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lib/bitmap: drop optimization of bitmap_{from,to}_arr64 

bitmap_{from,to}_arr64() optimization is overly optimistic on 32-bit LE
architectures when it's wired to bitmap_copy_clear_tail().

bitmap_copy_clear_tail() takes care of unused bits in the bitmap up to
the next word boundary. But on 32-bit machines when copying bits from
bitmap to array of 64-bit words, it's expected that the unused part of
a recipient array must be cleared up to 64-bit boundary, so the last 4
bytes may stay untouched when nbits % 64 <= 32.

While the copying part of the optimization works correct, that clear-tail
trick makes corresponding tests reasonably fail:

test_bitmap: bitmap_to_arr64(nbits == 1): tail is not safely cleared: 0xa5a5a5a500000001 (must be 0x0000000000000001)

Fix it by removing bitmap_{from,to}_arr64() optimization for 32-bit LE
arches.

Reported-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/lkml/20230225184702.GA3587246@roeck-us.net/
Fixes: 0a97953fd2 ("lib: add bitmap_{from,to}_arr64")
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>
This commit is contained in:
Yury Norov 2023-02-27 11:24:36 -08:00
parent c4c14c2906
commit c1d2ba10f5
2 changed files with 4 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
include/linux/bitmap.h
View File

@ -302,12 +302,10 @@ void bitmap_to_arr32(u32 *buf, const unsigned long *bitmap,
#endif
/*
* On 64-bit systems bitmaps are represented as u64 arrays internally. On LE32
* machines the order of hi and lo parts of numbers match the bitmap structure.
* In both cases conversion is not needed when copying data from/to arrays of
* u64.
* On 64-bit systems bitmaps are represented as u64 arrays internally. So,
* the conversion is not needed when copying data from/to arrays of u64.
*/
#if (BITS_PER_LONG == 32) && defined(__BIG_ENDIAN)
#if BITS_PER_LONG == 32
void bitmap_from_arr64(unsigned long *bitmap, const u64 *buf, unsigned int nbits);
void bitmap_to_arr64(u64 *buf, const unsigned long *bitmap, unsigned int nbits);
#else

2
lib/bitmap.c
View File

@ -1495,7 +1495,7 @@ void bitmap_to_arr32(u32 *buf, const unsigned long *bitmap, unsigned int nbits)
EXPORT_SYMBOL(bitmap_to_arr32);
#endif
#if (BITS_PER_LONG == 32) && defined(__BIG_ENDIAN)
#if BITS_PER_LONG == 32
/**
* bitmap_from_arr64 - copy the contents of u64 array of bits to bitmap
* @bitmap: array of unsigned longs, the destination bitmap