linux-kernel - Re: [PATCH RFC v2 01/20] mm/slab: add rcu_barrier() to kvfree_rcu_barrier_on

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Message-ID: <3d05c227-5a3b-44c7-8b1b-e7ac4a003b55@suse.cz>
Date: Wed, 14 Jan 2026 14:02:43 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Harry Yoo <harry.yoo@...cle.com>
Cc: Petr Tesarik <ptesarik@...e.com>, Christoph Lameter <cl@...two.org>,
 David Rientjes <rientjes@...gle.com>,
 Roman Gushchin <roman.gushchin@...ux.dev>, Hao Li <hao.li@...ux.dev>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Uladzislau Rezki <urezki@...il.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 Suren Baghdasaryan <surenb@...gle.com>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 Alexei Starovoitov <ast@...nel.org>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev,
 bpf@...r.kernel.org, kasan-dev@...glegroups.com,
 kernel test robot <oliver.sang@...el.com>, stable@...r.kernel.org
Subject: Re: [PATCH RFC v2 01/20] mm/slab: add rcu_barrier() to
 kvfree_rcu_barrier_on_cache()

On 1/14/26 12:14, Harry Yoo wrote:
> For the record, an accurate analysis of the problem (as discussed
> off-list):
> 
> It turns out the object freed by sheaf_flush_unused() was in KASAN
> percpu quarantine list (confirmed by dumping the list) by the time
> __kmem_cache_shutdown() returns an error.
> 
> Quarantined objects are supposed to be flushed by kasan_cache_shutdown(),
> but things go wrong if the rcu callback (rcu_free_sheaf_nobarn()) is
> processed after kasan_cache_shutdown() finishes.
> 
> That's why rcu_barrier() in __kmem_cache_shutdown() didn't help,
> because it's called after kasan_cache_shutdown().
> 
> Calling rcu_barrier() in kvfree_rcu_barrier_on_cache() guarantees
> that it'll be added to the quarantine list before kasan_cache_shutdown()
> is called. So it's a valid fix!

Thanks a lot! Will incorporate to commit log.
This being KASAN-only means further reducing the urgency.