From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id E9236C2EA; Mon, 9 Mar 2026 20:31:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773088272; cv=none; b=RTgN5ZgM5dpP1NrvoZNc+wtTD87tThyEiJdSeYfB3HjM7Ny2U/RIQCV8K8/HmJQj+g2s/c3xykPkWtUPar75TnfoZUj0fJ8ybUUcU/xUI8MSAXEZ/KMqv9UCw6zAkmSXiY6nXI25lGiH5cRXVgr8OkppXk5xkV1rZ+fF+UhbyqE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773088272; c=relaxed/simple; bh=LIBZ3t6qSs2lEqwdYFFVeDDtTa2MoTx83SBUaskuTn0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=dlNAA87HYB0tyqfS1RxchJPMKONbw0aBd40WlHyk2UTs++A7BqpBOZIAo7Mg1y0BaU7fW9kX8dfYz5sCMBfVLPi/Lpeg0vYnGRKVE2OKdIC1e3BI2V9zSMLoNUZFi1vxIWe3YnzRgd6jQNaaZxHbu/NQMSUSnuMUzc5GcVsxQ+Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 992821516; Mon, 9 Mar 2026 13:31:02 -0700 (PDT) Received: from arm.com (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C777A3F7BD; Mon, 9 Mar 2026 13:31:05 -0700 (PDT) Date: Mon, 9 Mar 2026 20:31:03 +0000 From: Catalin Marinas To: Harry Yoo Cc: "Vlastimil Babka (SUSE)" , Qing Wang , syzbot+cae7809e9dc1459e4e63@syzkaller.appspotmail.com, Liam.Howlett@oracle.com, akpm@linux-foundation.org, chao@kernel.org, jaegeuk@kernel.org, jannh@google.com, linkinjeon@kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, pfalcato@suse.de, sj1557.seo@samsung.com, syzkaller-bugs@googlegroups.com, vbabka@suse.cz, Hao Li Subject: Re: [syzbot] [mm?] [f2fs?] [exfat?] memory leak in __kfree_rcu_sheaf Message-ID: References: <698a26d3.050a0220.3b3015.007e.GAE@google.com> <20260302034102.3145719-1-wangqing7171@gmail.com> <20df8dd1-a32c-489d-8345-085d424a2f12@kernel.org> <925a916a-6dfb-48c0-985c-0bdfb96ebd26@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: On Mon, Mar 09, 2026 at 09:17:32PM +0900, Harry Yoo wrote: > On Fri, Mar 06, 2026 at 07:35:01PM +0000, Catalin Marinas wrote: > > [...snip...] > > > I wonder whether some early kmem_cache_node allocations like the ones in > > early_kmem_cache_node_alloc() are not tracked and then kmemleak cannot > > find n->barn. I got lost in the slub code, but something like this: > > This sounds plausible. Before sheaves, kmem_cache_node just maintained > a list of slabs. Because struct page (and struct slab overlaying on it) > is not tracked by kmemleak (as Vlastimil pointed out off-list), > not calling kmemleak_alloc() for kmem_cache_node was not a problem. > > But now it maintains barns and sheaves, > and they are tracked by kmemleak... We could simply add kmemleak_ignore(), especially as we don't need the data in these structures to be scanned. We can assume the slab allocator doesn't leak it's own data structures. But I couldn't figure out why kmemleak couldn't track down the pointer in the first place and any random kmemleak_alloc() I added did not solve it. > > -----------8<----------------------------------- > > diff --git a/mm/slub.c b/mm/slub.c > > index 0c906fefc31b..401557ff5487 100644 > > --- a/mm/slub.c > > +++ b/mm/slub.c > > @@ -7513,6 +7513,7 @@ static void early_kmem_cache_node_alloc(int node) > > slab->freelist = get_freepointer(kmem_cache_node, n); > > slab->inuse = 1; > > kmem_cache_node->node[node] = n; > > + kmemleak_alloc(n, sizeof(*n), 1, GFP_NOWAIT); > > init_kmem_cache_node(n, NULL); > > inc_slabs_node(kmem_cache_node, node, slab->objects); > > But this function is called for kmem_cache_node cache > (in kmem_cache_init()), even before kmemleak_init()? That's fine, kmemleak starts as enabled by default and tracks early allocations in a local mem_pool[] array. kmemleak_init() just initialises its kmem_caches for the long run. > kmem_cache and kmalloc caches should call kmemleak_alloc() when > allocating kmem_cache_node structures, but as they are also created > before kmemleak_init(), I doubt that's actually doing its job... It does. I just added a kmemleak_alloc() in create_kmalloc_cache() and kmemleak complained that the object from the kmem_cache_zalloc() is already registered. Of course, no stack trace saved for these early allocations but it does track them. > > -------------8<---------------------------------------- > > > > Another thing I noticed, not sure it's related but we should probably > > ignore an object once it has been passed to kvfree_call_rcu(), similar > > to what we do on the main path in this function. Also see commit > > 5f98fd034ca6 ("rcu: kmemleak: Ignore kmemleak false positives when > > RCU-freeing objects") when we added this kmemleak_ignore(). > > > > ---------8<----------------------------------- > > diff --git a/mm/slab_common.c b/mm/slab_common.c > > index d5a70a831a2a..73f4668d870d 100644 > > --- a/mm/slab_common.c > > +++ b/mm/slab_common.c > > @@ -1954,8 +1954,14 @@ void kvfree_call_rcu(struct rcu_head *head, void *ptr) > > if (!head) > > might_sleep(); > > > > - if (!IS_ENABLED(CONFIG_PREEMPT_RT) && kfree_rcu_sheaf(ptr)) > > + if (!IS_ENABLED(CONFIG_PREEMPT_RT) && kfree_rcu_sheaf(ptr)) { > > + /* > > + * The object is now queued for deferred freeing via an RCU > > + * sheaf. Tell kmemleak to ignore it. > > + */ > > + kmemleak_ignore(ptr); > > As Vlastimil pointed out off-list, we need to let kmemleak ignore > sheaves when they are submitted to call_rcu() and ideally undo > kmemleak_ignore() in __kfree_rcu_sheaf() when they are going to be reused. > > But looking at mm/kmemleak.c, undoing kmemleak_ignore() doesn't seem to > be a thing. If that's needed, something like below: ----------------------8<--------------------------------- diff --git a/Documentation/dev-tools/kmemleak.rst b/Documentation/dev-tools/kmemleak.rst index 7d784e03f3f9..da2c849d4735 100644 --- a/Documentation/dev-tools/kmemleak.rst +++ b/Documentation/dev-tools/kmemleak.rst @@ -163,6 +163,7 @@ See the include/linux/kmemleak.h header for the functions prototype. - ``kmemleak_not_leak`` - mark an object as not a leak - ``kmemleak_transient_leak`` - mark an object as a transient leak - ``kmemleak_ignore`` - do not scan or report an object as leak +- ``kmemleak_unignore`` - undo a previous kmemleak_ignore() - ``kmemleak_scan_area`` - add scan areas inside a memory block - ``kmemleak_no_scan`` - do not scan a memory block - ``kmemleak_erase`` - erase an old value in a pointer variable diff --git a/include/linux/kmemleak.h b/include/linux/kmemleak.h index fbd424b2abb1..4eec0560be09 100644 --- a/include/linux/kmemleak.h +++ b/include/linux/kmemleak.h @@ -28,6 +28,7 @@ extern void kmemleak_update_trace(const void *ptr) __ref; extern void kmemleak_not_leak(const void *ptr) __ref; extern void kmemleak_transient_leak(const void *ptr) __ref; extern void kmemleak_ignore(const void *ptr) __ref; +extern void kmemleak_unignore(const void *ptr, int min_count) __ref; extern void kmemleak_ignore_percpu(const void __percpu *ptr) __ref; extern void kmemleak_scan_area(const void *ptr, size_t size, gfp_t gfp) __ref; extern void kmemleak_no_scan(const void *ptr) __ref; @@ -104,6 +105,10 @@ static inline void kmemleak_ignore_percpu(const void __percpu *ptr) static inline void kmemleak_ignore(const void *ptr) { } + +static inline void kmemleak_unignore(const void *ptr, int min_count) +{ +} static inline void kmemleak_scan_area(const void *ptr, size_t size, gfp_t gfp) { } diff --git a/mm/kmemleak.c b/mm/kmemleak.c index d79acf5c5100..99b7ebd03737 100644 --- a/mm/kmemleak.c +++ b/mm/kmemleak.c @@ -1292,6 +1292,24 @@ void __ref kmemleak_ignore(const void *ptr) } EXPORT_SYMBOL(kmemleak_ignore); +/** + * kmemleak_unignore - undo a previous kmemleak_ignore() on an object + * @ptr: pointer to beginning of the object + * @min_count: minimum number of references the object must have to be + * considered a non-leak (see kmemleak_alloc() for details) + * + * Calling this function undoes a prior kmemleak_ignore() by restoring the + * given min_count, making the object visible to kmemleak again. + */ +void __ref kmemleak_unignore(const void *ptr, int min_count) +{ + pr_debug("%s(0x%px)\n", __func__, ptr); + + if (kmemleak_enabled && ptr && !IS_ERR(ptr)) + paint_ptr((unsigned long)ptr, min_count, 0); +} +EXPORT_SYMBOL(kmemleak_unignore); + /** * kmemleak_scan_area - limit the range to be scanned in an allocated object * @ptr: pointer to beginning or inside the object. This also ----------------------8<--------------------------------- -- Catalin