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Perez de Azpillaga" Subject: Re: [PATCH v2] mm/slab: sample slab_state once in kmem_cache_destroy() Message-ID: References: <20261014150844.8536-1-kaloz@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261014150844.8536-1-kaloz@kernel.org> X-Stat-Signature: r71yhikw5di5m8p6ktgadef1pwy1pffp X-Rspam-User: X-Rspamd-Queue-Id: 219DE160006 X-Rspamd-Server: rspam08 X-HE-Tag: 1792007216-932555 X-HE-Meta: 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 sJC1+agE J4Q1rf5qXztEdli+pZ3SrNO0X6RNCVywXA6YKpQ9lfnHztESiV/hQw5Skng7j4k4QGKRab2tTpN9hw/RFE8gwZLd2TIQd0IzEN2hXB12lIReWHAJ0mM0F6fCNAVzSv7jPmBIGpDE5ovjZdkExmwAp85rqworFFNDD8szY/gEy3xRK2UrvbBnoAH0gp+TqM65nSn+33U2ZgYriuFawuBCjpIDf3+u+ZXU2FEygae45eYfvdSaAfm9Me55Tj+X39n5QJ7SjjLt63qX9zqy/2ynWkfvQb/HgPznClcOX43JHuKgt/s5GCmHD2aARcIA9Ai4FB7COKwqv91Bzzz7wUt8Y5MuAow== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Oct 14, 2026 at 05:08:43PM +0200, Imre Kaloz wrote: > kmem_cache_release() tests slab_state >= FULL after kmem_cache_destroy() > has dropped slab_mutex and unlinked the cache, and for a > SLAB_TYPESAFE_BY_RCU cache after rcu_barrier(). If slab_late_init() runs > before that test it sets slab_state to FULL but skips the unlinked cache, > which never got a sysfs entry, so sysfs_slab_release() calls kobject_put() > on a kobject that was never initialized: > > WARNING: lib/kobject.c:734 at kobject_put+0x64/0x2c0, CPU#1: kworker/u8:3/55 > kobject: '(null)' ((____ptrval____)): is not initialized, yet kobject_put() is being called. > refcount_t: underflow; use-after-free. > kobject_put+0x64/0x2c0 > sysfs_slab_release+0xc/0x20 > kmem_cache_destroy+0x104/0x1e0 > bioset_exit+0x13c/0x1e0 > disk_release+0x54/0x140 > put_disk+0x18/0x40 > floppy_async_init+0xbec/0xd10 > > The release-time test has run outside slab_mutex since at least v4.4 for > SLAB_TYPESAFE_BY_RCU caches, and since v6.0 for the others. Since v6.12 > the unlink-time test in kmem_cache_destroy() is a separate read of its > own, also after mutex_unlock(), so the two can disagree. Both tests ask > whether the cache has a kobject, which cache creation skips while > slab_state <= UP. UP is the state just below FULL, so a false sample > cannot skip a kobject_put() that was owed. > > Seen on sparc64 at boot, where the asynchronous floppy init tears down > its bio slab while the late initcalls are running. > > Sample slab_state once, under slab_mutex which slab_late_init() holds > when it sets FULL, and use the result for both the unlink and the > release. > > Fixes: d50d82faa0c9 ("slub: fix failure when we delete and create a slab cache") > Fixes: 4ec10268ed98 ("mm, slab: unlink slabinfo, sysfs and debugfs immediately") > Cc: stable@vger.kernel.org > Signed-off-by: Imre Kaloz > Reviewed-by: Jose A. Perez de Azpillaga > --- Looks good to me, Reviewed-by: Harry Yoo (Meta) I guess it's late to queue this to slab/for-next-fixes. Let's queue this to slab/for-next for 7.4-rc1. -- Cheers, Harry / Hyeonggon