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b=F6dv9eQBS3DHoFKwspKTOCxDhh2PQeBeZFPAVKhlhtwy8OktZf6MQUUnEbC2Cv/UF 24vR9wkvQDqKQpNZqrT2lzrUkHWRjCipIVudLSxtXHpZ0JESeyVqpCfVYo60JMs3lb Cf7aAdbx4uI2M8tj/XRul15/yMFO+uqoiz6/p0jZbKVpXi91pcdiyQX18AWU7jzeW3 JZ3hVRdB8PZCkJMTfG8YHfMMYiMATCrkqr4MekNd7C0asp+cDRBHSpJS6vvciIUup2 dAuxhiLgwoBqeIGoUfjqGqR6LWyaiU7ub8hVOsWRoPrDtw0ZFZM224IET5Lux/F+qk nv7G8gSm/n5Qw== Date: Tue, 3 Nov 2026 14:58:25 +0000 From: Harry Yoo To: "Vlastimil Babka (SUSE)" Cc: Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Alexei Starovoitov , Pedro Falcato , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [PATCH RFC 2/4] mm/slab: handle allow_spin in slab_free_hook() instead of open coding Message-ID: References: <20260624-kmalloc-nolock-fixes-v1-0-fdf4d17351dd@kernel.org> <20260624-kmalloc-nolock-fixes-v1-2-fdf4d17351dd@kernel.org> <91776136-ecaf-4687-be63-a2c074435462@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <91776136-ecaf-4687-be63-a2c074435462@kernel.org> X-Stat-Signature: idofdffi4fwaqr1rsiicsw59bhk55zsg X-Rspam-User: X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 973D01C0005 X-HE-Tag: 1793717908-35617 X-HE-Meta: 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 97mvvpux r349cPClAM+zKERxNtq3NFHHMz4XFvpD+Vk7zlRhBqm/2ew9hwdIxNPSx2idTPFg1p+LAEk2eV9noj5Vlp6XLtQvXgRAge1OHa2F161f36sBV88GU+S3de5iiXutjmCpK2x3551MEmFCIJ/iRlriJrFdCTiXG42ip6uYoE7t/oWjdiao0WkykUHkpXSW2VzWEF8/ASQclX0K4PQJATgGCD2P5lsxYJHn5CwJFqsFUQXtbwkCA1jwjDm/6OgCnrCZ+jI5YEEewmkKr8CONwJK8ahUbc2ImxgRPm42pn1GF0RzsS7w= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 Apologies for the late reply... On Fri, Jun 26, 2026 at 04:41:22PM +0200, Vlastimil Babka (SUSE) wrote: > On 6/24/26 15:11, Harry Yoo (Oracle) wrote: > > diff --git a/mm/slub.c b/mm/slub.c > > index 32672a92581b..85760c8ff2e2 100644 > > --- a/mm/slub.c > > +++ b/mm/slub.c > > @@ -2611,41 +2611,52 @@ struct rcu_delayed_free { > > * - memcg_slab_post_alloc_hook() > > * - alloc_tagging_slab_alloc_hook() > > * > > + * slab_free_hook() assumes that memcg_slab_free_hook() and > > + * alloc_tagging_slab_free_hook() are already invoked. > > + * > > * Free hooks that must handle missing corresponding alloc hooks: > > * - kmemleak_free_recursive() > > * - kfence_free() > > * > > - * Free hooks that have no alloc hook counterpart, and thus safe to call: > > + * Free hooks that have no alloc hook counterpart, and thus safe to call > > + * when spinning is allowed: > > * - debug_check_no_locks_freed() > > * - debug_check_no_obj_freed() > > * - __kcsan_check_access() > > */ > > static __always_inline > > bool slab_free_hook(struct kmem_cache *s, void *x, bool init, > > - bool after_rcu_delay) > > + bool after_rcu_delay, bool allow_spin) > > { > > /* Are the object contents still accessible? */ > > bool still_accessible = (s->flags & SLAB_TYPESAFE_BY_RCU) && !after_rcu_delay; > > > > - kmemleak_free_recursive(x, s->flags); > > kmsan_slab_free(s, x); > > > > - debug_check_no_locks_freed(x, s->object_size); > > - > > - if (!(s->flags & SLAB_DEBUG_OBJECTS)) > > - debug_check_no_obj_freed(x, s->object_size); > > - > > - /* Use KCSAN to help debug racy use-after-free. */ > > - if (!still_accessible) > > - __kcsan_check_access(x, s->object_size, > > - KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ASSERT); > > - > > - if (kfence_free(x)) > > - return false; > > + if (likely(allow_spin)) { > > + /* These hooks acquire spinlocks */ > > + kmemleak_free_recursive(x, s->flags); > > + debug_check_no_locks_freed(x, s->object_size); > > This line shouldn't be here? You mean because debug_check_no_locks_freed() doesn't acquire a lock when there is no bug to report? That's fair, but I didn't want to introduce functional changes in this patch as kfree_nolock() hasn't been calling it anyway. So separated this (and KCSAN checks) to patch 3 in v2 as they only acquire locks when reporting a bug. (Taking risk of deadlock for bug reporting just like KASAN). > > + if (!(s->flags & SLAB_DEBUG_OBJECTS)) > > + debug_check_no_obj_freed(x, s->object_size); > > + /* Use KCSAN to help debug racy use-after-free. */ > > + if (!still_accessible) > > + __kcsan_check_access(x, s->object_size, > > + KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ASSERT); > > + if (kfence_free(x)) > > + return false; > > The whole block now misses free space lines that it had. Adjusted in v2, thanks! -- Cheers, Harry / Hyeonggon