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[23.128.96.18]) by mx.google.com with ESMTP id b10si4861651edu.535.2020.12.11.03.43.04; Fri, 11 Dec 2020 03:43:27 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=k20201202 header.b=NY5yd4Fa; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2405252AbgLKDfO (ORCPT + 99 others); Thu, 10 Dec 2020 22:35:14 -0500 Received: from mail.kernel.org ([198.145.29.99]:54442 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2395130AbgLKDel (ORCPT ); Thu, 10 Dec 2020 22:34:41 -0500 Date: Thu, 10 Dec 2020 19:33:59 -0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1607657639; bh=Kg5oDTUTdbm/9uHfD0T6Su7jZUCRDXSrX9Du+hLnf3M=; h=From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=NY5yd4Fat9uN3QnquDugNs300C+v8HRDCM7h0udvqkOLK/aLjTOrLQSvZjFzKD6Uj ecHH0jKalLC1IHgu6fMKl0MUDaMK7HgCfOtgGnKSBVqLA8H2vrLcf4R7xdMWKPxww2 CcRpizeOAGUt1dgkb1Ut5+TbBU4yYvRQVggO0hw8rRPnNJf7PIKO3m7eC8ZeGRuxLb GMXGQZM5MThbgrBn89LSh1/xGWrtOa5tCelghKZiOfqPekpqXTiolWY82yUKpU74N1 9ps2vy8uxWKYHgtR7r1R+9mQ8dRT6RGCQFU3n/pL15iNKAtvnOdqwXYwmaBLPhijie AO83EUMsn7TiA== From: "Paul E. McKenney" To: Joonsoo Kim Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, andrii@kernel.org, Christoph Lameter , Pekka Enberg , David Rientjes , linux-mm@kvack.org Subject: Re: [PATCH v3 sl-b 1/6] mm: Add mem_dump_obj() to print source of memory block Message-ID: <20201211033359.GD2657@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20201211011907.GA16110@paulmck-ThinkPad-P72> <20201211012003.16473-1-paulmck@kernel.org> <20201211022205.GA11631@js1304-desktop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201211022205.GA11631@js1304-desktop> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 11, 2020 at 11:22:10AM +0900, Joonsoo Kim wrote: > On Thu, Dec 10, 2020 at 05:19:58PM -0800, paulmck@kernel.org wrote: > > From: "Paul E. McKenney" > > > > There are kernel facilities such as per-CPU reference counts that give > > error messages in generic handlers or callbacks, whose messages are > > unenlightening. In the case of per-CPU reference-count underflow, this > > is not a problem when creating a new use of this facility because in that > > case the bug is almost certainly in the code implementing that new use. > > However, trouble arises when deploying across many systems, which might > > exercise corner cases that were not seen during development and testing. > > Here, it would be really nice to get some kind of hint as to which of > > several uses the underflow was caused by. > > > > This commit therefore exposes a mem_dump_obj() function that takes > > a pointer to memory (which must still be allocated if it has been > > dynamically allocated) and prints available information on where that > > memory came from. This pointer can reference the middle of the block as > > well as the beginning of the block, as needed by things like RCU callback > > functions and timer handlers that might not know where the beginning of > > the memory block is. These functions and handlers can use mem_dump_obj() > > to print out better hints as to where the problem might lie. > > > > The information printed can depend on kernel configuration. For example, > > the allocation return address can be printed only for slab and slub, > > and even then only when the necessary debug has been enabled. For slab, > > build with CONFIG_DEBUG_SLAB=y, and either use sizes with ample space > > to the next power of two or use the SLAB_STORE_USER when creating the > > kmem_cache structure. For slub, build with CONFIG_SLUB_DEBUG=y and > > boot with slub_debug=U, or pass SLAB_STORE_USER to kmem_cache_create() > > if more focused use is desired. Also for slub, use CONFIG_STACKTRACE > > to enable printing of the allocation-time stack trace. > > > > Cc: Christoph Lameter > > Cc: Pekka Enberg > > Cc: David Rientjes > > Cc: Joonsoo Kim > > Cc: Andrew Morton > > Cc: > > Reported-by: Andrii Nakryiko > > [ paulmck: Convert to printing and change names per Joonsoo Kim. ] > > [ paulmck: Move slab definition per Stephen Rothwell and kbuild test robot. ] > > [ paulmck: Handle CONFIG_MMU=n case where vmalloc() is kmalloc(). ] > > [ paulmck: Apply Vlastimil Babka feedback on slab.c kmem_provenance(). ] > > Signed-off-by: Paul E. McKenney > > --- > > include/linux/mm.h | 2 ++ > > include/linux/slab.h | 2 ++ > > mm/slab.c | 20 ++++++++++++++ > > mm/slab.h | 12 +++++++++ > > mm/slab_common.c | 74 ++++++++++++++++++++++++++++++++++++++++++++++++++++ > > mm/slob.c | 6 +++++ > > mm/slub.c | 36 +++++++++++++++++++++++++ > > mm/util.c | 24 +++++++++++++++++ > > 8 files changed, 176 insertions(+) > > > > diff --git a/include/linux/mm.h b/include/linux/mm.h > > index ef360fe..1eea266 100644 > > --- a/include/linux/mm.h > > +++ b/include/linux/mm.h > > @@ -3153,5 +3153,7 @@ unsigned long wp_shared_mapping_range(struct address_space *mapping, > > > > extern int sysctl_nr_trim_pages; > > > > +void mem_dump_obj(void *object); > > + > > #endif /* __KERNEL__ */ > > #endif /* _LINUX_MM_H */ > > diff --git a/include/linux/slab.h b/include/linux/slab.h > > index dd6897f..169b511 100644 > > --- a/include/linux/slab.h > > +++ b/include/linux/slab.h > > @@ -186,6 +186,8 @@ void kfree(const void *); > > void kfree_sensitive(const void *); > > size_t __ksize(const void *); > > size_t ksize(const void *); > > +bool kmem_valid_obj(void *object); > > +void kmem_dump_obj(void *object); > > > > #ifdef CONFIG_HAVE_HARDENED_USERCOPY_ALLOCATOR > > void __check_heap_object(const void *ptr, unsigned long n, struct page *page, > > diff --git a/mm/slab.c b/mm/slab.c > > index b111356..66f00ad 100644 > > --- a/mm/slab.c > > +++ b/mm/slab.c > > @@ -3633,6 +3633,26 @@ void *__kmalloc_node_track_caller(size_t size, gfp_t flags, > > EXPORT_SYMBOL(__kmalloc_node_track_caller); > > #endif /* CONFIG_NUMA */ > > > > +void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page) > > +{ > > + struct kmem_cache *cachep; > > + unsigned int objnr; > > + void *objp; > > + > > + kpp->kp_ptr = object; > > + kpp->kp_page = page; > > + cachep = page->slab_cache; > > + kpp->kp_slab_cache = cachep; > > + objp = object - obj_offset(cachep); > > + kpp->kp_data_offset = obj_offset(cachep); > > + page = virt_to_head_page(objp); > > + objnr = obj_to_index(cachep, page, objp); > > + objp = index_to_obj(cachep, page, objnr); > > + kpp->kp_objp = objp; > > + if (DEBUG && cachep->flags & SLAB_STORE_USER) > > + kpp->kp_ret = *dbg_userword(cachep, objp); > > +} > > + > > /** > > * __do_kmalloc - allocate memory > > * @size: how many bytes of memory are required. > > diff --git a/mm/slab.h b/mm/slab.h > > index 6d7c6a5..0dc705b 100644 > > --- a/mm/slab.h > > +++ b/mm/slab.h > > @@ -630,4 +630,16 @@ static inline bool slab_want_init_on_free(struct kmem_cache *c) > > return false; > > } > > > > +#define KS_ADDRS_COUNT 16 > > +struct kmem_obj_info { > > + void *kp_ptr; > > + struct page *kp_page; > > + void *kp_objp; > > + unsigned long kp_data_offset; > > + struct kmem_cache *kp_slab_cache; > > + void *kp_ret; > > + void *kp_stack[KS_ADDRS_COUNT]; > > +}; > > +void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page); > > + > > #endif /* MM_SLAB_H */ > > diff --git a/mm/slab_common.c b/mm/slab_common.c > > index f9ccd5d..df2e203 100644 > > --- a/mm/slab_common.c > > +++ b/mm/slab_common.c > > @@ -536,6 +536,80 @@ bool slab_is_available(void) > > return slab_state >= UP; > > } > > > > +/** > > + * kmem_valid_obj - does the pointer reference a valid slab object? > > + * @object: pointer to query. > > + * > > + * Return: %true if the pointer is to a not-yet-freed object from > > + * kmalloc() or kmem_cache_alloc(), either %true or %false if the pointer > > + * is to an already-freed object, and %false otherwise. > > + */ > > +bool kmem_valid_obj(void *object) > > +{ > > + struct page *page; > > + > > + if (!virt_addr_valid(object)) > > + return false; > > + page = virt_to_head_page(object); > > + return PageSlab(page); > > +} > > + > > +/** > > + * kmem_dump_obj - Print available slab provenance information > > + * @object: slab object for which to find provenance information. > > + * > > + * This function uses pr_cont(), so that the caller is expected to have > > + * printed out whatever preamble is appropriate. The provenance information > > + * depends on the type of object and on how much debugging is enabled. > > + * For a slab-cache object, the fact that it is a slab object is printed, > > + * and, if available, the slab name, return address, and stack trace from > > + * the allocation of that object. > > + * > > + * This function will splat if passed a pointer to a non-slab object. > > + * If you are not sure what type of object you have, you should instead > > + * use mem_dump_obj(). > > + */ > > +void kmem_dump_obj(void *object) > > +{ > > + char *cp = IS_ENABLED(CONFIG_MMU) ? "" : "/vmalloc"; > > + int i; > > + struct page *page; > > + unsigned long ptroffset; > > + struct kmem_obj_info kp = { }; > > + > > + if (WARN_ON_ONCE(!virt_addr_valid(object))) > > + return; > > + page = virt_to_head_page(object); > > + if (WARN_ON_ONCE(!PageSlab(page))) { > > + pr_cont(" non-slab memory.\n"); > > + return; > > + } > > + kmem_obj_info(&kp, object, page); > > + if (kp.kp_slab_cache) > > + pr_cont(" slab%s %s", cp, kp.kp_slab_cache->name); > > + else > > + pr_cont(" slab%s", cp); > > + if (kp.kp_objp) > > + pr_cont(" start %px", kp.kp_objp); > > + if (kp.kp_data_offset) > > + pr_cont(" data offset %lu", kp.kp_data_offset); > > I don't check the code deeply but kp_data_offset could be 0 in normal > situation. Is it intentional not to print a message in this case? Yes, so that it tells you of the offset only if it is non-zero, which as you say happens only if certain debugging options are enabled. Easy to print it unconditionally if that is preferred! > > + if (kp.kp_objp) { > > + ptroffset = ((char *)object - (char *)kp.kp_objp) - kp.kp_data_offset; > > + pr_cont(" pointer offset %lu", ptroffset); > > + } > > + if (kp.kp_slab_cache && kp.kp_slab_cache->usersize) > > + pr_cont(" size %u", kp.kp_slab_cache->usersize); > > + if (kp.kp_ret) > > + pr_cont(" allocated at %pS\n", kp.kp_ret); > > + else > > + pr_cont("\n"); > > + for (i = 0; i < ARRAY_SIZE(kp.kp_stack); i++) { > > + if (!kp.kp_stack[i]) > > + break; > > + pr_info(" %pS\n", kp.kp_stack[i]); > > + } > > +} > > + > > #ifndef CONFIG_SLOB > > /* Create a cache during boot when no slab services are available yet */ > > void __init create_boot_cache(struct kmem_cache *s, const char *name, > > diff --git a/mm/slob.c b/mm/slob.c > > index 7cc9805..2ed1de2 100644 > > --- a/mm/slob.c > > +++ b/mm/slob.c > > @@ -461,6 +461,12 @@ static void slob_free(void *block, int size) > > spin_unlock_irqrestore(&slob_lock, flags); > > } > > > > +void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page) > > +{ > > + kpp->kp_ptr = object; > > + kpp->kp_page = page; > > +} > > + > > /* > > * End of slob allocator proper. Begin kmem_cache_alloc and kmalloc frontend. > > */ > > diff --git a/mm/slub.c b/mm/slub.c > > index b30be23..0459d2a 100644 > > --- a/mm/slub.c > > +++ b/mm/slub.c > > @@ -3918,6 +3918,42 @@ int __kmem_cache_shutdown(struct kmem_cache *s) > > return 0; > > } > > > > +void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page) > > +{ > > +#ifdef CONFIG_SLUB_DEBUG > > We can get some infos even if CONFIG_SLUB_DEBUG isn't defined. > Please move them out. I guess since I worry about CONFIG_MMU=n it only makes sense to also worry about CONFIG_SLUB_DEBUG=n. Fix update. Thanx, Paul