From 7275b097851a5e2e0dd4da039c7e96b59ac5314e Mon Sep 17 00:00:00 2001 From: Rasmus Villemoes Date: Tue, 30 Oct 2018 15:04:59 -0700 Subject: linux/bitmap.h: handle constant zero-size bitmaps correctly The static inlines in bitmap.h do not handle a compile-time constant nbits==0 correctly (they dereference the passed src or dst pointers, despite only 0 words being valid to access). I had the 0-day buildbot chew on a patch [1] that would cause build failures for such cases without complaining, suggesting that we don't have any such users currently, at least for the 70 .config/arch combinations that was built. Should any turn up, make sure they use the out-of-line versions, which do handle nbits==0 correctly. This is of course not the most efficient, but it's much less churn than teaching all the static inlines an "if (zero_const_nbits())", and since we don't have any current instances, this doesn't affect existing code at all. [1] lkml.kernel.org/r/20180815085539.27485-1-linux@rasmusvillemoes.dk Link: http://lkml.kernel.org/r/20180818131623.8755-3-linux@rasmusvillemoes.dk Signed-off-by: Rasmus Villemoes Reviewed-by: Andy Shevchenko Cc: Yury Norov Cc: Rasmus Villemoes Cc: Sudeep Holla Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/bitmap.h | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) (limited to 'include/linux/bitmap.h') diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h index acf5e8df3504..a9805bacbd7c 100644 --- a/include/linux/bitmap.h +++ b/include/linux/bitmap.h @@ -204,8 +204,13 @@ extern int bitmap_print_to_pagebuf(bool list, char *buf, #define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) & (BITS_PER_LONG - 1))) #define BITMAP_LAST_WORD_MASK(nbits) (~0UL >> (-(nbits) & (BITS_PER_LONG - 1))) +/* + * The static inlines below do not handle constant nbits==0 correctly, + * so make such users (should any ever turn up) call the out-of-line + * versions. + */ #define small_const_nbits(nbits) \ - (__builtin_constant_p(nbits) && (nbits) <= BITS_PER_LONG) + (__builtin_constant_p(nbits) && (nbits) <= BITS_PER_LONG && (nbits) > 0) static inline void bitmap_zero(unsigned long *dst, unsigned int nbits) { -- cgit v1.2.3 From c8cebc553368209426f7279736db4f88f1853396 Mon Sep 17 00:00:00 2001 From: Rasmus Villemoes Date: Tue, 30 Oct 2018 15:05:02 -0700 Subject: linux/bitmap.h: remove redundant uses of small_const_nbits() In the _zero, _fill and _copy functions, the small_const_nbits branch is redundant. If nbits is small and const, gcc knows full well that BITS_TO_LONGS(nbits) is 1, so len is also a compile-time constant (sizeof(long)), and calling memset or memcpy with a length argument of sizeof(long) makes gcc generate the expected code anyway: #include void a(unsigned long *x) { memset(x, 0, 8); } void b(unsigned long *x) { memset(x, 0xff, 8); } void c(unsigned long *x, const unsigned long *y) { memcpy(x, y, 8); } turns into 0000000000000000 : 0: 48 c7 07 00 00 00 00 movq $0x0,(%rdi) 7: c3 retq 8: 0f 1f 84 00 00 00 00 nopl 0x0(%rax,%rax,1) f: 00 0000000000000010 : 10: 48 c7 07 ff ff ff ff movq $0xffffffffffffffff,(%rdi) 17: c3 retq 18: 0f 1f 84 00 00 00 00 nopl 0x0(%rax,%rax,1) 1f: 00 0000000000000020 : 20: 48 8b 06 mov (%rsi),%rax 23: 48 89 07 mov %rax,(%rdi) 26: c3 retq Link: http://lkml.kernel.org/r/20180818131623.8755-4-linux@rasmusvillemoes.dk Signed-off-by: Rasmus Villemoes Reviewed-by: Andy Shevchenko Cc: Yury Norov Cc: Rasmus Villemoes Cc: Sudeep Holla Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/bitmap.h | 24 ++++++------------------ 1 file changed, 6 insertions(+), 18 deletions(-) (limited to 'include/linux/bitmap.h') diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h index a9805bacbd7c..004cd42a3c4d 100644 --- a/include/linux/bitmap.h +++ b/include/linux/bitmap.h @@ -214,33 +214,21 @@ extern int bitmap_print_to_pagebuf(bool list, char *buf, static inline void bitmap_zero(unsigned long *dst, unsigned int nbits) { - if (small_const_nbits(nbits)) - *dst = 0UL; - else { - unsigned int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long); - memset(dst, 0, len); - } + unsigned int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long); + memset(dst, 0, len); } static inline void bitmap_fill(unsigned long *dst, unsigned int nbits) { - if (small_const_nbits(nbits)) - *dst = ~0UL; - else { - unsigned int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long); - memset(dst, 0xff, len); - } + unsigned int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long); + memset(dst, 0xff, len); } static inline void bitmap_copy(unsigned long *dst, const unsigned long *src, unsigned int nbits) { - if (small_const_nbits(nbits)) - *dst = *src; - else { - unsigned int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long); - memcpy(dst, src, len); - } + unsigned int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long); + memcpy(dst, src, len); } /* -- cgit v1.2.3 From d9873969fa8725dc6a5a21ab788c057fd8719751 Mon Sep 17 00:00:00 2001 From: Rasmus Villemoes Date: Tue, 30 Oct 2018 15:05:07 -0700 Subject: linux/bitmap.h: fix type of nbits in bitmap_shift_right() Most other bitmap API, including the OOL version __bitmap_shift_right, take unsigned nbits. This was accidentally left out from 2fbad29917c98. Link: http://lkml.kernel.org/r/20180818131623.8755-5-linux@rasmusvillemoes.dk Fixes: 2fbad29917c98 ("lib: bitmap: change bitmap_shift_right to take unsigned parameters") Signed-off-by: Rasmus Villemoes Reported-by: Yury Norov Reviewed-by: Andy Shevchenko Cc: Rasmus Villemoes Cc: Sudeep Holla Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/bitmap.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include/linux/bitmap.h') diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h index 004cd42a3c4d..4032680e629d 100644 --- a/include/linux/bitmap.h +++ b/include/linux/bitmap.h @@ -391,7 +391,7 @@ static __always_inline void bitmap_clear(unsigned long *map, unsigned int start, } static inline void bitmap_shift_right(unsigned long *dst, const unsigned long *src, - unsigned int shift, int nbits) + unsigned int shift, unsigned int nbits) { if (small_const_nbits(nbits)) *dst = (*src & BITMAP_LAST_WORD_MASK(nbits)) >> shift; -- cgit v1.2.3 From 41e7b1661ffbf562d3aa2b7ce4ad283db50b711a Mon Sep 17 00:00:00 2001 From: Rasmus Villemoes Date: Tue, 30 Oct 2018 15:05:10 -0700 Subject: linux/bitmap.h: relax comment on compile-time constant nbits It's not clear what's so horrible about emitting a function call to handle a run-time sized bitmap. Moreover, gcc also emits a function call for a compile-time-constant-but-huge nbits, so the comment isn't even accurate. Link: http://lkml.kernel.org/r/20180818131623.8755-6-linux@rasmusvillemoes.dk Signed-off-by: Rasmus Villemoes Reviewed-by: Andy Shevchenko Cc: Yury Norov Cc: Rasmus Villemoes Cc: Sudeep Holla Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/bitmap.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'include/linux/bitmap.h') diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h index 4032680e629d..f58e97446abc 100644 --- a/include/linux/bitmap.h +++ b/include/linux/bitmap.h @@ -28,8 +28,8 @@ * The available bitmap operations and their rough meaning in the * case that the bitmap is a single unsigned long are thus: * - * Note that nbits should be always a compile time evaluable constant. - * Otherwise many inlines will generate horrible code. + * The generated code is more efficient when nbits is known at + * compile-time and at most BITS_PER_LONG. * * :: * -- cgit v1.2.3