From nobody Mon Feb 9 15:25:40 2026 Received: from zeniv.linux.org.uk (zeniv.linux.org.uk [62.89.141.173]) (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 63C13500963; Sat, 10 Jan 2026 04:01:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=62.89.141.173 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768017664; cv=none; b=om30xKkfyD+/H20dwE6iSypC0q5l2Dhfwtzy2FBPaepOI7km6X/aZVFyFdvfzCrXGTf+wLVOsq1WoR/6Oq97OeuaQDPsPaDYybEwctBUDz3OznVJW1jJCZdggBUro10QPwO1iY0VSON0SnbFpWZFvzUTHEP2sXa7tRYCgCMRMss= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768017664; c=relaxed/simple; bh=FNJ/LAWDZhf/4UGECsNoVJF3S9MIQgpyO8vZJlbx1Wc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=RTx4sRFVTKbZByfSN4bUGGdQi/NSt0Nnj3H1sZ6pWM+T+uq2DVWqxcaWI8KnjBS9AwHdWRz/34YyKbOazA9up/ukYpS+L53qC+fMEtDe8LLlEgVKsDGv5Bf6qBpJE+WlHiV5CW6nsys2bK1GdPGhqVL7eu9jcP3Ddu1NoA5ogUU= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zeniv.linux.org.uk; spf=none smtp.mailfrom=ftp.linux.org.uk; dkim=pass (2048-bit key) header.d=linux.org.uk header.i=@linux.org.uk header.b=TFa5gVdr; arc=none smtp.client-ip=62.89.141.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zeniv.linux.org.uk Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=ftp.linux.org.uk Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linux.org.uk header.i=@linux.org.uk header.b="TFa5gVdr" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=linux.org.uk; s=zeniv-20220401; h=Sender:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From: Reply-To:Content-Type:Content-ID:Content-Description; bh=ISNZFsbhMluGOOgPJOf7PuXZbW/+Y33dgsD1DeUdNV0=; b=TFa5gVdrJvHVBG1sACtJpPQTOx +glfX5twmsJHBvGQUd7Lw6Y+eEtRTXV77LC0AUyJHDPFml5kDOFay7oyDroqQn4vCJRcljjNA0aSz +QxWiTMVa86jafeoaXLMOWXtREF0YYii1VtGCQNHJh1BFZtaezyAEKZpJWWDXIm0Ld71UF4NIazsu GqDPFmAj1U/RyGs0YUSxdga4Vb0FbVSPchaXbqR40LpZ96DTfeku9RnQvxIVIwt4DEl3yIAUpfWmI 4Ca+Fwlz7Q31GJeuKZ2e9DoUwKZLhy+hSK5pcPJPtymhmyfb1WBOr8Uia9RNWzOz5VlLooAzzSV/i JZInNl/g==; Received: from viro by zeniv.linux.org.uk with local (Exim 4.99 #2 (Red Hat Linux)) id 1veQB8-000000085ZD-1yqq; Sat, 10 Jan 2026 04:02:18 +0000 From: Al Viro To: linux-mm@kvack.org Cc: Vlastimil Babka , Harry Yoo , linux-fsdevel@vger.kernel.org, Linus Torvalds , Christian Brauner , Jan Kara , Mateusz Guzik , linux-kernel@vger.kernel.org Subject: [RFC PATCH 02/15] allow static-duration kmem_cache in modules Date: Sat, 10 Jan 2026 04:02:04 +0000 Message-ID: <20260110040217.1927971-3-viro@zeniv.linux.org.uk> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260110040217.1927971-1-viro@zeniv.linux.org.uk> References: <20260110040217.1927971-1-viro@zeniv.linux.org.uk> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Sender: Al Viro Content-Type: text/plain; charset="utf-8" We need to make sure that instance in a module will get to slab_kmem_cache_release() before the module data gets freed. That's only a problem on sysfs setups - otherwise it'll definitely be finished before kmem_cache_destroy() returns. Note that modules themselves have sysfs-exposed attributes, so a similar problem already exists there. That's dealt with by having mod_sysfs_teardown() wait for refcount of module->mkobj.kobj reaching zero. Let's make use of that - have static-duration-in-module kmem_cache instances grab a reference to that kobject upon setup and drop it in the end of slab_kmem_cache_release(). Let setup helpers store the kobjetct to be pinned in kmem_cache_args->owner (for preallocated; if somebody manually sets it for non-preallocated case, it'll be ignored). That would be &THIS_MODULE->mkobj.kobj for a module and NULL in built-in. If sysfs is enabled and we are dealing with preallocated instance, let create_cache() grab and stash that reference in kmem_cache->owner and let slab_kmem_cache_release() drop it instead of freeing kmem_cache instance. Signed-off-by: Al Viro --- include/linux/slab-static.h | 12 ++++++++---- include/linux/slab.h | 4 ++++ mm/slab.h | 1 + mm/slab_common.c | 16 ++++++++++++++-- 4 files changed, 27 insertions(+), 6 deletions(-) diff --git a/include/linux/slab-static.h b/include/linux/slab-static.h index 47b2220b4988..16d1564b4a4b 100644 --- a/include/linux/slab-static.h +++ b/include/linux/slab-static.h @@ -2,10 +2,7 @@ #ifndef _LINUX_SLAB_STATIC_H #define _LINUX_SLAB_STATIC_H =20 -#ifdef MODULE -#error "can't use that in modules" -#endif - +#include #include =20 /* same size and alignment as struct kmem_cache: */ @@ -13,9 +10,16 @@ struct kmem_cache_opaque { unsigned char opaque[KMEM_CACHE_SIZE]; } __aligned(KMEM_CACHE_ALIGN); =20 +#ifdef MODULE +#define THIS_MODULE_KOBJ &THIS_MODULE->mkobj.kobj +#else +#define THIS_MODULE_KOBJ NULL +#endif + #define __KMEM_CACHE_SETUP(cache, name, size, flags, ...) \ __kmem_cache_create_args((name), (size), \ &(struct kmem_cache_args) { \ + .owner =3D THIS_MODULE_KOBJ, \ .preallocated =3D (cache), \ __VA_ARGS__}, (flags)) =20 diff --git a/include/linux/slab.h b/include/linux/slab.h index f16c784148b4..dc1aeb14a12b 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -60,6 +60,7 @@ enum _slab_flag_bits { #ifdef CONFIG_SLAB_OBJ_EXT _SLAB_NO_OBJ_EXT, #endif + _SLAB_PREALLOCATED, _SLAB_FLAGS_LAST_BIT }; =20 @@ -244,6 +245,8 @@ enum _slab_flag_bits { #define SLAB_NO_OBJ_EXT __SLAB_FLAG_UNUSED #endif =20 +#define SLAB_PREALLOCATED __SLAB_FLAG_BIT(_SLAB_PREALLOCATED) + /* * ZERO_SIZE_PTR will be returned for zero sized kmalloc requests. * @@ -373,6 +376,7 @@ struct kmem_cache_args { */ unsigned int sheaf_capacity; struct kmem_cache *preallocated; + struct kobject *owner; }; =20 struct kmem_cache *__kmem_cache_create_args(const char *name, diff --git a/mm/slab.h b/mm/slab.h index e767aa7e91b0..9ff9a0a3b164 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -249,6 +249,7 @@ struct kmem_cache { struct list_head list; /* List of slab caches */ #ifdef CONFIG_SYSFS struct kobject kobj; /* For sysfs */ + struct kobject *owner; /* keep that pinned while alive */ #endif #ifdef CONFIG_SLAB_FREELIST_HARDENED unsigned long random; diff --git a/mm/slab_common.c b/mm/slab_common.c index 81a413b44afb..a854e6872acd 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -245,6 +245,12 @@ static struct kmem_cache *create_cache(const char *nam= e, kmem_cache_free(kmem_cache, s); return ERR_PTR(err); } +#ifdef CONFIG_SYSFS + if (flags & SLAB_PREALLOCATED) { + s->owner =3D args->owner; + kobject_get(s->owner); + } +#endif s->refcount =3D 1; list_add(&s->list, &slab_caches); return s; @@ -322,7 +328,7 @@ struct kmem_cache *__kmem_cache_create_args(const char = *name, args->usersize =3D args->useroffset =3D 0; =20 if (args->preallocated) - flags |=3D SLAB_NO_MERGE; + flags |=3D SLAB_NO_MERGE | SLAB_PREALLOCATED; =20 if (!args->usersize && !args->sheaf_capacity) s =3D __kmem_cache_alias(name, object_size, args->align, flags, @@ -481,7 +487,13 @@ void slab_kmem_cache_release(struct kmem_cache *s) { __kmem_cache_release(s); kfree_const(s->name); - kmem_cache_free(kmem_cache, s); + if (!(s->flags & SLAB_PREALLOCATED)) { + kmem_cache_free(kmem_cache, s); + return; + } +#ifdef CONFIG_SYSFS + kobject_put(s->owner); +#endif } =20 void kmem_cache_destroy(struct kmem_cache *s) --=20 2.47.3