On 6/16/21 6:25 PM, Georgi Djakov wrote:
> When running the kernel with panic_on_taint, the usual slub debug error
> messages are not being printed when object corruption happens. That's
> because we panic in add_taint(), which is called before printing the
> additional information. This is a bit unfortunate as the error messages
> are actually very useful, especially before a panic. Let's fix this by
> moving add_taint() after the errors are printed on the console.
>
> Signed-off-by: Georgi Djakov <quic_c_gdjako@xxxxxxxxxxx>
Makes sense.
While at it, I wonder if we should use LOCKDEP_STILL_OK instead of
LOCKDEP_NOW_UNRELIABLE. Isn't it too pessimistic to assume that some slab's
memory corruption hit some lock state?
> ---
> mm/slub.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index a8b0daa1a307..ce7b8e4551b5 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -719,8 +719,6 @@ static void slab_bug(struct kmem_cache *s, char *fmt, ...)
> pr_err("=============================================================================\n");
> pr_err("BUG %s (%s): %pV\n", s->name, print_tainted(), &vaf);
> pr_err("-----------------------------------------------------------------------------\n\n");
> -
> - add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
> va_end(args);
> }
>
> @@ -801,6 +799,7 @@ void object_err(struct kmem_cache *s, struct page *page,
>
> slab_bug(s, "%s", reason);
> print_trailer(s, page, object);
> + add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
> }
>
> static __printf(3, 4) void slab_err(struct kmem_cache *s, struct page *page,
> @@ -818,6 +817,7 @@ static __printf(3, 4) void slab_err(struct kmem_cache *s, struct page *page,
> slab_bug(s, "%s", buf);
> print_page_info(page);
> dump_stack();
> + add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
> }
>
> static void init_object(struct kmem_cache *s, void *object, u8 val)
> @@ -869,6 +869,7 @@ static int check_bytes_and_report(struct kmem_cache *s, struct page *page,
> fault, end - 1, fault - addr,
> fault[0], value);
> print_trailer(s, page, object);
> + add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
>
> skip_bug_print:
> restore_bytes(s, what, value, fault, end);
>
