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h=Date:From:To:Cc:Subject:In-Reply-To:References; b=RNNV+cYZ5+aJda8P1sCv52PVqhOWoeLyirlvjLUKSUBqZOYAefQ/InbP9RhJaxp2+ iONedHR86FeYZsi0Ko0TyghBWfBrb5ZrVxVqnTL+/nF5ZvYgF0X3MqeYE03sZsDKb3 6Zzb6TLk5b2bSbnTKSPP+yG4YLX/t2vlFNWeNifc= Date: Thu, 20 Aug 2026 18:20:38 -0700 From: Andrew Morton To: Ye Liu Cc: syzbot , brendan.jackman@linux.dev, hannes@cmpxchg.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mhocko@suse.com, surenb@google.com, syzkaller-bugs@googlegroups.com, vbabka@kernel.org, ziy@nvidia.com, Zhen Ni , Oscar Salvador , Andrey Ryabinin , Alexander Potapenko , Andrey Konovalov , Dmitry Vyukov Subject: Re: [syzbot] [mm?] INFO: rcu detected stall in kvm_vm_release (4) Message-Id: <20260820182038.c45e454506c8cd3c1f21930b@linux-foundation.org> In-Reply-To: References: <6a86fe29.f7a79266.2f965f.004a.GAE@google.com> <20260820092904.7a2b43fff85ed0c13b9c74ab@linux-foundation.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: EFA6C80009 X-Rspam-User: X-Stat-Signature: nirghwsqasbkspdy6u6mrxwp18mg3k8c X-Rspamd-Server: rspam06 X-HE-Tag: 1787275240-413968 X-HE-Meta: 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 lTIUtdv3 N1ZDOjtCdMAySQrNJ6LSMtT+jH5aUfu/DZpnzjaFu4X0NUKDXfd7Oq0Wpem7op3+dpx/O9TF/DqV5pNhqMAeDNYou3pZdhinctU+FOLSEzxjpCK1sGNJmRyuTG8Q4FGilXegppqwkJzgpCnIdTWXl0uWJuOfLcHkCFyl8Q7ujg5JedzfXegE7Sohh0iiN0d4zBW/19pNplOjkihv8ma0nzPPA16t7a50w1I98FJWtJQAz3chwKqaIOys0GP2y+T5TitxSKDgisqw/AcJ4OYFHtiaDekd5ilpxNapGtxpGMLr3teXm32r1AME60MWLf5IwCPw/2TYAwhN16JPz0qWgwT55DB5nzcD+7SSOJrbhybbybLgDYj3406glVbCbslagMCA79518PLf5us5XXpgoPtahNShzMiZzxD5Fg1zA+8f3dSsPBHsPbd8kqxNG0DGTfqSeoLBX5+6jIJeWsWCoMPKcwPUuooxU08Il Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 21 Aug 2026 09:06:48 +0800 Ye Liu wrote: > > : The combination of debug tools: KASAN quarantine processing + ORC > > : unwinder + page_owner stack tracing executed so slowly on the CPU that > > : it exceeded the RCU stall threshold. > > > > (I think we've recently seen the same thing, different callers) > > > > I can't say I'm terribly motivated. page_owner is expensive and if you > > run heavy stress testing with page_owner enabled then such things > > aren't surprising. > > > > Let me Cc a few page_owner and KASAN people, see if they feel > > differently. > > Adding cond_resched() to the qlist_free_all() loop would fix this . > kasan_quarantine_remove_cache() already dose the same in its scanning loop. I don't think cond_resched() does what we want for RCU stalls. And cond_resched() is a no-op without CONFIG_PREEMPT_NONE, which wasn't set here.