linux-kernel - Re: [PATCH 3/5] lib/bitmap: add test for bitmap_{from,to}

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Date:   Sat, 21 May 2022 00:38:05 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     linux-kernel@...r.kernel.org,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH 3/5] lib/bitmap: add test for bitmap_{from,to}_arr64

On Thu, May 19, 2022 at 08:09:29AM -0700, Guenter Roeck wrote:
> On Thu, Apr 28, 2022 at 01:51:14PM -0700, Yury Norov wrote:
> > Test newly added bitmap_{from,to}_arr64() functions similarly to
> > already existing bitmap_{from,to}_arr32() tests.
> > 
> > Signed-off-by: Yury Norov <yury.norov@...il.com>
> 
> With this patch in linux-next (including next-20220519), I see lots of
> bitmap test errors when booting 32-bit ppc images in qemu. Examples:
> 
> test_bitmap: [lib/test_bitmap.c:600] bitmaps contents differ: expected "0", got "0,65"
> ...
> test_bitmap: [lib/test_bitmap.c:600] bitmaps contents differ: expected "0,65", got "0,65,128"
> test_bitmap: [lib/test_bitmap.c:600] bitmaps contents differ: expected "0,65", got "0,65,128-129"
> test_bitmap: [lib/test_bitmap.c:600] bitmaps contents differ: expected "0,65", got "0,65,128-130"
> ...
> test_bitmap: [lib/test_bitmap.c:600] bitmaps contents differ: expected "0,65,128-143", got "0,65,128-143,208-209"
> test_bitmap: [lib/test_bitmap.c:600] bitmaps contents differ: expected "0,65,128-143", got "0,65,128-143,208-210"
> 
> and so on. It only  gets worse from there, and ends with:
> 
> test_bitmap: parselist: 14: input is '0-2047:128/256' OK, Time: 4274
> test_bitmap: bitmap_print_to_pagebuf: input is '0-32767
> ', Time: 127267
> test_bitmap: failed 337 out of 3801 tests
> 
> Other architectures and 64-bit ppc builds seem to be fine. 

So, the problem is in previous patch. I'll fold-in the following fix
into that if no objections.

diff --git a/lib/bitmap.c b/lib/bitmap.c
index 52b9912a71ea..97c14845f452 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -1585,7 +1585,7 @@ void bitmap_to_arr64(u64 *buf, const unsigned long *bitmap, unsigned int nbits)

        /* Clear tail bits in the last element of array beyond nbits. */
        if (nbits % 64)
-               buf[-1] &= GENMASK_ULL(nbits, 0);
+               buf[-1] &= GENMASK_ULL(nbits % 64, 0);
 }
 EXPORT_SYMBOL(bitmap_to_arr64);
 #endif