On 2/5/25 01:44, Hyesoo Yu wrote:
> Previously, the restore occured after printing the object in slub.
> After commit 47d911b02cbe ("slab: make check_object() more consistent"),
> the bytes are printed after the restore. This information about the bytes
> before the restore is highly valuable for debugging purpose.
> For instance, in a event of cache issue, it displays byte patterns
> by breaking them down into 64-bytes units. Without this information,
> we can only speculate on how it was broken. Hence the corrupted regions
> should be printed prior to the restoration process. However if an object breaks
> in multiple places, the same log may be output multiple times.
> Therefore the slub log is reported only once to prevent redundant printing,
> by sending a parameter indicating whether an error has occurred previously.
>
> Changes in v2:
> - Instead of using print_section every time on check_bytes_and_report,
> just print it once for the entire slub object before the restore.
>
> Signed-off-by: Hyesoo Yu <hyesoo.yu@xxxxxxxxxxx>
> ---
> mm/slub.c | 25 ++++++++++++-------------
> 1 file changed, 12 insertions(+), 13 deletions(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index ea956cb4b8be..7a9f7a2c17d7 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1182,7 +1182,7 @@ static void restore_bytes(struct kmem_cache *s, char *message, u8 data,
> static pad_check_attributes int
> check_bytes_and_report(struct kmem_cache *s, struct slab *slab,
> u8 *object, char *what,
> - u8 *start, unsigned int value, unsigned int bytes)
> + u8 *start, unsigned int value, unsigned int bytes, int slab_obj_print)
It would be better to redistribute the arguments among lines to fit each <80
chars. The previous line is underutilized. Also could the new argument be bool?
> {
> u8 *fault;
> u8 *end;
> @@ -1205,6 +1205,10 @@ check_bytes_and_report(struct kmem_cache *s, struct slab *slab,
> 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);
Hm we have slab_bug() above this, not slab_err(). So this is another place
that would need to take care a WARN is called with your other patch.
> + if (slab_obj_print) {
> + print_trailer(s, slab, object);
> + add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
I guess we could do the WARN here. If panic_on_warn is enabled it will not
report all problems that check_object() could find and panic on the first
one. But that would have happened too with your slab_fix() approach
(slab_fix() called from restore_bytes() below). I think we can live with
that instead of needing two separate reporting and fixing rounds from
check_object().
Could you send the two patches as a series in v3, as they are
inter-dependent? Thanks.
> + }
>
> skip_bug_print:
> restore_bytes(s, what, value, fault, end);
> @@ -1268,7 +1272,7 @@ static int check_pad_bytes(struct kmem_cache *s, struct slab *slab, u8 *p)
> return 1;
>
> return check_bytes_and_report(s, slab, p, "Object padding",
> - p + off, POISON_INUSE, size_from_object(s) - off);
> + p + off, POISON_INUSE, size_from_object(s) - off, 1);
> }
>
> /* Check the pad bytes at the end of a slab page */
> @@ -1318,11 +1322,11 @@ static int check_object(struct kmem_cache *s, struct slab *slab,
>
> if (s->flags & SLAB_RED_ZONE) {
> if (!check_bytes_and_report(s, slab, object, "Left Redzone",
> - object - s->red_left_pad, val, s->red_left_pad))
> + object - s->red_left_pad, val, s->red_left_pad, ret))
> ret = 0;
>
> if (!check_bytes_and_report(s, slab, object, "Right Redzone",
> - endobject, val, s->inuse - s->object_size))
> + endobject, val, s->inuse - s->object_size, ret))
> ret = 0;
>
> if (slub_debug_orig_size(s) && val == SLUB_RED_ACTIVE) {
> @@ -1331,7 +1335,7 @@ static int check_object(struct kmem_cache *s, struct slab *slab,
> if (s->object_size > orig_size &&
> !check_bytes_and_report(s, slab, object,
> "kmalloc Redzone", p + orig_size,
> - val, s->object_size - orig_size)) {
> + val, s->object_size - orig_size, ret)) {
> ret = 0;
> }
> }
> @@ -1339,7 +1343,7 @@ static int check_object(struct kmem_cache *s, struct slab *slab,
> if ((s->flags & SLAB_POISON) && s->object_size < s->inuse) {
> if (!check_bytes_and_report(s, slab, p, "Alignment padding",
> endobject, POISON_INUSE,
> - s->inuse - s->object_size))
> + s->inuse - s->object_size, ret))
> ret = 0;
> }
> }
> @@ -1355,11 +1359,11 @@ static int check_object(struct kmem_cache *s, struct slab *slab,
> if (kasan_meta_size < s->object_size - 1 &&
> !check_bytes_and_report(s, slab, p, "Poison",
> p + kasan_meta_size, POISON_FREE,
> - s->object_size - kasan_meta_size - 1))
> + s->object_size - kasan_meta_size - 1, ret))
> ret = 0;
> if (kasan_meta_size < s->object_size &&
> !check_bytes_and_report(s, slab, p, "End Poison",
> - p + s->object_size - 1, POISON_END, 1))
> + p + s->object_size - 1, POISON_END, 1, ret))
> ret = 0;
> }
> /*
> @@ -1385,11 +1389,6 @@ static int check_object(struct kmem_cache *s, struct slab *slab,
> ret = 0;
> }
>
> - if (!ret && !slab_in_kunit_test()) {
> - print_trailer(s, slab, object);
> - add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
> - }
> -
> return ret;
> }
>
