On 09/20, Linus Torvalds wrote: > > On Sun, Sep 20, 2015 at 5:56 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote: > > > > In this case the workqueue thread will block. > > What workqueue thread? I must have missed something. I can't understand your and Michal's concerns. > pagefault_out_of_memory -> > out_of_memory -> > oom_kill_process > > as far as I can tell, this can be called by any task. Now, that > pagefault case should only happen when the page fault comes from user > space, but we also have > > __alloc_pages_slowpath -> > __alloc_pages_may_oom -> > out_of_memory -> > oom_kill_process > > which can be called from just about any context (but atomic > allocations will never get here, so it can schedule etc). So yes, in general oom_kill_process() can't call oom_unmap_func() directly. That is why the patch uses queue_work(oom_unmap_func). The workqueue thread takes mmap_sem and frees the memory allocated by user space. If this can lead to deadlock somehow, then we can hit the same deadlock when an oom-killed thread calls exit_mm(). > So what's your point? This can help if the killed process refuse to die and (of course) it doesn't hold the mmap_sem for writing. Say, it waits for some mutex held by the task which tries to alloc the memory and triggers oom. > Explain again just how do you guarantee that you > can take the mmap_sem. This is not guaranteed, down_read(mmap_sem) can block forever. But this means that the (killed) victim never drops mmap_sem / never exits, so we lose anyway. We have no memory, oom-killer is blocked, etc. Oleg. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>