2015-09-12 1:47 GMT+03:00 Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>: > On Fri, 11 Sep 2015 10:02:29 +0800 Xishi Qiu <qiuxishi@xxxxxxxxxx> wrote: >> - if (likely(((addr + 7) & KASAN_SHADOW_MASK) >= 7)) >> + if (likely(IS_ALIGNED(addr, 8))) >> return false; > > Wouldn't IS_ALIGNED(addr, KASAN_SHADOW_SCALE_SIZE) be more appropriate? > > But I'm not really sure what the original code is trying to do. > Original code is trying to estimate whether we should check 2 shadow bytes or just 1 should be enough. > if ((addr + 7) & 7) >= 7) > > can only evaluate true if ((addr + 7) & 7) equals 7, so the ">=" could > be "==". > Yes, it could be "==". ">=" is just for consistency with similar code in memory_is_poisoned_2/4. If I'm not mistaken generic formula for such check looks like this: ((addr + size - 1) & KASAN_SHADOW_MASK) >= ((size - 1) & KASAN_SHADOW_MASK) But when size >= KASAN_SHADOW_SCALE_SIZE we could just check for alignment. > I think. The code looks a bit weird. A code comment would help. > > And how come memory_is_poisoned_16() does IS_ALIGNED(addr, 8)? Should > it be 16? > No, If 16 bytes are 8-byte aligned, then shadow is 2-bytes. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>