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Thu, 01 Apr 2021 02:16:42 -0700 (PDT) Received: from elver.google.com ([2a00:79e0:15:13:898b:d931:3b:8aee]) by smtp.gmail.com with ESMTPSA id o2sm7394805wmr.10.2021.04.01.02.16.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Apr 2021 02:16:41 -0700 (PDT) Date: Thu, 1 Apr 2021 11:16:36 +0200 From: Marco Elver To: glittao@gmail.com Cc: cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, vbabka@suse.cz, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kunit-dev@googlegroups.com Subject: Re: [PATCH v3 1/2] kunit: add a KUnit test for SLUB debugging functionality Message-ID: References: <20210331085156.5028-1-glittao@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210331085156.5028-1-glittao@gmail.com> User-Agent: Mutt/2.0.5 (2021-01-21) X-Stat-Signature: pexbfoytxg86oz8koqcg3bf4ys71euk4 X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 6907680192E1 Received-SPF: none (google.com>: No applicable sender policy available) receiver=imf08; identity=mailfrom; envelope-from=""; helo=mail-wm1-f52.google.com; client-ip=209.85.128.52 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1617268602-287784 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: [Note, if you'd like me to see future versions, please Cc me, otherwise it's unlikely I see it in time. Also add kunit-dev@googlegroups.com if perhaps a KUnit dev should have another look, too.] On Wed, Mar 31, 2021 at 10:51AM +0200, glittao@gmail.com wrote: > From: Oliver Glitta > > SLUB has resiliency_test() function which is hidden behind #ifdef > SLUB_RESILIENCY_TEST that is not part of Kconfig, so nobody > runs it. KUnit should be a proper replacement for it. > > Try changing byte in redzone after allocation and changing > pointer to next free node, first byte, 50th byte and redzone > byte. Check if validation finds errors. > > There are several differences from the original resiliency test: > Tests create own caches with known state instead of corrupting > shared kmalloc caches. > > The corruption of freepointer uses correct offset, the original > resiliency test got broken with freepointer changes. > > Scratch changing random byte test, because it does not have > meaning in this form where we need deterministic results. > > Add new option CONFIG_SLUB_KUNIT_TEST in Kconfig. > > Add a counter field "errors" to struct kmem_cache to count number > of errors detected in cache. > > Silence bug report in SLUB test. Add SLAB_SILENT_ERRORS debug flag. > Add SLAB_SILENT_ERRORS flag to SLAB_NEVER_MERGE, SLAB_DEBUG_FLAGS, > SLAB_FLAGS_PERMITTED macros. > > Signed-off-by: Oliver Glitta > --- > Changes since v2 > > Use bit operation & instead of logical && as reported by kernel test > robot and Dan Carpenter > > Changes since v1 > > Conversion from kselftest to KUnit test suggested by Marco Elver. > Error silencing. > Error counting improvements. > > include/linux/slab.h | 2 + > include/linux/slub_def.h | 2 + > lib/Kconfig.debug | 5 ++ > lib/Makefile | 1 + > lib/test_slub.c | 124 +++++++++++++++++++++++++++++++++++++++ > mm/slab.h | 7 ++- > mm/slab_common.c | 2 +- > mm/slub.c | 64 +++++++++++++------- > 8 files changed, 184 insertions(+), 23 deletions(-) > create mode 100644 lib/test_slub.c > > diff --git a/include/linux/slab.h b/include/linux/slab.h > index 7ae604076767..ed1a5a64d028 100644 > --- a/include/linux/slab.h > +++ b/include/linux/slab.h > @@ -25,6 +25,8 @@ > */ > /* DEBUG: Perform (expensive) checks on alloc/free */ > #define SLAB_CONSISTENCY_CHECKS ((slab_flags_t __force)0x00000100U) > +/* DEBUG: Silent bug reports */ > +#define SLAB_SILENT_ERRORS ((slab_flags_t __force)0x00000200U) This flag wouldn't be necessary if you do the design using kunit_resource (see below). (But perhaps I missed a conversation that said that this flag is generally useful, but if so, it should probably be in a separate patch justifying why it is required beyond the test.) > /* DEBUG: Red zone objs in a cache */ > #define SLAB_RED_ZONE ((slab_flags_t __force)0x00000400U) > /* DEBUG: Poison objects */ > diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h > index dcde82a4434c..e4b51bb5bb83 100644 > --- a/include/linux/slub_def.h > +++ b/include/linux/slub_def.h > @@ -133,6 +133,8 @@ struct kmem_cache { > unsigned int usersize; /* Usercopy region size */ > > struct kmem_cache_node *node[MAX_NUMNODES]; > + > + int errors; /* Number of errors in cache */ So, I think it's bad design to add a new field 'errors', just for the test. This will increase kmem_cache size for all builds, which is unnecessary. Is there use to retrieve 'errors' elsewhere? While you could guard this with #ifdef CONFIG_SLUB_DEBUG or so, there's a better design option if this is just for the KUnit test's benefit: use kunit_resource. The way it'd work is that for each test (you can add a common init function) you add a named resource, in this case just an 'int' I guess, that slab would be able to retrieve if this test is being run. In the test somewhere, you could add something like this: static struct kunit_resource resource; static int slab_errors; .......... static int test_init(struct kunit *test) { slab_errors = 0; kunit_add_named_resource(test, NULL, NULL, &resource, "slab_errors", &slab_errors); return 0; } ...... tests now check slab_errors ..... and then in slub.c you'd have: #if IS_ENABLED(CONFIG_KUNIT) static bool slab_add_kunit_errors(void) { struct kunit_resource *resource; if (likely(!current->kunit_test)) return false; resource = kunit_find_named_resource(current->kunit_test, "slab_errors"); if (!resource) return false; (*(int *)resource->data)++; kunit_put_resource(resource); } #else static inline bool slab_add_kunit_errors(void) { return false; } #endif And anywhere you want to increase the error count, you'd call slab_add_kunit_errors(). Another benefit of this approach is that if KUnit is disabled, there is zero overhead and no additional code generated (vs. the current approach). > }; > > #ifdef CONFIG_SLUB_CPU_PARTIAL > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > index 2779c29d9981..e0dec830c269 100644 > --- a/lib/Kconfig.debug > +++ b/lib/Kconfig.debug > @@ -2371,6 +2371,11 @@ config BITS_TEST > > If unsure, say N. > > +config SLUB_KUNIT_TEST > + tristate "KUnit Test for SLUB cache error detection" if !KUNIT_ALL_TESTS > + depends on SLUB_DEBUG && KUNIT > + default KUNIT_ALL_TESTS Help text please. > + > config TEST_UDELAY > tristate "udelay test driver" > help > diff --git a/lib/Makefile b/lib/Makefile > index b5307d3eec1a..e1eb986c0e87 100644 > --- a/lib/Makefile > +++ b/lib/Makefile > @@ -352,5 +352,6 @@ obj-$(CONFIG_LIST_KUNIT_TEST) += list-test.o > obj-$(CONFIG_LINEAR_RANGES_TEST) += test_linear_ranges.o > obj-$(CONFIG_BITS_TEST) += test_bits.o > obj-$(CONFIG_CMDLINE_KUNIT_TEST) += cmdline_kunit.o > +obj-$(CONFIG_SLUB_KUNIT_TEST) += test_slub.o Any reason to not name this slub_kunit.c? This is a new test, and it could follow the naming convention of the other KUnit tests. Some of it is also documented: https://www.kernel.org/doc/html/latest/dev-tools/kunit/style.html > obj-$(CONFIG_GENERIC_LIB_DEVMEM_IS_ALLOWED) += devmem_is_allowed.o > diff --git a/lib/test_slub.c b/lib/test_slub.c > new file mode 100644 > index 000000000000..4f8ea3c7d867 > --- /dev/null > +++ b/lib/test_slub.c > @@ -0,0 +1,124 @@ > +// SPDX-License-Identifier: GPL-2.0 > +#include > +#include > +#include > +#include > +#include > +#include "../mm/slab.h" > + > + > +static void test_clobber_zone(struct kunit *test) > +{ > + struct kmem_cache *s = kmem_cache_create("TestSlub_RZ_alloc", 64, 0, > + SLAB_RED_ZONE | SLAB_SILENT_ERRORS, NULL); > + u8 *p = kmem_cache_alloc(s, GFP_KERNEL); > + > + p[64] = 0x12; > + > + validate_slab_cache(s); > + KUNIT_EXPECT_EQ(test, 1, s->errors); > + > + kmem_cache_free(s, p); > + kmem_cache_destroy(s); > +} > + > +static void test_next_pointer(struct kunit *test) > +{ > + struct kmem_cache *s = kmem_cache_create("TestSlub_next_ptr_free", 64, 0, > + SLAB_POISON | SLAB_SILENT_ERRORS, NULL); > + u8 *p = kmem_cache_alloc(s, GFP_KERNEL); > + unsigned long tmp; > + unsigned long *ptr_addr; > + > + kmem_cache_free(s, p); > + > + ptr_addr = (unsigned long *)(p + s->offset); > + tmp = *ptr_addr; > + p[s->offset] = 0x12; > + > + /* > + * Expecting two errors. > + * One for the corrupted freechain and the other one for the wrong > + * count of objects in use. > + */ > + validate_slab_cache(s); > + KUNIT_EXPECT_EQ(test, 2, s->errors); > + > + /* > + * Try to repair corrupted freepointer. > + * Still expecting one error for the wrong count of objects in use. > + */ > + *ptr_addr = tmp; > + > + validate_slab_cache(s); > + KUNIT_EXPECT_EQ(test, 1, s->errors); > + > + /* > + * Previous validation repaired the count of objects in use. > + * Now expecting no error. > + */ > + validate_slab_cache(s); > + KUNIT_EXPECT_EQ(test, 0, s->errors); > + > + kmem_cache_destroy(s); > +} > + > +static void test_first_word(struct kunit *test) > +{ > + struct kmem_cache *s = kmem_cache_create("TestSlub_1th_word_free", 64, 0, > + SLAB_POISON | SLAB_SILENT_ERRORS, NULL); > + u8 *p = kmem_cache_alloc(s, GFP_KERNEL); > + > + kmem_cache_free(s, p); > + *p = 0x78; > + > + validate_slab_cache(s); > + KUNIT_EXPECT_EQ(test, 1, s->errors); > + > + kmem_cache_destroy(s); > +} > + > +static void test_clobber_50th_byte(struct kunit *test) > +{ > + struct kmem_cache *s = kmem_cache_create("TestSlub_50th_word_free", 64, 0, > + SLAB_POISON | SLAB_SILENT_ERRORS, NULL); > + u8 *p = kmem_cache_alloc(s, GFP_KERNEL); > + > + kmem_cache_free(s, p); > + p[50] = 0x9a; > + > + validate_slab_cache(s); > + KUNIT_EXPECT_EQ(test, 1, s->errors); > + kmem_cache_destroy(s); > +} > + > +static void test_clobber_redzone_free(struct kunit *test) > +{ > + struct kmem_cache *s = kmem_cache_create("TestSlub_RZ_free", 64, 0, > + SLAB_RED_ZONE | SLAB_SILENT_ERRORS, NULL); > + u8 *p = kmem_cache_alloc(s, GFP_KERNEL); > + > + kmem_cache_free(s, p); > + p[64] = 0xab; > + > + validate_slab_cache(s); > + KUNIT_EXPECT_EQ(test, 1, s->errors); > + kmem_cache_destroy(s); > +} > + > +static struct kunit_case test_cases[] = { > + KUNIT_CASE(test_clobber_zone), > + KUNIT_CASE(test_next_pointer), > + KUNIT_CASE(test_first_word), > + KUNIT_CASE(test_clobber_50th_byte), > + KUNIT_CASE(test_clobber_redzone_free), > + {} > +}; > + > +static struct kunit_suite test_suite = { > + .name = "slub_test", > + .test_cases = test_cases, Here you could add a .init = test_init, or so, if you go with the kunit_resource design. > +}; > +kunit_test_suite(test_suite); > + > +MODULE_LICENSE("GPL"); > diff --git a/mm/slab.h b/mm/slab.h > index 076582f58f68..382507b6cab9 100644 > --- a/mm/slab.h > +++ b/mm/slab.h > @@ -134,7 +134,8 @@ static inline slab_flags_t kmem_cache_flags(unsigned int object_size, > #define SLAB_DEBUG_FLAGS (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER) > #elif defined(CONFIG_SLUB_DEBUG) > #define SLAB_DEBUG_FLAGS (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER | \ > - SLAB_TRACE | SLAB_CONSISTENCY_CHECKS) > + SLAB_TRACE | SLAB_CONSISTENCY_CHECKS | \ > + SLAB_SILENT_ERRORS) > #else > #define SLAB_DEBUG_FLAGS (0) > #endif > @@ -164,7 +165,8 @@ static inline slab_flags_t kmem_cache_flags(unsigned int object_size, > SLAB_NOLEAKTRACE | \ > SLAB_RECLAIM_ACCOUNT | \ > SLAB_TEMPORARY | \ > - SLAB_ACCOUNT) > + SLAB_ACCOUNT | \ > + SLAB_SILENT_ERRORS) > > bool __kmem_cache_empty(struct kmem_cache *); > int __kmem_cache_shutdown(struct kmem_cache *); > @@ -215,6 +217,7 @@ DECLARE_STATIC_KEY_TRUE(slub_debug_enabled); > DECLARE_STATIC_KEY_FALSE(slub_debug_enabled); > #endif > extern void print_tracking(struct kmem_cache *s, void *object); > +long validate_slab_cache(struct kmem_cache *s); > #else > static inline void print_tracking(struct kmem_cache *s, void *object) > { > diff --git a/mm/slab_common.c b/mm/slab_common.c > index 88e833986332..239c9095e7ea 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -55,7 +55,7 @@ static DECLARE_WORK(slab_caches_to_rcu_destroy_work, > */ > #define SLAB_NEVER_MERGE (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER | \ > SLAB_TRACE | SLAB_TYPESAFE_BY_RCU | SLAB_NOLEAKTRACE | \ > - SLAB_FAILSLAB | kasan_never_merge()) > + SLAB_FAILSLAB | SLAB_SILENT_ERRORS | kasan_never_merge()) > > #define SLAB_MERGE_SAME (SLAB_RECLAIM_ACCOUNT | SLAB_CACHE_DMA | \ > SLAB_CACHE_DMA32 | SLAB_ACCOUNT) > diff --git a/mm/slub.c b/mm/slub.c > index 3021ce9bf1b3..7083e89432d0 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -673,14 +673,16 @@ static void slab_bug(struct kmem_cache *s, char *fmt, ...) > > static void slab_fix(struct kmem_cache *s, char *fmt, ...) > { > - struct va_format vaf; > - va_list args; > - > - va_start(args, fmt); > - vaf.fmt = fmt; > - vaf.va = &args; > - pr_err("FIX %s: %pV\n", s->name, &vaf); > - va_end(args); > + if (!(s->flags & SLAB_SILENT_ERRORS)) { This style of guarding causes lots of line diffs. Instead, if the whole function is to be skipped, please prefer: if (skip_things_if_true) return; instead of if (!skip_things_if_true) { ... } here and everywhere else. Specifically, for the kunit_resource design, this would simply become: if (slab_add_kunit_errors()) return; Meaning that whenever a KUnit test has a resource "slab_errors", no messages are printed -- otherwise it'll always print a message. > + struct va_format vaf; > + va_list args; > + > + va_start(args, fmt); > + vaf.fmt = fmt; > + vaf.va = &args; > + pr_err("FIX %s: %pV\n", s->name, &vaf); > + va_end(args); > + } > } > > static bool freelist_corrupted(struct kmem_cache *s, struct page *page, > @@ -739,8 +741,10 @@ static void print_trailer(struct kmem_cache *s, struct page *page, u8 *p) > void object_err(struct kmem_cache *s, struct page *page, > u8 *object, char *reason) > { > - slab_bug(s, "%s", reason); > - print_trailer(s, page, object); > + if (!(s->flags & SLAB_SILENT_ERRORS)) { > + slab_bug(s, "%s", reason); > + print_trailer(s, page, object); > + } > } > > static __printf(3, 4) void slab_err(struct kmem_cache *s, struct page *page, > @@ -752,9 +756,11 @@ static __printf(3, 4) void slab_err(struct kmem_cache *s, struct page *page, > va_start(args, fmt); > vsnprintf(buf, sizeof(buf), fmt, args); > va_end(args); > - slab_bug(s, "%s", buf); > - print_page_info(page); > - dump_stack(); > + if (!(s->flags & SLAB_SILENT_ERRORS)) { > + slab_bug(s, "%s", buf); > + print_page_info(page); > + dump_stack(); > + } > } > > static void init_object(struct kmem_cache *s, void *object, u8 val) > @@ -798,11 +804,13 @@ static int check_bytes_and_report(struct kmem_cache *s, struct page *page, > while (end > fault && end[-1] == value) > end--; > > - slab_bug(s, "%s overwritten", what); > - pr_err("INFO: 0x%p-0x%p @offset=%tu. First byte 0x%x instead of 0x%x\n", > + if (!(s->flags & SLAB_SILENT_ERRORS)) { > + slab_bug(s, "%s overwritten", what); > + pr_err("INFO: 0x%p-0x%p @offset=%tu. First byte 0x%x instead of 0x%x\n", > fault, end - 1, fault - addr, > fault[0], value); > - print_trailer(s, page, object); > + print_trailer(s, page, object); > + } > > restore_bytes(s, what, value, fault, end); > return 0; > @@ -964,6 +972,7 @@ static int check_slab(struct kmem_cache *s, struct page *page) > > if (!PageSlab(page)) { > slab_err(s, page, "Not a valid slab page"); > + s->errors += 1; So to me it looks like errors is set whenever there's a slab_err() or slab_fix() call. So why not move setting that an error occurred into those functions? > return 0; > } > > @@ -971,11 +980,13 @@ static int check_slab(struct kmem_cache *s, struct page *page) > if (page->objects > maxobj) { > slab_err(s, page, "objects %u > max %u", > page->objects, maxobj); > + s->errors += 1; > return 0; > } > if (page->inuse > page->objects) { > slab_err(s, page, "inuse %u > max %u", > page->inuse, page->objects); > + s->errors += 1; > return 0; > } > /* Slab_pad_check fixes things up after itself */ > @@ -1008,8 +1019,10 @@ static int on_freelist(struct kmem_cache *s, struct page *page, void *search) > page->freelist = NULL; > page->inuse = page->objects; > slab_fix(s, "Freelist cleared"); > + s->errors += 1; > return 0; > } > + s->errors += 1; > break; > } > object = fp; > @@ -1026,12 +1039,14 @@ static int on_freelist(struct kmem_cache *s, struct page *page, void *search) > page->objects, max_objects); > page->objects = max_objects; > slab_fix(s, "Number of objects adjusted."); > + s->errors += 1; > } > if (page->inuse != page->objects - nr) { > slab_err(s, page, "Wrong object count. Counter is %d but counted were %d", > page->inuse, page->objects - nr); > page->inuse = page->objects - nr; > slab_fix(s, "Object count adjusted."); > + s->errors += 1; > } > return search == NULL; > } > @@ -4629,8 +4644,10 @@ static void validate_slab(struct kmem_cache *s, struct page *page) > u8 val = test_bit(__obj_to_index(s, addr, p), map) ? > SLUB_RED_INACTIVE : SLUB_RED_ACTIVE; > > - if (!check_object(s, page, p, val)) > + if (!check_object(s, page, p, val)) { > + s->errors += 1; > break; > + } > } > put_map(map); > unlock: > @@ -4650,9 +4667,11 @@ static int validate_slab_node(struct kmem_cache *s, > validate_slab(s, page); > count++; > } > - if (count != n->nr_partial) > + if (count != n->nr_partial) { > pr_err("SLUB %s: %ld partial slabs counted but counter=%ld\n", > s->name, count, n->nr_partial); > + s->errors += 1; > + } > > if (!(s->flags & SLAB_STORE_USER)) > goto out; > @@ -4661,20 +4680,23 @@ static int validate_slab_node(struct kmem_cache *s, > validate_slab(s, page); > count++; > } > - if (count != atomic_long_read(&n->nr_slabs)) > + if (count != atomic_long_read(&n->nr_slabs)) { > pr_err("SLUB: %s %ld slabs counted but counter=%ld\n", > s->name, count, atomic_long_read(&n->nr_slabs)); > + s->errors += 1; I think these here are a few cases where there's no slab_err() or slab_fix() call, and open coding setting errors is still required... > + } > > out: > spin_unlock_irqrestore(&n->list_lock, flags); > return count; > } > > -static long validate_slab_cache(struct kmem_cache *s) > +long validate_slab_cache(struct kmem_cache *s) > { > int node; > unsigned long count = 0; > struct kmem_cache_node *n; > + s->errors = 0; This would also go away if you use the kunit_resource design. I also think it's better if the test fully controls 'slab_errors', and it isn't reset by this function. > flush_all(s); > for_each_kmem_cache_node(s, node, n) > @@ -4682,6 +4704,8 @@ static long validate_slab_cache(struct kmem_cache *s) > > return count; > } > +EXPORT_SYMBOL(validate_slab_cache); > + > /* > * Generate lists of code addresses where slabcache objects are allocated > * and freed. > -- > 2.17.1