> From: David Rientjes <rientjes@xxxxxxxxxx>
>
> It's possible to livelock the page allocator if a thread has
> mm->mmap_sem and fails to make forward progress because the
> oom killer selects another thread sharing the same ->mm to
> kill that cannot exit until the semaphore is dropped.
>
> The oom killer will not kill multiple tasks at the same time; each oom
> killed task must exit before another task may be killed. Thus, if one
> thread is holding mm->mmap_sem and cannot allocate memory, all threads
> sharing the same ->mm are blocked from exiting as well. In the oom kill
> case, that means the thread holding mm->mmap_sem will never free
> additional memory since it cannot get access to memory reserves and the
> thread that depends on it with access to memory reserves cannot exit
> because it cannot acquire the semaphore. Thus, the page allocators
> livelocks.
>
> When the oom killer is called and current happens to have a pending
> SIGKILL, this patch automatically gives it access to memory reserves and
> returns. Upon returning to the page allocator, its allocation will
> hopefully succeed so it can quickly exit and free its memory. If not,
> the page allocator will fail the allocation if it is not __GFP_NOFAIL.
>
> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> ---
> mm/oom_kill.c | 10 ++++++++++
> 1 files changed, 10 insertions(+), 0 deletions(-)
>
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 67b5fa5..ad85e1b 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -638,6 +638,16 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
> }
>
> /*
> + * If current has a pending SIGKILL, then automatically select it. The
> + * goal is to allow it to allocate so that it may quickly exit and free
> + * its memory.
> + */
> + if (fatal_signal_pending(current)) {
> + set_tsk_thread_flag(current, TIF_MEMDIE);
> + return;
> + }
Self NAK this.
We have no gurantee that current is oom killable. Oh, here is
out_of_memory(), sigh.
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