| Message ID | alpine.DEB.2.21.2001141519280.200484@chino.kir.corp.google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm, oom: dump stack of victim when reaping failed | expand |
On Tue 14-01-20 15:20:04, David Rientjes wrote: > When a process cannot be oom reaped, for whatever reason, currently the > list of locks that are held is currently dumped to the kernel log. > > Much more interesting is the stack trace of the victim that cannot be > reaped. If the stack trace is dumped, we have the ability to find > related occurrences in the same kernel code and hopefully solve the > issue that is making it wedged. > > Dump the stack trace when a process fails to be oom reaped. Yes, this is really helpful. > Signed-off-by: David Rientjes <rientjes@google.com> Acked-by: Michal Hocko <mhocko@suse.com> Thanks! > --- > mm/oom_kill.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -26,6 +26,7 @@ > #include <linux/sched/mm.h> > #include <linux/sched/coredump.h> > #include <linux/sched/task.h> > +#include <linux/sched/debug.h> > #include <linux/swap.h> > #include <linux/timex.h> > #include <linux/jiffies.h> > @@ -620,6 +621,7 @@ static void oom_reap_task(struct task_struct *tsk) > > pr_info("oom_reaper: unable to reap pid:%d (%s)\n", > task_pid_nr(tsk), tsk->comm); > + sched_show_task(tsk); > debug_show_all_locks(); > > done:
On Wed, 15 Jan 2020, Tetsuo Handa wrote: > >> When a process cannot be oom reaped, for whatever reason, currently the > >> list of locks that are held is currently dumped to the kernel log. > >> > >> Much more interesting is the stack trace of the victim that cannot be > >> reaped. If the stack trace is dumped, we have the ability to find > >> related occurrences in the same kernel code and hopefully solve the > >> issue that is making it wedged. > >> > >> Dump the stack trace when a process fails to be oom reaped. > > > > Yes, this is really helpful. > > tsk would be a thread group leader, but the thread which got stuck is not > always a thread group leader. Maybe dump all threads in that thread group > without PF_EXITING (or something) ? > That's possible, yes. I think it comes down to the classic problem of how much info in the kernel log on oom kill is too much. Stacks for all threads that match the mm being reaped may be *very* verbose. I'm currently tracking a stall in oom reaping where the victim doesn't always have a lock held so we don't know where it's at in the kernel; I'm hoping that a stack for the thread group leader will at least shed some light on it.
On Thu, 16 Jan 2020, Tetsuo Handa wrote: > > I'm > > currently tracking a stall in oom reaping where the victim doesn't always > > have a lock held so we don't know where it's at in the kernel; I'm hoping > > that a stack for the thread group leader will at least shed some light on > > it. > > > > This change was already proposed at > https://lore.kernel.org/linux-mm/20180320122818.GL23100@dhcp22.suse.cz/ . > Hmm, seems the patch didn't get followed up on but I obviously agree with it :) > And according to that proposal, it is likely i_mmap_lock_write() in dup_mmap() > in copy_process(). We tried to make that lock killable but we gave it up > because nobody knows whether it is safe to do make it killable. > I haven't encountered that particular problem yet; one problem that I've found is a victim holding cgroup_threadgroup_rwsem in the exit path, another problem is the victim not holding any locks at all which is more concerning (why isn't it making forward progress?). This patch intends to provide a clue for the latter. Aside: we may also want to consider the possibility of doing immediate additional oom killing if the initial victim is too small. We rely on the oom reaper to solve livelocks like this by freeing memory so that allocators can drop locks that the victim depends on. If the victim is too small (we have victims <1MB because of oom_score_adj +1000!) we may want to consider additional immediate oom killing because it simply won't free enough memory.
diff --git a/mm/oom_kill.c b/mm/oom_kill.c --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -26,6 +26,7 @@ #include <linux/sched/mm.h> #include <linux/sched/coredump.h> #include <linux/sched/task.h> +#include <linux/sched/debug.h> #include <linux/swap.h> #include <linux/timex.h> #include <linux/jiffies.h> @@ -620,6 +621,7 @@ static void oom_reap_task(struct task_struct *tsk) pr_info("oom_reaper: unable to reap pid:%d (%s)\n", task_pid_nr(tsk), tsk->comm); + sched_show_task(tsk); debug_show_all_locks(); done:
When a process cannot be oom reaped, for whatever reason, currently the list of locks that are held is currently dumped to the kernel log. Much more interesting is the stack trace of the victim that cannot be reaped. If the stack trace is dumped, we have the ability to find related occurrences in the same kernel code and hopefully solve the issue that is making it wedged. Dump the stack trace when a process fails to be oom reaped. Signed-off-by: David Rientjes <rientjes@google.com> --- mm/oom_kill.c | 2 ++ 1 file changed, 2 insertions(+)