Re: [PATCH v5 2/3] mm/slub, kunit: add a KUnit test for SLUB debugging functionality

[Oliver Glitta <glittao@xxxxxxxxx>]

ut 11. 5. 2021 o 17:16 Marco Elver <elver@xxxxxxxxxx> napísal(a):

>
> On Tue, 11 May 2021 at 17:07, <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.
> > Tests next_pointer, first_word and clobber_50th_byte do not run
> > with KASAN option on. Because the test deliberately modifies non-allocated
> > objects.
> >
> > 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>
>
> I think I had already reviewed v4, and the changes here are fine:
>
> Reviewed-by: Marco Elver <elver@xxxxxxxxxx>

Thank you again.

I’m sorry about, I forgot to add this tags. 

> Others who had reviewed/acked v4, probably need to re-ack/review.
> Note, I think if you addressed the comments and didn't change much
> else, you can typically carry the acks/reviews, unless the other
> person changed their mind explicitly.

>

> > ---

> > Changes since v4
> > Use two tests with KASAN dependency.
> > Remove setting current test during init and exit.
> >
> > 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  | 155 ++++++++++++++++++++++++++++++++++++++++++++++
> >  mm/slab.h         |   1 +
> >  mm/slub.c         |  46 +++++++++++++-
> >  5 files changed, 212 insertions(+), 3 deletions(-)
> >  create mode 100644 lib/slub_kunit.c
> >
> > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> > index 678c13967580..7723f58a9394 100644
> > --- a/lib/Kconfig.debug
> > +++ b/lib/Kconfig.debug
> > @@ -2429,6 +2429,18 @@ 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
> > +       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 e11cfc18b6c0..386215dcb0a0 100644
> > --- a/lib/Makefile
> > +++ b/lib/Makefile
> > @@ -353,5 +353,6 @@ 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..f28965f64ef6
> > --- /dev/null
> > +++ b/lib/slub_kunit.c
> > @@ -0,0 +1,155 @@
> > +// 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);
> > +
> > +       kasan_disable_current();
> > +       p[64] = 0x12;
> > +
> > +       validate_slab_cache(s);
> > +       KUNIT_EXPECT_EQ(test, 2, slab_errors);
> > +
> > +       kasan_enable_current();
> > +       kmem_cache_free(s, p);
> > +       kmem_cache_destroy(s);
> > +}
> > +
> > +#ifndef CONFIG_KASAN
> > +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;
> > +
> > +       /*
> > +        * 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);
> > +}
> > +#endif
> > +
> > +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);
> > +
> > +       kasan_disable_current();
> > +       kmem_cache_free(s, p);
> > +       p[64] = 0xab;
> > +
> > +       validate_slab_cache(s);
> > +       KUNIT_EXPECT_EQ(test, 2, slab_errors);
> > +
> > +       kasan_enable_current();
> > +       kmem_cache_destroy(s);
> > +}
> > +
> > +static int test_init(struct kunit *test)
> > +{
> > +       slab_errors = 0;
> > +
> > +       kunit_add_named_resource(test, NULL, NULL, &resource,
> > +                                       "slab_errors", &slab_errors);
> > +       return 0;
> > +}
> > +
> > +static void test_exit(struct kunit *test) {}
>
> Does removing test_exit() and not setting it below work?

Yes this works. Thank you for that. I try to remove function but I didn't think about not setting it, so it didn't work. I will fix it. 

> > +static struct kunit_case test_cases[] = {
> > +       KUNIT_CASE(test_clobber_zone),
> > +
> > +#ifndef CONFIG_KASAN
> > +       KUNIT_CASE(test_next_pointer),
> > +       KUNIT_CASE(test_first_word),
> > +       KUNIT_CASE(test_clobber_50th_byte),
> > +#endif
> > +
> > +       KUNIT_CASE(test_clobber_redzone_free),
> > +       {}
>
> This is better, and tells us which tests exactly were the ones causing
> problems with KASAN.
>
>
> > +};
> > +
> > +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 18c1927cd196..9b690fa44cae 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 feda53ae62ba..985fd6ef033c 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.
> >   *
> > @@ -677,6 +698,9 @@ 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;
> > @@ -740,6 +764,9 @@ 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);
> >         print_trailer(s, page, object);
> >  }
> > @@ -750,6 +777,9 @@ 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);
> > @@ -799,12 +829,16 @@ 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("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);
> >
> > +skip_bug_print:
> >         restore_bytes(s, what, value, fault, end);
> >         return 0;
> >  }
> > @@ -4662,9 +4696,11 @@ 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;
> > @@ -4673,16 +4709,18 @@ 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;
> > @@ -4694,6 +4732,8 @@ 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
> >