Messages in this thread | | | Date | Thu, 16 Nov 2023 08:14:47 -0800 | From | Roman Gushchin <> | Subject | Re: [PATCH] mm: kmem: properly initialize local objcg variable in current_obj_cgroup() |
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On Thu, Nov 16, 2023 at 08:04:18AM +0100, Vlastimil Babka wrote: > On 11/16/23 03:51, Roman Gushchin wrote: > > Actually the problem is caused by uninitialized local variable in > > current_obj_cgroup(). If the root memory cgroup is set as an active > > memory cgroup for a charging scope (as in the trace, where systemd > > tries to create the first non-root cgroup, so the parent cgroup is > > the root cgroup), the "for" loop is skipped and uninitialized objcg is > > returned, causing a panic down the accounting stack. > > > > The fix is trivial: initialize the objcg variable to NULL > > unconditionally before the "for" loop. > > > > Fixes: e86828e5446d ("mm: kmem: scoped objcg protection") > > Reported-by: Erhard Furtner <erhard_f@mailbox.org> > > Closes: https://github.com/ClangBuiltLinux/linux/issues/1959 > > Signed-off-by: Roman Gushchin (Cruise) <roman.gushchin@linux.dev> > > Cc: Shakeel Butt <shakeelb@google.com> > > Cc: Vlastimil Babka <vbabka@suse.cz> > > Cc: David Rientjes <rientjes@google.com> > > Cc: Dennis Zhou <dennis@kernel.org> > > Cc: Johannes Weiner <hannes@cmpxchg.org> > > Cc: Michal Hocko <mhocko@kernel.org> > > Cc: Muchun Song <muchun.song@linux.dev> > > Cc: stable@vger.kernel.org > > Acked-by: Vlastimil Babka <vbabka@suse.cz>
Thanks! > > We could also do this to make it less confusing? > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 774bd6e21e27..a08bcec661b6 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -3175,7 +3175,6 @@ __always_inline struct obj_cgroup *current_obj_cgroup(void) > objcg = rcu_dereference_check(memcg->objcg, 1); > if (likely(objcg)) > break; > - objcg = NULL; > } > > return objcg;
Yeah, good catch, it's a remaining of the code with try_get() inside the loop.
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Thank you!
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