Hello, On (12/08/16 20:00), Tetsuo Handa wrote: [..] > Theread-1 was trying to flush printk log buffer by printk() from > oom_kill_process() with oom_lock held. Thread-2 was appending to printk > log buffer by printk() from warn_alloc() because Thread-2 cannot hold > oom_lock held by Thread-1. As a result, this formed an AB-BA livelock. > > Although warn_alloc() calls printk() aggressively enough to livelock is > problematic, at least we can say that it is wasteful to spend CPU time for > pointless "direct reclaim and warn_alloc()" calls when waiting for the OOM > killer to send SIGKILL. Therefore, this patch replaces mutex_trylock() > with mutex_lock_killable(). > > Replacing mutex_trylock() with mutex_lock_killable() should be safe, for > if somebody by error called __alloc_pages_may_oom() with oom_lock held, > it will livelock because did_some_progress will be set to 1 despite > mutex_trylock() failure. so I have some patches in my own/personal/secret tree. the patches were not yet published to the kernel-list (well, not all of them. I'll do it a bit later). we are moving towards the "printk() just appends the messages to the logbuf" idea: https://gitlab.com/senozhatsky/linux-next-ss/commits/printk-safe-deferred -ss > Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> > --- > mm/page_alloc.c | 12 ++++++++---- > 1 file changed, 8 insertions(+), 4 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 6de9440..6c43d8e 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3037,12 +3037,16 @@ void warn_alloc(gfp_t gfp_mask, const char *fmt, ...) > *did_some_progress = 0; > > /* > - * Acquire the oom lock. If that fails, somebody else is > - * making progress for us. > + * Give the OOM killer enough CPU time for sending SIGKILL. > + * Do not return without a short sleep unless TIF_MEMDIE is set, for > + * currently tsk_is_oom_victim(current) == true does not make > + * gfp_pfmemalloc_allowed() == true via TIF_MEMDIE until > + * mark_oom_victim(current) is called. > */ > - if (!mutex_trylock(&oom_lock)) { > + if (mutex_lock_killable(&oom_lock)) { > *did_some_progress = 1; > - schedule_timeout_uninterruptible(1); > + if (!test_thread_flag(TIF_MEMDIE)) > + schedule_timeout_uninterruptible(1); > return NULL; > } -- 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>