From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8D3BB486420; Wed, 14 Oct 2026 19:46:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792007218; cv=none; b=bKSrgs5DI4v9SXJ7xUw/lx+YsrYATyymSHxdhCXJr0Ezc4NaWV+AS6dN9731tvck7zV8/ex7inxwAJx+88cWMSV5s/dd7aoLEe+1ZOD9QQ5YQGxdD6He5P/x7+14bBQ/BIrGV1MG/jdAX/CZuVBIAG0yTJWCapA/1pobTs/iMmg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792007218; c=relaxed/simple; bh=F8iUNDa8xve1BSXQ6Tye39xGf3MOB6x7ueXyLnS6mfg=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=neAK8zjYM9rADJuCZPEYMe+e1p2cBIKxMT+CCZWHqDqQJPu9etEvumrVOB37tTEhC/OrwF2Tv6+1iTU0zMkoo6BFXogNXRftbA8dG6yCbUcWPm1SpIMc6MFfJsm5zP/yOsV6s0jsoobogxe6MlVv/KuixIqiReo1JRWR6dVtLfM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=RmQVoIwa; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="RmQVoIwa" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 843F91F000C4; Wed, 14 Oct 2026 19:46:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792007216; bh=VkzoqxTdzmAg593ZpIds3NlLUMIFMc0b1AE/YCVZDWw=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=RmQVoIwaX4F+m+QOTfBZ/BEap2Ci3CR8vUwT+k50W7Jgus1MTHRpWoDCeRk3szKas uzosIYzkaiam6ix1S/hWjqoS0TxPoO4a78Ix3OO/QlCm1KxycxhrmJY+w49cFxMjwl sk3k3ikgGrwEwt4FTM8SfDW2xPJnk3Dx29n1Nde0Q2+khRQ3bZthoThKsbDyY9fCQF V3HBMdhNdz95Pk/NV2mftbwGl26FI4HxJ+7kXD1zqiIVSFJf7Yhh0vv+10/yJfQq8L Ba+aRlqD7WHu3E5lC8suYwgKJ6fMw9JkM3+Njs0J4n1Tcuzpnv7F1mM/eacKy4v12z hrI8yQ7+5y9kg== Date: Wed, 14 Oct 2026 20:46:53 +0100 From: Harry Yoo To: Imre Kaloz Cc: Vlastimil Babka , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , Jann Horn , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, "Jose A . 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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261014150844.8536-1-kaloz@kernel.org> 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