| Message ID | e865a044-2c10-9858-f4ef-254bc71d6cc2@i-love.sakura.ne.jp (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v3] oom, oom_reaper: do not enqueue same task twice | expand |
On Sun 27-01-19 23:57:38, Tetsuo Handa wrote: [...] > >From 9c9e935fc038342c48461aabca666f1b544e32b1 Mon Sep 17 00:00:00 2001 > From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> > Date: Sun, 27 Jan 2019 23:51:37 +0900 > Subject: [PATCH v3] oom, oom_reaper: do not enqueue same task twice > > Arkadiusz reported that enabling memcg's group oom killing causes > strange memcg statistics where there is no task in a memcg despite > the number of tasks in that memcg is not 0. It turned out that there > is a bug in wake_oom_reaper() which allows enqueuing same task twice > which makes impossible to decrease the number of tasks in that memcg > due to a refcount leak. > > This bug existed since the OOM reaper became invokable from > task_will_free_mem(current) path in out_of_memory() in Linux 4.7, > but memcg's group oom killing made it easier to trigger this bug by > calling wake_oom_reaper() on the same task from one out_of_memory() > request. > > Fix this bug using an approach used by commit 855b018325737f76 > ("oom, oom_reaper: disable oom_reaper for oom_kill_allocating_task"). > As a side effect of this patch, this patch also avoids enqueuing > multiple threads sharing memory via task_will_free_mem(current) path. > > Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> > Reported-by: Arkadiusz Miśkiewicz <arekm@maven.pl> > Tested-by: Arkadiusz Miśkiewicz <arekm@maven.pl> > Fixes: af8e15cc85a25315 ("oom, oom_reaper: do not enqueue task if it is on the oom_reaper_list head") Acked-by: Michal Hocko <mhocko@suse.com> > --- > include/linux/sched/coredump.h | 1 + > mm/oom_kill.c | 4 ++-- > 2 files changed, 3 insertions(+), 2 deletions(-) > > diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h > index ec912d0..ecdc654 100644 > --- a/include/linux/sched/coredump.h > +++ b/include/linux/sched/coredump.h > @@ -71,6 +71,7 @@ static inline int get_dumpable(struct mm_struct *mm) > #define MMF_HUGE_ZERO_PAGE 23 /* mm has ever used the global huge zero page */ > #define MMF_DISABLE_THP 24 /* disable THP for all VMAs */ > #define MMF_OOM_VICTIM 25 /* mm is the oom victim */ > +#define MMF_OOM_REAP_QUEUED 26 /* mm was queued for oom_reaper */ > #define MMF_DISABLE_THP_MASK (1 << MMF_DISABLE_THP) > > #define MMF_INIT_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK |\ > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > index f0e8cd9..059e617 100644 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -647,8 +647,8 @@ static int oom_reaper(void *unused) > > static void wake_oom_reaper(struct task_struct *tsk) > { > - /* tsk is already queued? */ > - if (tsk == oom_reaper_list || tsk->oom_reaper_list) > + /* mm is already queued? */ > + if (test_and_set_bit(MMF_OOM_REAP_QUEUED, &tsk->signal->oom_mm->flags)) > return; > > get_task_struct(tsk); > -- > 1.8.3.1
On Sun, Jan 27, 2019 at 11:57:38PM +0900, Tetsuo Handa wrote: > On 2019/01/27 20:40, Michal Hocko wrote: > > On Sun 27-01-19 19:56:06, Tetsuo Handa wrote: > >> On 2019/01/27 17:37, Michal Hocko wrote: > >>> Thanks for the analysis and the patch. This should work, I believe but > >>> I am not really thrilled to overload the meaning of the MMF_UNSTABLE. > >>> The flag is meant to signal accessing address space is not stable and it > >>> is not aimed to synchronize oom reaper with the oom path. > >>> > >>> Can we make use mark_oom_victim directly? I didn't get to think that > >>> through right now so I might be missing something but this should > >>> prevent repeating queueing as well. > >> > >> Yes, TIF_MEMDIE would work. But you are planning to remove TIF_MEMDIE. Also, > >> TIF_MEMDIE can't avoid enqueuing many threads sharing mm_struct to the OOM > >> reaper. There is no need to enqueue many threads sharing mm_struct because > >> the OOM reaper acts on mm_struct rather than task_struct. Thus, enqueuing > >> based on per mm_struct flag sounds better, but MMF_OOM_VICTIM cannot be > >> set from wake_oom_reaper(victim) because victim's mm might be already inside > >> exit_mmap() when wake_oom_reaper(victim) is called after task_unlock(victim). > >> > >> We could reintroduce MMF_OOM_KILLED in commit 855b018325737f76 > >> ("oom, oom_reaper: disable oom_reaper for oom_kill_allocating_task") > >> if you don't like overloading the meaning of the MMF_UNSTABLE. But since > >> MMF_UNSTABLE is available in Linux 4.9+ kernels (which covers all LTS stable > >> versions with the OOM reaper support), we can temporarily use MMF_UNSTABLE > >> for ease of backporting. > > > > I agree that a per-mm state is more optimal but I would rather fix the > > issue in a clear way first and only then think about an optimization on > > top. Queueing based on mark_oom_victim (whatever that uses to guarantee > > the victim is marked atomically and only once) makes sense from the > > conceptual point of view and it makes a lot of sense to start from > > there. MMF_UNSTABLE has a completely different purpose. So unless you > > see a correctness issue with that then I would rather go that way. > > > > Then, adding a per mm_struct flag is better. I don't see the difference > between reusing MMF_UNSTABLE as a flag for whether wake_oom_reaper() for > that victim's memory was already called (what you think as an overload) > and reusing TIF_MEMDIE as a flag for whether wake_oom_reaper() for that > victim thread can be called (what I think as an overload). We want to > remove TIF_MEMDIE, and we can actually remove TIF_MEMDIE if you stop > whack-a-mole "can you observe it in real workload/program?" game. > I don't see a correctness issue with TIF_MEMDIE but I don't want to go > TIF_MEMDIE way. > > > > From 9c9e935fc038342c48461aabca666f1b544e32b1 Mon Sep 17 00:00:00 2001 > From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> > Date: Sun, 27 Jan 2019 23:51:37 +0900 > Subject: [PATCH v3] oom, oom_reaper: do not enqueue same task twice > > Arkadiusz reported that enabling memcg's group oom killing causes > strange memcg statistics where there is no task in a memcg despite > the number of tasks in that memcg is not 0. It turned out that there > is a bug in wake_oom_reaper() which allows enqueuing same task twice > which makes impossible to decrease the number of tasks in that memcg > due to a refcount leak. > > This bug existed since the OOM reaper became invokable from > task_will_free_mem(current) path in out_of_memory() in Linux 4.7, > but memcg's group oom killing made it easier to trigger this bug by > calling wake_oom_reaper() on the same task from one out_of_memory() > request. > > Fix this bug using an approach used by commit 855b018325737f76 > ("oom, oom_reaper: disable oom_reaper for oom_kill_allocating_task"). > As a side effect of this patch, this patch also avoids enqueuing > multiple threads sharing memory via task_will_free_mem(current) path. > > Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> > Reported-by: Arkadiusz Miśkiewicz <arekm@maven.pl> > Tested-by: Arkadiusz Miśkiewicz <arekm@maven.pl> > Fixes: af8e15cc85a25315 ("oom, oom_reaper: do not enqueue task if it is on the oom_reaper_list head") Thank you, Tetsuo! Acked-by: Roman Gushchin <guro@fb.com>
On Sun, 27 Jan 2019 23:57:38 +0900 Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp> wrote: > Arkadiusz reported that enabling memcg's group oom killing causes > strange memcg statistics where there is no task in a memcg despite > the number of tasks in that memcg is not 0. It turned out that there > is a bug in wake_oom_reaper() which allows enqueuing same task twice > which makes impossible to decrease the number of tasks in that memcg > due to a refcount leak. > > This bug existed since the OOM reaper became invokable from > task_will_free_mem(current) path in out_of_memory() in Linux 4.7, > but memcg's group oom killing made it easier to trigger this bug by > calling wake_oom_reaper() on the same task from one out_of_memory() > request. > > Fix this bug using an approach used by commit 855b018325737f76 > ("oom, oom_reaper: disable oom_reaper for oom_kill_allocating_task"). > As a side effect of this patch, this patch also avoids enqueuing > multiple threads sharing memory via task_will_free_mem(current) path. > Do we think this is serious enough to warrant a -stable backport?
On Mon 28-01-19 10:15:13, Andrew Morton wrote: > On Sun, 27 Jan 2019 23:57:38 +0900 Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp> wrote: > > > Arkadiusz reported that enabling memcg's group oom killing causes > > strange memcg statistics where there is no task in a memcg despite > > the number of tasks in that memcg is not 0. It turned out that there > > is a bug in wake_oom_reaper() which allows enqueuing same task twice > > which makes impossible to decrease the number of tasks in that memcg > > due to a refcount leak. > > > > This bug existed since the OOM reaper became invokable from > > task_will_free_mem(current) path in out_of_memory() in Linux 4.7, > > but memcg's group oom killing made it easier to trigger this bug by > > calling wake_oom_reaper() on the same task from one out_of_memory() > > request. > > > > Fix this bug using an approach used by commit 855b018325737f76 > > ("oom, oom_reaper: disable oom_reaper for oom_kill_allocating_task"). > > As a side effect of this patch, this patch also avoids enqueuing > > multiple threads sharing memory via task_will_free_mem(current) path. > > > > Do we think this is serious enough to warrant a -stable backport? Yes, I would go with stable backport.
Hi Tetsuo, On Sun, Jan 27, 2019 at 11:57:38PM +0900, Tetsuo Handa wrote: > From 9c9e935fc038342c48461aabca666f1b544e32b1 Mon Sep 17 00:00:00 2001 > From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> > Date: Sun, 27 Jan 2019 23:51:37 +0900 > Subject: [PATCH v3] oom, oom_reaper: do not enqueue same task twice > > Arkadiusz reported that enabling memcg's group oom killing causes > strange memcg statistics where there is no task in a memcg despite > the number of tasks in that memcg is not 0. It turned out that there > is a bug in wake_oom_reaper() which allows enqueuing same task twice > which makes impossible to decrease the number of tasks in that memcg > due to a refcount leak. > > This bug existed since the OOM reaper became invokable from > task_will_free_mem(current) path in out_of_memory() in Linux 4.7, > but memcg's group oom killing made it easier to trigger this bug by > calling wake_oom_reaper() on the same task from one out_of_memory() > request. This changelog seems a little terse compared to how tricky this is. Can you please include an explanation here *how* this bug is possible? I.e. the race condition that causes the function te be entered twice and the existing re-entrance check in there to fail. > Fix this bug using an approach used by commit 855b018325737f76 > ("oom, oom_reaper: disable oom_reaper for oom_kill_allocating_task"). > As a side effect of this patch, this patch also avoids enqueuing > multiple threads sharing memory via task_will_free_mem(current) path.
Johannes Weiner wrote: > On Sun, Jan 27, 2019 at 11:57:38PM +0900, Tetsuo Handa wrote: > > This bug existed since the OOM reaper became invokable from > > task_will_free_mem(current) path in out_of_memory() in Linux 4.7, > > but memcg's group oom killing made it easier to trigger this bug by > > calling wake_oom_reaper() on the same task from one out_of_memory() > > request. > > This changelog seems a little terse compared to how tricky this is. > > Can you please include an explanation here *how* this bug is possible? > I.e. the race condition that causes the function te be entered twice > and the existing re-entrance check in there to fail. OK. Here is an updated patch. Only changelog part has changed. I hope this will provide enough information to stable kernel maintainers. ---------- From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Subject: oom, oom_reaper: do not enqueue same task twice Arkadiusz reported that enabling memcg's group oom killing causes strange memcg statistics where there is no task in a memcg despite the number of tasks in that memcg is not 0. It turned out that there is a bug in wake_oom_reaper() which allows enqueuing same task twice which makes impossible to decrease the number of tasks in that memcg due to a refcount leak. This bug existed since the OOM reaper became invokable from task_will_free_mem(current) path in out_of_memory() in Linux 4.7, T1@P1 |T2@P1 |T3@P1 |OOM reaper ----------+----------+----------+------------ # Processing an OOM victim in a different memcg domain. try_charge() mem_cgroup_out_of_memory() mutex_lock(&oom_lock) try_charge() mem_cgroup_out_of_memory() mutex_lock(&oom_lock) try_charge() mem_cgroup_out_of_memory() mutex_lock(&oom_lock) out_of_memory() oom_kill_process(P1) do_send_sig_info(SIGKILL, @P1) mark_oom_victim(T1@P1) wake_oom_reaper(T1@P1) # T1@P1 is enqueued. mutex_unlock(&oom_lock) out_of_memory() mark_oom_victim(T2@P1) wake_oom_reaper(T2@P1) # T2@P1 is enqueued. mutex_unlock(&oom_lock) out_of_memory() mark_oom_victim(T1@P1) wake_oom_reaper(T1@P1) # T1@P1 is enqueued again due to oom_reaper_list == T2@P1 && T1@P1->oom_reaper_list == NULL. mutex_unlock(&oom_lock) # Completed processing an OOM victim in a different memcg domain. spin_lock(&oom_reaper_lock) # T1P1 is dequeued. spin_unlock(&oom_reaper_lock) but memcg's group oom killing made it easier to trigger this bug by calling wake_oom_reaper() on the same task from one out_of_memory() request. Fix this bug using an approach used by commit 855b018325737f76 ("oom, oom_reaper: disable oom_reaper for oom_kill_allocating_task"). As a side effect of this patch, this patch also avoids enqueuing multiple threads sharing memory via task_will_free_mem(current) path. Fixes: af8e15cc85a25315 ("oom, oom_reaper: do not enqueue task if it is on the oom_reaper_list head") Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Reported-by: Arkadiusz Miśkiewicz <arekm@maven.pl> Tested-by: Arkadiusz Miśkiewicz <arekm@maven.pl> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Roman Gushchin <guro@fb.com> Cc: Tejun Heo <tj@kernel.org> Cc: Aleksa Sarai <asarai@suse.de> Cc: Jay Kamat <jgkamat@fb.com> Cc: Johannes Weiner <hannes@cmpxchg.org> --- include/linux/sched/coredump.h | 1 + mm/oom_kill.c | 4 ++-- 2 files changed, 3 insertions(+), 2 deletions(-) diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h index ec912d0..ecdc654 100644 --- a/include/linux/sched/coredump.h +++ b/include/linux/sched/coredump.h @@ -71,6 +71,7 @@ static inline int get_dumpable(struct mm_struct *mm) #define MMF_HUGE_ZERO_PAGE 23 /* mm has ever used the global huge zero page */ #define MMF_DISABLE_THP 24 /* disable THP for all VMAs */ #define MMF_OOM_VICTIM 25 /* mm is the oom victim */ +#define MMF_OOM_REAP_QUEUED 26 /* mm was queued for oom_reaper */ #define MMF_DISABLE_THP_MASK (1 << MMF_DISABLE_THP) #define MMF_INIT_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK |\ diff --git a/mm/oom_kill.c b/mm/oom_kill.c index f0e8cd9..059e617 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -647,8 +647,8 @@ static int oom_reaper(void *unused) static void wake_oom_reaper(struct task_struct *tsk) { - /* tsk is already queued? */ - if (tsk == oom_reaper_list || tsk->oom_reaper_list) + /* mm is already queued? */ + if (test_and_set_bit(MMF_OOM_REAP_QUEUED, &tsk->signal->oom_mm->flags)) return; get_task_struct(tsk);
diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h index ec912d0..ecdc654 100644 --- a/include/linux/sched/coredump.h +++ b/include/linux/sched/coredump.h @@ -71,6 +71,7 @@ static inline int get_dumpable(struct mm_struct *mm) #define MMF_HUGE_ZERO_PAGE 23 /* mm has ever used the global huge zero page */ #define MMF_DISABLE_THP 24 /* disable THP for all VMAs */ #define MMF_OOM_VICTIM 25 /* mm is the oom victim */ +#define MMF_OOM_REAP_QUEUED 26 /* mm was queued for oom_reaper */ #define MMF_DISABLE_THP_MASK (1 << MMF_DISABLE_THP) #define MMF_INIT_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK |\ diff --git a/mm/oom_kill.c b/mm/oom_kill.c index f0e8cd9..059e617 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -647,8 +647,8 @@ static int oom_reaper(void *unused) static void wake_oom_reaper(struct task_struct *tsk) { - /* tsk is already queued? */ - if (tsk == oom_reaper_list || tsk->oom_reaper_list) + /* mm is already queued? */ + if (test_and_set_bit(MMF_OOM_REAP_QUEUED, &tsk->signal->oom_mm->flags)) return; get_task_struct(tsk);