From: Shakeel Butt <shakeel.butt@linux.dev>
To: Cao Ruichuang <create0818@163.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@kernel.org>,
Roman Gushchin <roman.gushchin@linux.dev>,
Muchun Song <muchun.song@linux.dev>,
Andrew Morton <akpm@linux-foundation.org>,
David Hildenbrand <david@kernel.org>,
Lorenzo Stoakes <ljs@kernel.org>,
"Liam R. Howlett" <Liam.Howlett@oracle.com>,
Vlastimil Babka <vbabka@kernel.org>,
Mike Rapoport <rppt@kernel.org>,
Suren Baghdasaryan <surenb@google.com>,
cgroups@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org,
syzbot+1a3353a77896e73a8f53@syzkaller.appspotmail.com
Subject: Re: [PATCH] mm/memcontrol: restore irq wrapper for lruvec_stat_mod_folio()
Date: Mon, 13 Apr 2026 09:44:08 -0700 [thread overview]
Message-ID: <ad0clnEYxf1H4_S1@linux.dev> (raw)
In-Reply-To: <20260413064833.964-1-create0818@163.com>
On Mon, Apr 13, 2026 at 02:48:33PM +0800, Cao Ruichuang wrote:
> Commit c1bd09994c4d ("memcg: remove __lruvec_stat_mod_folio") removed
> the local_irq_save/restore wrapper around lruvec_stat_mod_folio(), based
> on the assumption that the underlying stat update path was already
> IRQ-safe.
Why is that an assumption? Please explain how lruvec_stat_mod_folio() is not
safe against IRQs?
>
> That assumption is too broad for lruvec_stat_mod_folio() callers.
> This helper is not just a thin stat primitive. It also resolves
> folio -> memcg -> lruvec under a helper-managed RCU read-side section.
>
> syzbot now reports a PREEMPT_RT warning from:
The syzbot link you have provided has the kernel config without PREEMPT_RT?
Where does this claim come from?
>
> __filemap_add_folio()
> -> lruvec_stat_mod_folio()
> -> __rcu_read_unlock()
>
> ending in bad unlock balance / negative RCU nesting.
If there is bad unlock balance, how is disabling/enabling IRQs would solve that
issue?
next prev parent reply other threads:[~2026-04-13 16:44 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-13 6:48 [PATCH] mm/memcontrol: restore irq wrapper for lruvec_stat_mod_folio() Cao Ruichuang
2026-04-13 16:44 ` Shakeel Butt [this message]
2026-04-14 7:56 ` Vlastimil Babka (SUSE)
2026-04-15 16:22 ` create0818
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