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Message-ID: <CAGS_qxpWtNLJ7_i5pDYhiGq_Jy+oPPc+HpWjNTJKAPyvQf+gsQ@mail.gmail.com>
Date: Thu, 1 Apr 2021 12:04:30 -0700
From: Daniel Latypov <dlatypov@...gle.com>
To: Marco Elver <elver@...gle.com>
Cc: glittao@...il.com, cl@...ux.com, penberg@...nel.org,
David Rientjes <rientjes@...gle.com>, iamjoonsoo.kim@....com,
akpm@...ux-foundation.org, vbabka@...e.cz,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
linux-mm@...ck.org, KUnit Development <kunit-dev@...glegroups.com>
Subject: Re: [PATCH v3 1/2] kunit: add a KUnit test for SLUB debugging functionality
On Thu, Apr 1, 2021 at 2:16 AM 'Marco Elver' via KUnit Development
<kunit-dev@...glegroups.com> wrote:
>
> [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@...glegroups.com if
> perhaps a KUnit dev should have another look, too.]
>
> On Wed, Mar 31, 2021 at 10:51AM +0200, glittao@...il.com wrote:
> > From: Oliver Glitta <glittao@...il.com>
> >
> > 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 <glittao@...il.com>
> > ---
> > 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).
The resource approach looks really good, but...
You'd be picking up a dependency on
https://lore.kernel.org/linux-kselftest/20210311152314.3814916-2-dlatypov@google.com/
current->kunit_test will always be NULL unless CONFIG_KASAN=y &&
CONFIG_KUNIT=y at the moment.
My patch drops the CONFIG_KASAN requirement and opens it up to all tests.
At the moment, it's just waiting another look over from Brendan or David.
Any ETA on that, folks? :)
So if you don't want to get blocked on that for now, I think it's fine to add:
#ifdef CONFIG_SLUB_KUNIT_TEST
int errors;
#endif
Side note: the resource example is really good, and maybe we should
steal it and add it near
https://www.kernel.org/doc/html/latest/dev-tools/kunit/tips.html#injecting-test-only-code
I had plans to update that section at some point after my patch landed
and added in `kunit_fail_current_test()`.
But this is an interesting inversion of that where we want the test to
only pass if that code gets executed.
>
> > };
> >
> > #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 <kunit/test.h>
> > +#include <linux/mm.h>
> > +#include <linux/slab.h>
> > +#include <linux/module.h>
> > +#include <linux/kernel.h>
> > +#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
>
> --
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