Hi Oleg, I was waiting for this one!
On Mon, 2 Dec 2013 16:24:23 +0100 Oleg Nesterov <o...@redhat.com> wrote: > Hello. > > This was reported several times, I believe the first report is > http://marc.info/?l=linux-kernel&m=127688978121665. Hmm, 3 years > ago. The lockless while_each_thread() is racy and broken, almost > every user can loop forever. > > Recently people started to report they actually hit this problem in > oom_kill.c. This doesn't really matter and I can be wrong, but in > fact I do not think they really hit this race, it is very unlikely. The race is very easy to catch if you have a process with several threads, all of which allocates memory simultaneously. This leads to: 1) OOMk selects and sends SIGKILL to one of the threads 2) another thread invokes OOMk and the first thread gets selected, but it gets unhashed before while_each_thread... > Another problem with while_each_thread() is that it is very easy > to use it wrongly, and oom_kill.c is the good example. > > I came to conclusion that it is practically impossible to send a > single series which fixes all problems, too many different users. > > So 1/2 adds the new for_each_thread() interface, and 2/2 fixes oom > kill as an example. > > We obviously need a lot more changes like 2/2 before we can kill > while_each_thread() and task_struct->thread_group, but I hope they > will be straighforward. And in fact I hope that task->thread_group > can go away before we change all users of while_each_thread(). > > David, et al, I din't actually test 2/2, I do not know how. Please > review, although it looks simple. The patches look correct and my test case no longer hangs, so Reviewed-and-Tested-by: Sergey Dyasly <dse...@gmail.com> > > Oleg. > > include/linux/init_task.h | 2 ++ > include/linux/sched.h | 12 ++++++++++++ > kernel/exit.c | 1 + > kernel/fork.c | 7 +++++++ > mm/oom_kill.c | 37 ++++++++++++++++++++----------------- > 5 files changed, 42 insertions(+), 17 deletions(-) > -- Sergey Dyasly <dse...@gmail.com> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
