On Fri, 8 Jan 2016, Tetsuo Handa wrote:
> The OOM reaper kernel thread can reclaim OOM victim's memory before the
> victim terminates. But since oom_kill_process() tries to kill children of
> the memory hog process first, the OOM reaper can not reclaim enough memory
> for terminating the victim if the victim is consuming little memory. The
> result is OOM livelock as usual, for timeout based next OOM victim
> selection is not implemented.
>
> While SysRq-f (manual invocation of the OOM killer) can wake up the OOM
> killer, the OOM killer chooses the same OOM victim which already has
> TIF_MEMDIE. This is effectively disabling SysRq-f.
>
> This patch excludes TIF_MEMDIE processes from candidates so that the
> memory hog process itself will be killed when all children of the memory
> hog process got stuck with TIF_MEMDIE pending.
>
> [ 120.078776] oom-write invoked oom-killer: order=0, oom_score_adj=0, gfp_mask=0x24280ca(GFP_HIGHUSER_MOVABLE|GFP_ZERO)
> [ 120.088610] oom-write cpuset=/ mems_allowed=0
> [ 120.095558] CPU: 0 PID: 9546 Comm: oom-write Not tainted 4.4.0-rc6-next-20151223 #260
> (...snipped...)
> [ 120.194148] [ pid ] uid tgid total_vm rss nr_ptes nr_pmds swapents oom_score_adj name
> (...snipped...)
> [ 120.260191] [ 9546] 1000 9546 541716 453473 896 6 0 0 oom-write
> [ 120.262166] [ 9547] 1000 9547 40 1 3 2 0 0 write
> [ 120.264071] [ 9548] 1000 9548 40 1 3 2 0 0 write
> [ 120.265939] [ 9549] 1000 9549 40 1 4 2 0 0 write
> [ 120.267794] [ 9550] 1000 9550 40 1 3 2 0 0 write
> [ 120.269654] [ 9551] 1000 9551 40 1 3 2 0 0 write
> [ 120.271447] [ 9552] 1000 9552 40 1 3 2 0 0 write
> [ 120.273220] [ 9553] 1000 9553 40 1 3 2 0 0 write
> [ 120.274975] [ 9554] 1000 9554 40 1 3 2 0 0 write
> [ 120.276745] [ 9555] 1000 9555 40 1 3 2 0 0 write
> [ 120.278516] [ 9556] 1000 9556 40 1 3 2 0 0 write
> [ 120.280227] Out of memory: Kill process 9546 (oom-write) score 892 or sacrifice child
> [ 120.282010] Killed process 9549 (write) total-vm:160kB, anon-rss:4kB, file-rss:0kB, shmem-rss:0kB
> (...snipped...)
> [ 122.506001] systemd-journal invoked oom-killer: order=0, oom_score_adj=0, gfp_mask=0x24201ca(GFP_HIGHUSER_MOVABLE|GFP_COLD)
> [ 122.515041] systemd-journal cpuset=/ mems_allowed=0
> (...snipped...)
> [ 122.697515] [ 9546] 1000 9546 541716 458687 906 6 0 0 oom-write
> [ 122.699492] [ 9551] 1000 9551 40 1 3 2 0 0 write
> [ 122.701399] [ 9552] 1000 9552 40 1 3 2 0 0 write
> [ 122.703282] [ 9553] 1000 9553 40 1 3 2 0 0 write
> [ 122.705188] [ 9554] 1000 9554 40 1 3 2 0 0 write
> [ 122.707017] [ 9555] 1000 9555 40 1 3 2 0 0 write
> [ 122.708842] [ 9556] 1000 9556 40 1 3 2 0 0 write
> [ 122.710675] Out of memory: Kill process 9546 (oom-write) score 902 or sacrifice child
> [ 122.712475] Killed process 9551 (write) total-vm:160kB, anon-rss:4kB, file-rss:0kB, shmem-rss:0kB
> [ 139.606508] sysrq: SysRq : Manual OOM execution
> [ 139.612371] kworker/0:2 invoked oom-killer: order=-1, oom_score_adj=0, gfp_mask=0x24000c0(GFP_KERNEL)
> [ 139.620210] kworker/0:2 cpuset=/ mems_allowed=0
> (...snipped...)
> [ 139.795759] [ 9546] 1000 9546 541716 458687 906 6 0 0 oom-write
> [ 139.797649] [ 9551] 1000 9551 40 0 3 2 0 0 write
> [ 139.799526] [ 9552] 1000 9552 40 1 3 2 0 0 write
> [ 139.801368] [ 9553] 1000 9553 40 1 3 2 0 0 write
> [ 139.803249] [ 9554] 1000 9554 40 1 3 2 0 0 write
> [ 139.805020] [ 9555] 1000 9555 40 1 3 2 0 0 write
> [ 139.806799] [ 9556] 1000 9556 40 1 3 2 0 0 write
> [ 139.808524] Out of memory: Kill process 9546 (oom-write) score 902 or sacrifice child
> [ 139.810216] Killed process 9552 (write) total-vm:160kB, anon-rss:4kB, file-rss:0kB, shmem-rss:0kB
> (...snipped...)
> [ 142.571815] [ 9546] 1000 9546 541716 458687 906 6 0 0 oom-write
> [ 142.573840] [ 9551] 1000 9551 40 0 3 2 0 0 write
> [ 142.575754] [ 9552] 1000 9552 40 0 3 2 0 0 write
> [ 142.577633] [ 9553] 1000 9553 40 1 3 2 0 0 write
> [ 142.579433] [ 9554] 1000 9554 40 1 3 2 0 0 write
> [ 142.581250] [ 9555] 1000 9555 40 1 3 2 0 0 write
> [ 142.583003] [ 9556] 1000 9556 40 1 3 2 0 0 write
> [ 142.585055] Out of memory: Kill process 9546 (oom-write) score 902 or sacrifice child
> [ 142.586796] Killed process 9553 (write) total-vm:160kB, anon-rss:4kB, file-rss:0kB, shmem-rss:0kB
> [ 143.599058] sysrq: SysRq : Manual OOM execution
> [ 143.604300] kworker/0:2 invoked oom-killer: order=-1, oom_score_adj=0, gfp_mask=0x24000c0(GFP_KERNEL)
> (...snipped...)
> [ 143.783739] [ 9546] 1000 9546 541716 458687 906 6 0 0 oom-write
> [ 143.785691] [ 9551] 1000 9551 40 0 3 2 0 0 write
> [ 143.787532] [ 9552] 1000 9552 40 0 3 2 0 0 write
> [ 143.789377] [ 9553] 1000 9553 40 0 3 2 0 0 write
> [ 143.791172] [ 9554] 1000 9554 40 1 3 2 0 0 write
> [ 143.792985] [ 9555] 1000 9555 40 1 3 2 0 0 write
> [ 143.794730] [ 9556] 1000 9556 40 1 3 2 0 0 write
> [ 143.796723] Out of memory: Kill process 9546 (oom-write) score 902 or sacrifice child
> [ 143.798338] Killed process 9554 (write) total-vm:160kB, anon-rss:4kB, file-rss:0kB, shmem-rss:0kB
> [ 144.374525] sysrq: SysRq : Manual OOM execution
> [ 144.379779] kworker/0:2 invoked oom-killer: order=-1, oom_score_adj=0, gfp_mask=0x24000c0(GFP_KERNEL)
> (...snipped...)
> [ 144.560718] [ 9546] 1000 9546 541716 458687 906 6 0 0 oom-write
> [ 144.562657] [ 9551] 1000 9551 40 0 3 2 0 0 write
> [ 144.564560] [ 9552] 1000 9552 40 0 3 2 0 0 write
> [ 144.566369] [ 9553] 1000 9553 40 0 3 2 0 0 write
> [ 144.568246] [ 9554] 1000 9554 40 0 3 2 0 0 write
> [ 144.570001] [ 9555] 1000 9555 40 1 3 2 0 0 write
> [ 144.571794] [ 9556] 1000 9556 40 1 3 2 0 0 write
> [ 144.573502] Out of memory: Kill process 9546 (oom-write) score 902 or sacrifice child
> [ 144.575119] Killed process 9555 (write) total-vm:160kB, anon-rss:4kB, file-rss:0kB, shmem-rss:0kB
> [ 145.158485] sysrq: SysRq : Manual OOM execution
> [ 145.163600] kworker/0:2 invoked oom-killer: order=-1, oom_score_adj=0, gfp_mask=0x24000c0(GFP_KERNEL)
> (...snipped...)
> [ 145.346059] [ 9546] 1000 9546 541716 458687 906 6 0 0 oom-write
> [ 145.348012] [ 9551] 1000 9551 40 0 3 2 0 0 write
> [ 145.349954] [ 9552] 1000 9552 40 0 3 2 0 0 write
> [ 145.351817] [ 9553] 1000 9553 40 0 3 2 0 0 write
> [ 145.353701] [ 9554] 1000 9554 40 0 3 2 0 0 write
> [ 145.355568] [ 9555] 1000 9555 40 0 3 2 0 0 write
> [ 145.357319] [ 9556] 1000 9556 40 1 3 2 0 0 write
> [ 145.359114] Out of memory: Kill process 9546 (oom-write) score 902 or sacrifice child
> [ 145.360733] Killed process 9556 (write) total-vm:160kB, anon-rss:4kB, file-rss:0kB, shmem-rss:0kB
> [ 169.158408] sysrq: SysRq : Manual OOM execution
> [ 169.163612] kworker/0:2 invoked oom-killer: order=-1, oom_score_adj=0, gfp_mask=0x24000c0(GFP_KERNEL)
> (...snipped...)
> [ 169.343115] [ 9546] 1000 9546 541716 458687 906 6 0 0 oom-write
> [ 169.345053] [ 9551] 1000 9551 40 0 3 2 0 0 write
> [ 169.346884] [ 9552] 1000 9552 40 0 3 2 0 0 write
> [ 169.348965] [ 9553] 1000 9553 40 0 3 2 0 0 write
> [ 169.350893] [ 9554] 1000 9554 40 0 3 2 0 0 write
> [ 169.352713] [ 9555] 1000 9555 40 0 3 2 0 0 write
> [ 169.354551] [ 9556] 1000 9556 40 0 3 2 0 0 write
> [ 169.356450] Out of memory: Kill process 9546 (oom-write) score 902 or sacrifice child
> [ 169.358105] Killed process 9551 (write) total-vm:160kB, anon-rss:0kB, file-rss:0kB, shmem-rss:0kB
> [ 178.950315] sysrq: SysRq : Manual OOM execution
> [ 178.955560] kworker/0:2 invoked oom-killer: order=-1, oom_score_adj=0, gfp_mask=0x24000c0(GFP_KERNEL)
> (...snipped...)
> [ 179.140752] [ 9546] 1000 9546 541716 458687 906 6 0 0 oom-write
> [ 179.142653] [ 9551] 1000 9551 40 0 3 2 0 0 write
> [ 179.144997] [ 9552] 1000 9552 40 0 3 2 0 0 write
> [ 179.146849] [ 9553] 1000 9553 40 0 3 2 0 0 write
> [ 179.148654] [ 9554] 1000 9554 40 0 3 2 0 0 write
> [ 179.150411] [ 9555] 1000 9555 40 0 3 2 0 0 write
> [ 179.152291] [ 9556] 1000 9556 40 0 3 2 0 0 write
> [ 179.154002] Out of memory: Kill process 9546 (oom-write) score 902 or sacrifice child
> [ 179.155666] Killed process 9551 (write) total-vm:160kB, anon-rss:0kB, file-rss:0kB, shmem-rss:0kB
>
> Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
> mm/oom_kill.c | 30 +++++++++++++++++++++++++++---
> 1 file changed, 27 insertions(+), 3 deletions(-)
>
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index ef89fda..edce443 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -125,6 +125,30 @@ found:
> }
>
> /*
> + * Treat the whole process p as unkillable when one of threads has
> + * TIF_MEMDIE pending. Otherwise, we may end up setting TIF_MEMDIE
> + * on the same victim forever (e.g. making SysRq-f unusable).
> + */
> +static struct task_struct *find_lock_non_victim_task_mm(struct task_struct *p)
> +{
> + struct task_struct *t;
> +
> + rcu_read_lock();
> +
> + for_each_thread(p, t) {
> + if (likely(!test_tsk_thread_flag(t, TIF_MEMDIE)))
> + continue;
> + t = NULL;
> + goto found;
> + }
> + t = find_lock_task_mm(p);
> + found:
> + rcu_read_unlock();
> +
> + return t;
> +}
> +
> +/*
> * order == -1 means the oom kill is required by sysrq, otherwise only
> * for display purposes.
> */
> @@ -171,7 +195,7 @@ unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
> if (oom_unkillable_task(p, memcg, nodemask))
> return 0;
>
> - p = find_lock_task_mm(p);
> + p = find_lock_non_victim_task_mm(p);
> if (!p)
> return 0;
>
I understand how this may make your test case pass, but I simply don't
understand how this could possibly be the correct thing to do. This would
cause oom_badness() to return 0 for any process where a thread has
TIF_MEMDIE set. If the oom killer is called from the page allocator,
kills a thread, and it is recalled before that thread may exit, then this
will panic the system if there are no other eligible processes to kill.
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