From: "Vlastimil Babka (SUSE)" <vbabka@kernel.org>
To: Shakeel Butt <shakeel.butt@linux.dev>,
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>,
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: Tue, 14 Apr 2026 09:56:36 +0200 [thread overview]
Message-ID: <ef2d8f65-b3b4-4a9c-a77f-78ad1cadff28@kernel.org> (raw)
In-Reply-To: <ad0clnEYxf1H4_S1@linux.dev>
On 4/13/26 18:44, Shakeel Butt wrote:
> 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?
This is obviously a product of LLM producing a patch from the syzbot report.
I suggest we ignore everything from this author.
prev parent reply other threads:[~2026-04-14 7:56 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-13 6:48 Cao Ruichuang
2026-04-13 16:44 ` Shakeel Butt
2026-04-14 7:56 ` Vlastimil Babka (SUSE) [this message]
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