On Tue 20-03-18 20:57:55, Tetsuo Handa wrote:
> I found that it is not difficult to hit "oom_reaper: unable to reap pid:"
> messages if the victim thread is doing copy_process(). Since I noticed
> that it is likely helpful to show trace of unable to reap victim thread
> for finding locations which should use killable wait, this patch does so.
>
> [ 226.608508] oom_reaper: unable to reap pid:9261 (a.out)
> [ 226.611971] a.out D13056 9261 6927 0x00100084
> [ 226.615879] Call Trace:
> [ 226.617926] ? __schedule+0x25f/0x780
> [ 226.620559] schedule+0x2d/0x80
> [ 226.623356] rwsem_down_write_failed+0x2bb/0x440
> [ 226.626426] ? rwsem_down_write_failed+0x55/0x440
> [ 226.629458] ? anon_vma_fork+0x124/0x150
> [ 226.632679] call_rwsem_down_write_failed+0x13/0x20
> [ 226.635884] down_write+0x49/0x60
> [ 226.638867] ? copy_process.part.41+0x12f2/0x1fe0
> [ 226.642042] copy_process.part.41+0x12f2/0x1fe0 /* i_mmap_lock_write() in dup_mmap() */
> [ 226.645087] ? _do_fork+0xe6/0x560
> [ 226.647991] _do_fork+0xe6/0x560
> [ 226.650495] ? syscall_trace_enter+0x1a9/0x240
> [ 226.653443] ? retint_user+0x18/0x18
> [ 226.656601] ? page_fault+0x2f/0x50
> [ 226.659159] ? trace_hardirqs_on_caller+0x11f/0x1b0
> [ 226.662399] do_syscall_64+0x74/0x230
> [ 226.664989] entry_SYSCALL_64_after_hwframe+0x42/0xb7
A single stack trace in the changelog would be sufficient IMHO.
Appart from that. What do you expect users will do about this trace?
Sure they will see a path which holds mmap_sem, we will see a bug report
but we can hardly do anything about that. We simply cannot drop the lock
from that path in 99% of situations. So _why_ do we want to add more
information to the log?
[...]
> Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> ---
> mm/oom_kill.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 5336985..900300c 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -41,6 +41,7 @@
> #include <linux/kthread.h>
> #include <linux/init.h>
> #include <linux/mmu_notifier.h>
> +#include <linux/sched/debug.h>
>
> #include <asm/tlb.h>
> #include "internal.h"
> @@ -596,6 +597,7 @@ 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:
> --
> 1.8.3.1
>
--
Michal Hocko
SUSE Labs
