Re: [patch V5 01/32] mm/slab: Remove broken stack trace storage

Vlastimil Babka
2019-04-16T15:19:36Z

On 4/16/19 4:10 PM, Thomas Gleixner wrote:
> kstack_end() is broken on interrupt stacks as they are not guaranteed to be
> sized THREAD_SIZE and THREAD_SIZE aligned.
>
> As SLAB seems not to be used much with debugging enabled and might just go
> away completely according to:
>
> https://lkml.kernel.org/r/612f9b99-a75b-6aeb-cf92-7dc5421cd950@suse.cz
>
> just remove the bogus code instead of trying to fix it.
>
> Fixes: 98eb235b7feb ("[PATCH] page unmapping debug") - History tree
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Pekka Enberg <penberg@kernel.org>
> Cc: linux-mm@kvack.org

Acked-by: Vlastimil Babka <vbabka@suse.cz>

Thanks.

> ---
> V5: Remove the cruft.
> V4: Make it actually work
> V2: Made the code simpler to understand (Andy)
> ---
> mm/slab.c | 22 +++-------------------
> 1 file changed, 3 insertions(+), 19 deletions(-)
>
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -1470,33 +1470,17 @@ static bool is_debug_pagealloc_cache(str
> static void store_stackinfo(struct kmem_cache *cachep, unsigned long *addr,
> unsigned long caller)
> {
> - int size = cachep->object_size;
> + int size = cachep->object_size / sizeof(unsigned long);
>
> addr = (unsigned long *)&((char *)addr)[obj_offset(cachep)];
>
> - if (size < 5 * sizeof(unsigned long))
> + if (size < 4)
> return;
>
> *addr++ = 0x12345678;
> *addr++ = caller;
> *addr++ = smp_processor_id();
> - size -= 3 * sizeof(unsigned long);
> - {
> - unsigned long *sptr = &caller;
> - unsigned long svalue;
> -
> - while (!kstack_end(sptr)) {
> - svalue = *sptr++;
> - if (kernel_text_address(svalue)) {
> - *addr++ = svalue;
> - size -= sizeof(unsigned long);
> - if (size <= sizeof(unsigned long))
> - break;
> - }
> - }
> -
> - }
> - *addr++ = 0x87654321;
> + *addr = 0x87654321;
> }
>
> static void slab_kernel_map(struct kmem_cache *cachep, void *objp,
>