Re: [PATCH v4 2/3] mm/slub, kunit: add a KUnit test for SLUB debugging functionality

From: Oliver Glitta
Date: Thu Apr 15 2021 - 06:12:04 EST

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In reply to: Daniel Latypov: "Re: [PATCH v4 2/3] mm/slub, kunit: add a KUnit test for SLUB debugging functionality"
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ut 13. 4. 2021 o 23:33 Daniel Latypov <dlatypov@xxxxxxxxxx> napísal(a):
>
> On Tue, Apr 13, 2021 at 3:07 AM <glittao@xxxxxxxxx> wrote:
> >
> > From: Oliver Glitta <glittao@xxxxxxxxx>
> >
> > 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.
> > Because the test deliberatly modifies non-allocated objects, it depends on
>
> nit: *deliberately
>
> > !KASAN which would have otherwise prevented that.
> >
> > Use kunit_resource to count errors in cache and silence bug reports.
> > Count error whenever slab_bug() or slab_fix() is called or when
> > the count of pages is wrong.
> >
> > Signed-off-by: Oliver Glitta <glittao@xxxxxxxxx>
>
> Acked-by: Daniel Latypov <dlatypov@xxxxxxxxxx>
>

Thank you.

> Looks good to me!
> My one minor suggestion: perhaps let's log a summary of the error or
> the func name in slab_add_kunit_errors().
>

That is a good suggestion, but now we want to know if this version is stable.
We will take a look at that in the follow-up patch.

> > ---
> > Changes since v3
> >
> > Use kunit_resource to silence bug reports and count errors suggested by
> > Marco Elver.
> > Make the test depends on !KASAN thanks to report from the kernel test robot.
> >
> > 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.
> > lib/Kconfig.debug | 12 ++++
> > lib/Makefile | 1 +
> > lib/slub_kunit.c | 150 ++++++++++++++++++++++++++++++++++++++++++++++
> > mm/slab.h | 1 +
> > mm/slub.c | 50 ++++++++++++++--
> > 5 files changed, 209 insertions(+), 5 deletions(-)
> > create mode 100644 lib/slub_kunit.c
> >
> > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> > index 2779c29d9981..9b8a0d754278 100644
> > --- a/lib/Kconfig.debug
> > +++ b/lib/Kconfig.debug
> > @@ -2371,6 +2371,18 @@ 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 && !KASAN
> > + default KUNIT_ALL_TESTS
> > + help
> > + This builds SLUB allocator unit test.
> > + Tests SLUB cache debugging functionality.
> > + For more information on KUnit and unit tests in general please refer
> > + to the KUnit documentation in Documentation/dev-tools/kunit/.
> > +
> > + If unsure, say N.
> > +
> > config TEST_UDELAY
> > tristate "udelay test driver"
> > help
> > diff --git a/lib/Makefile b/lib/Makefile
> > index b5307d3eec1a..1e59c6714ed8 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-$(CONFIG_SLUB_KUNIT_TEST) += slub_kunit.o
> >
> > obj-$(CONFIG_GENERIC_LIB_DEVMEM_IS_ALLOWED) += devmem_is_allowed.o
> > diff --git a/lib/slub_kunit.c b/lib/slub_kunit.c
> > new file mode 100644
> > index 000000000000..cb9ae9f7e8a6
> > --- /dev/null
> > +++ b/lib/slub_kunit.c
> > @@ -0,0 +1,150 @@
> > +// 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 struct kunit_resource resource;
> > +static int slab_errors;
> > +
> > +static void test_clobber_zone(struct kunit *test)
> > +{
> > + struct kmem_cache *s = kmem_cache_create("TestSlub_RZ_alloc", 64, 0,
> > + SLAB_RED_ZONE, NULL);
> > + u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
> > +
> > + p[64] = 0x12;
> > +
> > + validate_slab_cache(s);
> > + KUNIT_EXPECT_EQ(test, 2, slab_errors);
> > +
> > + kmem_cache_free(s, p);
> > + kmem_cache_destroy(s);
>
> Might not be worth doing for now:
> I see kmem_cache_destroy() has a `if (err) { pr_err(...); dump_stack(); }` call.
> Does it make sense to cause that to fail the test?
>
> I see it's defined in mm/slab_common.c, so we might not want to touch
> that in this patch.
>
> > +}
> > +
> > +static void test_next_pointer(struct kunit *test)
> > +{
> > + struct kmem_cache *s = kmem_cache_create("TestSlub_next_ptr_free", 64, 0,
> > + SLAB_POISON, 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;
> > +
>
> I really like this test!
> I think it'll be a good example to point to wrt handle mutating state
> in tests (clear comments, using whitespace to break up steps, setting
> up clear EXPECT calls, etc.)
>
> > + /*
> > + * Expecting three errors.
> > + * One for the corrupted freechain and the other one for the wrong
> > + * count of objects in use. The third error is fixing broken cache.
> > + */
> > + validate_slab_cache(s);
> > + KUNIT_EXPECT_EQ(test, 3, slab_errors);
> > +
> > + /*
> > + * Try to repair corrupted freepointer.
> > + * Still expecting two errors. The first for the wrong count
> > + * of objects in use.
> > + * The second error is for fixing broken cache.
> > + */
> > + *ptr_addr = tmp;
> > + slab_errors = 0;
> > +
> > + validate_slab_cache(s);
> > + KUNIT_EXPECT_EQ(test, 2, slab_errors);
> > +
> > + /*
> > + * Previous validation repaired the count of objects in use.
> > + * Now expecting no error.
> > + */
> > + slab_errors = 0;
> > + validate_slab_cache(s);
> > + KUNIT_EXPECT_EQ(test, 0, slab_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, NULL);
> > + u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
> > +
> > + kmem_cache_free(s, p);
> > + *p = 0x78;
> > +
> > + validate_slab_cache(s);
> > + KUNIT_EXPECT_EQ(test, 2, slab_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, 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, 2, slab_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, 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, 2, slab_errors);
> > + kmem_cache_destroy(s);
> > +}
> > +
> > +static int test_init(struct kunit *test)
> > +{
> > + slab_errors = 0;
> > +
> > + /* FIXME: remove when CONFIG_KASAN requirement is dropped. */
> > + current->kunit_test = test;
> > +
> > + kunit_add_named_resource(test, NULL, NULL, &resource,
> > + "slab_errors", &slab_errors);
> > + return 0;
> > +}
> > +
> > +static void test_exit(struct kunit *test)
> > +{
> > + /* FIXME: remove when CONFIG_KASAN requirement is dropped. */
> > + current->kunit_test = NULL;
> > +}
> > +
> > +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",
> > + .init = test_init,
> > + .exit = test_exit,
> > + .test_cases = test_cases,
> > +};
> > +kunit_test_suite(test_suite);
> > +
> > +MODULE_LICENSE("GPL");
> > diff --git a/mm/slab.h b/mm/slab.h
> > index 076582f58f68..95cf42eb8396 100644
> > --- a/mm/slab.h
> > +++ b/mm/slab.h
> > @@ -215,6 +215,7 @@ 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/slub.c b/mm/slub.c
> > index 3021ce9bf1b3..d7df8841d90a 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -35,6 +35,7 @@
> > #include <linux/prefetch.h>
> > #include <linux/memcontrol.h>
> > #include <linux/random.h>
> > +#include <kunit/test.h>
> >
> > #include <trace/events/kmem.h>
> >
> > @@ -447,6 +448,26 @@ static inline bool cmpxchg_double_slab(struct kmem_cache *s, struct page *page,
> > static unsigned long object_map[BITS_TO_LONGS(MAX_OBJS_PER_PAGE)];
> > static DEFINE_SPINLOCK(object_map_lock);
> >
> > +#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);
> > + return true;
> > +}
> > +#else
> > +static inline bool slab_add_kunit_errors(void) { return false; }
> > +#endif
> > +
> > /*
> > * Determine a map of object in use on a page.
> > *
> > @@ -676,6 +697,9 @@ static void slab_fix(struct kmem_cache *s, char *fmt, ...)
> > struct va_format vaf;
> > va_list args;
> >
> > + if (slab_add_kunit_errors())
> > + return;
> > +
> > va_start(args, fmt);
> > vaf.fmt = fmt;
> > vaf.va = &args;
> > @@ -739,6 +763,9 @@ 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)
> > {
> > + if (slab_add_kunit_errors())
> > + return;
> > +
> > slab_bug(s, "%s", reason);
>
> Would it be a good idea for us to log the error text in slab_add_kunit_errors()?
> Otherwise we could end up with getting the same error count but from
> an unexpected set of code paths.
>
> Boils down to using this macro
> kunit_info(current->kunit_test, "%s", reason);
>
> Perhaps we could get away with just duplicating (a subset of) what
> we'd pass into slab_bug(), i.e.
> if (slab_add_kunit_errors("%s", reason)) return;
> if (slab_add_kunit_errors("%s overwritten", what) return;
> If the string we're printing is too annoying to duplicate, can get
> away with just using __func__ as well.
>
> Or a more messy alternative would be to add some #if'd code in
> slab_bug(), but I don't know if that's as good of an idea.
>
> > print_trailer(s, page, object);
> > }
> > @@ -749,6 +776,9 @@ static __printf(3, 4) void slab_err(struct kmem_cache *s, struct page *page,
> > va_list args;
> > char buf[100];
> >
> > + if (slab_add_kunit_errors())
> > + return;
> > +
> > va_start(args, fmt);
> > vsnprintf(buf, sizeof(buf), fmt, args);
> > va_end(args);
> > @@ -798,12 +828,16 @@ static int check_bytes_and_report(struct kmem_cache *s, struct page *page,
> > while (end > fault && end[-1] == value)
> > end--;
> >
> > + if (slab_add_kunit_errors())
> > + goto skip_bug_print;
> > +
> > 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);
> > + fault, end - 1, fault - addr,
> > + fault[0], value);
> > print_trailer(s, page, object);
> >
> > +skip_bug_print:
> > restore_bytes(s, what, value, fault, end);
> > return 0;
> > }
> > @@ -4650,9 +4684,11 @@ 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);
> > + slab_add_kunit_errors();
> > + }
> >
> > if (!(s->flags & SLAB_STORE_USER))
> > goto out;
> > @@ -4661,16 +4697,18 @@ 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));
> > + slab_add_kunit_errors();
> > + }
> >
> > 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;
> > @@ -4682,6 +4720,8 @@ 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.
> > --
> > 2.31.1.272.g89b43f80a5
> >

Next message: Christophe Leroy: "Re: linux-next: manual merge of the akpm-current tree with the powerpc tree"
Previous message: Alexandre Torgue: "[PATCH 11/13] ARM: dts: stm32: fix LTDC port node on STM32 MCU ad MPU"
In reply to: Daniel Latypov: "Re: [PATCH v4 2/3] mm/slub, kunit: add a KUnit test for SLUB debugging functionality"
Next in thread: Vlastimil Babka: "Re: [PATCH v4 2/3] mm/slub, kunit: add a KUnit test for SLUB debugging functionality"
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