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b=hPlOkLY3drAbSzxoixpsfbX+/90+C91WbIUKsdvpmRCXqChJck060CdGxWd53JAeW avl16jlf/Wk/+SsZ7OhCN8avfGuLTo9TQUOaYto2vnncJ2tnZALkRDJpQ4kPj+gTtd J5s5k4c+xEKgrPu2YuJArn3qynMR6As8UarLIlJTRmEWOZZEDL8M+RGMHFROs36HfZ yIYQ+ZCMh0FA6+WB2y5oraOHffhPZRzxlV5p8zyTaDTDJQh88z4LzNQLXW0V3Xs+nK 3zyePagoIJwbjnW5t05EvYGDGjIpjxOtJwAFnI98HrFTq2Vup69VE7CP+XSEFyULOw QXgoSKDbP0UzQ== Message-ID: From: sashiko-bot@kernel.org Subject: Re: [PATCH] mm/slab: Call call_rcu() directly from __kfree_rcu_sheaf() in any context Reply-To: sashiko-reviews@lists.linux.dev To: "Puranjay Mohan" , linux-mm@kvack.org Cc: "Vlastimil Babka" , "Harry Yoo" , "Andrew Morton" In-Reply-To: <20261016155340.3304319-1-puranjay@kernel.org> References: <20261016155340.3304319-1-puranjay@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Sat, 17 Oct 2026 15:54:09 +0000 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 56F2A100003 X-Stat-Signature: zriza7rirdf95ggggh8rnzz9r7jz37ap X-Rspam-User: X-HE-Tag: 1792252451-137797 X-HE-Meta: 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 bSmcucFV 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Thank you for your contribution! Sashiko AI review found 2 potential issue(= s) to consider: - [High] mm: call_rcu() list corruption due to reentrancy from NMI - [Low] mm: unused llnode field in struct slab_sheaf -- commit 81da114bf5411864e59d873df170399156acac6d Author: Puranjay Mohan mm/slab: Call call_rcu() directly from __kfree_rcu_sheaf() in any context This patch removes the deferred irq_work fallback for rcu_sheaves and instead calls call_rcu() directly from __kfree_rcu_sheaf() in all contexts. The commit message states that call_rcu() now natively handles reentrancy from NMIs. > diff --git a/mm/slub.c b/mm/slub.c > index 8fbc6bf8ebc51..6c44f4495db5a 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -4145,7 +4145,6 @@ static void flush_all(struct kmem_cache *s) > struct deferred_percpu_work { > struct llist_head objects; > struct llist_head objects_by_rcu; > - struct llist_head rcu_sheaves; > struct irq_work work; > }; [Severity: Low] This isn't a bug, but since this patch removes the rcu_sheaves list and all its associated logic, should the llnode field in struct slab_sheaf also be removed? It appears the llnode field in struct slab_sheaf was only used to defer this call_rcu() invocation. [ ... ] > @@ -6308,22 +6306,8 @@ bool __kfree_rcu_sheaf(struct kmem_cache *s, void = *obj, unsigned int free_flags) > * we flush before local_unlock to make sure a racing > * flush_all_rcu_sheaves() doesn't miss this sheaf > */ > - if (rcu_sheaf) { > - /* > - * With !allow_spin, we might have interrupted call_rcu()'s > - * IRQ-disabled critical section. If IRQs are not disabled, > - * we know that's not the case. > - */ > - if (unlikely(!allow_spin && irqs_disabled())) { > - struct deferred_percpu_work *dpw; > - > - dpw =3D this_cpu_ptr(&deferred_percpu_work); > - if (llist_add(&rcu_sheaf->llnode, &dpw->rcu_sheaves)) > - irq_work_queue(&dpw->work); > - } else { > - call_rcu(&rcu_sheaf->rcu_head, rcu_free_sheaf); > - } > - } > + if (rcu_sheaf) > + call_rcu(&rcu_sheaf->rcu_head, rcu_free_sheaf); [Severity: High] The commit message states: "When it is called with IRQs disabled (from NMI, or re-entered from instrumentation), it stages the callback on a per-CPU list and re-issues it from irq_work." Looking at the implementation of call_rcu() and __call_rcu_common() in kernel/rcu/tree.c, it disables IRQs and synchronously manipulates the callback list. It does not appear to contain an NMI/irq_work fallback. If __kfree_rcu_sheaf() is called from an NMI or tracing context (such as from bpf or perf) while the CPU is already executing call_rcu() or rcu_do_batch(), could this direct call to call_rcu() re-enter the list manipulation and corrupt the RCU callback lists? --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20261016155340.3304= 319-1-puranjay@kernel.org?part=3D1