On 03/12, David Rientjes wrote:
>
> The oom killer naturally defers killing anything if it finds an eligible
> task that is already exiting and has yet to detach its ->mm. This avoids
> unnecessarily killing tasks when one is already in the exit path and may
> free enough memory that the oom killer is no longer needed. This is
> detected by PF_EXITING since threads that have already detached its ->mm
> are no longer considered at all.
So, this is on top of oom-prevent-unnecessary-oom-kills-or-kernel-panics.patch
I still can't understand which problems that patch tries to solve. Could
you explain why this patch helps in details?
Speaking of "already exiting and has yet to detach its ->mm", did you look
at "[PATCH 2/3] oom: select_bad_process: improve the PF_EXITING check" ?
> The problem with always deferring when a thread is PF_EXITING, however,
> is that it may never actually exit when being traced, specifically if
> another task is tracing it with PTRACE_O_TRACEEXIT. The oom killer does
> not want to defer in this case since there is no guarantee that thread
> will ever exit without intervention.
IOW, you are trying to fight with the test-case I sent,
> + } else {
> + /*
> + * If this task is not being ptraced on exit,
> + * then wait for it to finish before killing
> + * some other task unnecessarily.
> + */
> + if (!(task_ptrace(p->group_leader) &
> + PT_TRACE_EXIT))
> + return ERR_PTR(-1UL);
No, this can't help afaics. It is trivial to change the exploit and
get the same result.
Perhaps I missed something, I didn't read this patch carefully. Will
try to do later.
However. could you please answer my question above?
Also. We have the serious and easily exploitable bugs, I think we
should fix them first. I'll report more details later today.
Oleg.
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