linux-kernel - Re: [PATCH RT] mm/memcg: Fix recursive locking on refill_stock() on PREEMPT

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Message-ID: <20230817091224.nqKGjRlK@linutronix.de>
Date:   Thu, 17 Aug 2023 11:12:24 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     zachary.goldstein@...current-rt.com,
        "Luis Claudio R. Goncalves" <lgoncalv@...hat.com>,
        stable-rt@...r.kernel.org
Cc:     linux-mm@...ck.org, cgroups@...r.kernel.org,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org
Subject: Re: [PATCH RT] mm/memcg: Fix recursive locking on refill_stock() on
 PREEMPT_RT

On 2023-08-10 15:05:34 [-0400], Zachary Goldstein via B4 Relay wrote:
> From: Zachary Goldstein <zachary.goldstein@...current-rt.com>
> 
> 5.10 suffers from the same recursive locking issue that
> commit a848d25434de4 ("mm/memcg: Opencode the inner part of
> obj_cgroup_uncharge_pages() in drain_obj_stock()") fixes.

This is the commit id from the stable-rt tree for the v5.15 series.
The original commit was af9a3b69e84be ("mm/memcg: opencode the inner
part of obj_cgroup_uncharge_pages() in drain_obj_stock()").

> Modified description from the commit to reflect this patch changes:
> 
> Provide the inner part of refill_stock() as __refill_stock() without
> disabling interrupts. This eases the integration of local_lock_t where
> recursive locking must be avoided.
> Open code __memcg_kmem_uncharge() in drain_obj_stock() and
> obj_cgroup_release() and use __refill_stock(). The caller of
> drain_obj_stock() and obj_cgroup_release() already disables interrupts.
> 
> Signed-off-by: Zachary Goldstein <zachary.goldstein@...current-rt.com>

I would prefer a proper backport similar to the commit you mentioned.
This would include keeping the author ship and so on.
The change itself looks okay.

Sebastian