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From: Hao Li To: Vlastimil Babka Cc: Harry Yoo , Eric Dumazet , Christoph Lameter , David Rientjes , Roman Gushchin , linux-mm@kvack.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev Subject: Re: [PATCH] slab: replace cache_from_obj() with inline checks Message-ID: References: <20260120-b4-remove_cache_from_obj-v1-1-ace30c41eecf@suse.cz> <8bd3c3e8-9865-4467-86d5-17d891f6f21b@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8bd3c3e8-9865-4467-86d5-17d891f6f21b@suse.cz> X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 736594000A X-Stat-Signature: cgrg8x3t76niextj4ds7ur4yepysx5qy X-Rspam-User: X-HE-Tag: 1768917443-536534 X-HE-Meta: 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 pw9++SIX JMfYklz9yMGky+Ajnfx+D8aYkvcL5a/FBkMTTLlx2LpB2QbIZVwWcu7ERakHRrTZI8FLTaVdcjHElbJXmE4rhIr4goM+S/Xyx42f/vpwvfDnpsnU/LFM3ABh+d2WXuQGs3+c5VqlFHTYo9wgViSSoi+8BNroREE8oQET2fdXKUZWIBEE0n48obQ6ZD/AeyurLjKAYEXUET4MJFEzclCy+0AoQ3s/IH7Di9e29FxGoKVmFVkY6Bg3k5o9YaD6DumudSMAc X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Jan 20, 2026 at 01:55:09PM +0100, Vlastimil Babka wrote: > On 1/20/26 12:57, Hao Li wrote: > > >> @@ -6774,11 +6770,21 @@ static inline struct kmem_cache *cache_from_obj(struct kmem_cache *s, void *x) > >> */ > >> void kmem_cache_free(struct kmem_cache *s, void *x) > >> { > >> - s = cache_from_obj(s, x); > >> - if (!s) > >> - return; > >> + struct slab *slab; > >> + > >> + slab = virt_to_slab(x); > >> + > >> + if (IS_ENABLED(CONFIG_SLAB_FREELIST_HARDENED) || > >> + kmem_cache_debug_flags(s, SLAB_CONSISTENCY_CHECKS)) { > >> + > >> + if (unlikely(!slab || (slab->slab_cache != s))) { > >> + warn_free_bad_obj(s, x); > > > > Just to make sure I'm understanding correctly, are we intentionally not > > releasing the object x in this case? Thanks. > > Yes, it means something went wrong so it's better not to do anything. Got it, that makes sense - thanks! > That was true before this patch as well. I'm still not entirely sure I follow. I read the original code, and it seems like it retrieved the real cache from the object and released the object into that correct cache. Did I misunderstand something? -- Thanks, Hao > > >> + return; > >> + } > >> + } > >> + > >> trace_kmem_cache_free(_RET_IP_, x, s); > >> - slab_free(s, virt_to_slab(x), x, _RET_IP_); > >> + slab_free(s, slab, x, _RET_IP_); > >> } > >> EXPORT_SYMBOL(kmem_cache_free); > >> > >> @@ -7305,7 +7311,7 @@ int build_detached_freelist(struct kmem_cache *s, size_t size, > >> df->s = slab->slab_cache; > >> } else { > >> df->slab = slab; > >> - df->s = cache_from_obj(s, object); /* Support for memcg */ > >> + df->s = s; > >> } > >> > >> /* Start new detached freelist */ > >> > >> --- > >> base-commit: 0f61b1860cc3f52aef9036d7235ed1f017632193 > >> change-id: 20260120-b4-remove_cache_from_obj-190fcaf16789 > >> > >> Best regards, > >> -- > >> Vlastimil Babka > >> >