On Tue, 10 Apr 2018 12:49:02 +0200
Michal Hocko <mho...@kernel.org> wrote:
> But you do realize that what you are proposing is by no means any safer,
> don't you? The memory allocated for the ring buffer is _not_ accounted
> to any process and as such it is not considered by the oom killer when
> picking up an oom victim so you are quite likely to pick up an innocent
> process to be killed. So basically you are risking an allocation runaway
> completely hidden from the OOM killer. Now, the downside of the patch is
> that the OOM_SCORE_ADJ_MIN task might get killed which is something that
> shouldn't happen because it is a contract. I would call this an
> unsolvable problem and a inherent broken design of the oom disabled
> task. So far I haven't heard a single _argument_ why supporting such a
> weird cornercase is desirable when your application can trivial do
>
> fork(); set_oom_score_adj(); exec("echo $VAR > $RINGBUFFER_FILE")
We could do this as a compromise:
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index c9cb9767d49b..40c2e0a56c51 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1185,6 +1185,12 @@ static int __rb_allocate_pages(long nr_pages, struct
list_head *pages, int cpu)
*/
mflags = GFP_KERNEL | __GFP_RETRY_MAYFAIL;
+ /* If we can't OOM this task, then only allocate without reclaim */
+ if (unlikely(current->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)) {
+ mflags = GFP_KERNEL | __GFP_NORETRY;
+ user_thread = false; /* do not set oom_origin */
+ }
+
/*
* If a user thread allocates too much, and si_mem_available()
* reports there's enough memory, even though there is not.
This way, if one sets OOM_SCORE_ADJ_MIN, then we wont set oom_origin
for the task, but we also wont try hard to allocate memory if there is
nothing immediately available.
-- Steve
