you point to such a place?
>
> I think sequence shown below is possible.
>
> [Thread1-in-Porcess1 Thread2-in-Porcess1] [Thread3-in-Process2]
>
> mutex_lock(&inode->i_mutex);
> kmalloc(GFP_KERNEL)
> Invokes the OOM killer
> Receives TIF_MEMDIE
> Receives SIGKILL
> Receives SIGKILL
> mutex_lock(&inode->i_mutex); <= Waiting forever
> kmalloc(GFP_NOFS); <= Can't return because out_of_memory() is not called.
> mutex_unlock(&inode->i_mutex);
> kmalloc(GFP_NOFS);
> mutex_unlock(&inode->i_mutex);
But this doesn't have anything to do with mm sharing, does it? I mean
this needs a fix anyway and giving access to memory reserves to threads
or processes sharing the mm doesn't fix the problem. This needs a more
generic solution.
--
Michal Hocko
SUSE Labs
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