From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Shakeel Butt <shakeel.butt@linux.dev>,
Andrew Morton <akpm@linux-foundation.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@kernel.org>,
Roman Gushchin <roman.gushchin@linux.dev>,
Muchun Song <muchun.song@linux.dev>,
linux-mm@kvack.org, cgroups@vger.kernel.org,
linux-kernel@vger.kernel.org,
Meta kernel team <kernel-team@meta.com>
Subject: Re: [RFC PATCH 06/10] memcg: do obj_cgroup_put inside drain_obj_stock
Date: Fri, 14 Mar 2025 12:35:33 +0100 [thread overview]
Message-ID: <20250314113533.jNrVXeyr@linutronix.de> (raw)
In-Reply-To: <0b3ab5e5-e684-44ce-b6ed-276ad37784e6@suse.cz>
On 2025-03-14 11:17:28 [+0100], Vlastimil Babka wrote:
> On 3/14/25 07:15, Shakeel Butt wrote:
> > Previously we could not call obj_cgroup_put() inside the local lock
> > because on the put on the last reference, the release function
> > obj_cgroup_release() may try to re-acquire the local lock. However that
> > chain has been broken. Now simply do obj_cgroup_put() inside
> > drain_obj_stock() instead of returning the old objcg.
> >
> > Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
>
> Hm is this really safe? I can see obj_cgroup_release() doing
> percpu_ref_exit() -> kfree(), do we have guaranteed that allocation won't be
> also in a kmemcg and recurse?
This was like this until commit
5675114623872 ("mm/memcg: protect memcg_stock with a local_lock_t")
at which point the put had to happen outside. This "percpu_ref_exit() ->
kfree()" was also prior this commit.
Sebastian
next prev parent reply other threads:[~2025-03-14 11:35 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-03-14 6:15 [RFC PATCH 00/10] memcg: stock code cleanups Shakeel Butt
2025-03-14 6:15 ` [RFC PATCH 01/10] memcg: remove root memcg check from refill_stock Shakeel Butt
2025-03-14 6:15 ` [RFC PATCH 02/10] memcg: decouple drain_obj_stock from local stock Shakeel Butt
2025-03-14 9:57 ` Vlastimil Babka
2025-03-14 6:15 ` [RFC PATCH 03/10] memcg: introduce memcg_uncharge Shakeel Butt
2025-03-14 10:01 ` Vlastimil Babka
2025-03-14 6:15 ` [RFC PATCH 04/10] memcg: manually inline __refill_stock Shakeel Butt
2025-03-14 10:05 ` Vlastimil Babka
2025-03-14 6:15 ` [RFC PATCH 05/10] memcg: no refilling stock from obj_cgroup_release Shakeel Butt
2025-03-14 10:09 ` Vlastimil Babka
2025-03-14 11:26 ` Sebastian Andrzej Siewior
2025-03-14 15:25 ` Shakeel Butt
2025-03-14 6:15 ` [RFC PATCH 06/10] memcg: do obj_cgroup_put inside drain_obj_stock Shakeel Butt
2025-03-14 10:17 ` Vlastimil Babka
2025-03-14 11:35 ` Sebastian Andrzej Siewior [this message]
2025-03-14 15:29 ` Shakeel Butt
2025-03-14 6:15 ` [RFC PATCH 07/10] memcg: use __mod_memcg_state in drain_obj_stock Shakeel Butt
2025-03-14 10:27 ` Vlastimil Babka
2025-03-14 11:44 ` Sebastian Andrzej Siewior
2025-03-14 11:38 ` Sebastian Andrzej Siewior
2025-03-14 6:15 ` [RFC PATCH 08/10] memcg: assert in_task for couple of local_lock holders Shakeel Butt
2025-03-14 6:15 ` [RFC PATCH 09/10] memcg: trylock stock for objcg Shakeel Butt
2025-03-14 11:47 ` Sebastian Andrzej Siewior
2025-03-14 15:33 ` Shakeel Butt
2025-03-14 6:15 ` [RFC PATCH 10/10] memcg: no more irq disabling for stock locks Shakeel Butt
2025-03-14 10:54 ` Vlastimil Babka
2025-03-14 11:58 ` Sebastian Andrzej Siewior
2025-03-14 15:55 ` Shakeel Butt
2025-03-14 16:42 ` Sebastian Andrzej Siewior
2025-03-14 17:02 ` Shakeel Butt
2025-03-14 17:38 ` Shakeel Butt
2025-03-14 18:19 ` Sebastian Andrzej Siewior
2025-03-14 13:33 ` [RFC PATCH 00/10] memcg: stock code cleanups Vlastimil Babka
2025-03-14 16:03 ` Shakeel Butt
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