[PATCH] provide arch_test_bit_acquire for architectures that define test_bit

[Mikulas Patocka]

On Fri, 26 Aug 2022, Linus Torvalds wrote:

> On Fri, Aug 26, 2022 at 12:23 PM Geert Uytterhoeven
> <geert@xxxxxxxxxxxxxx> wrote:
> >
> >     include/asm-generic/bitops/non-instrumented-non-atomic.h:15:33:
> > error: implicit declaration of function 'arch_test_bit_acquire'; did
> > you mean '_test_bit_acquire'? [-Werror=implicit-function-declaration]
> >
> 
> Ahh. m68k isn't using any of the generic bitops headers.
> 
> *Most* architectures have that
> 
>    #include <asm-generic/bitops/non-atomic.h>
> 
> and get it that way, but while it's common, it's most definitely not universal:
> 
>   [torvalds@ryzen linux]$ git grep -L bitops/non-atomic.h
> arch/*/include/asm/bitops.h
>   arch/alpha/include/asm/bitops.h
>   arch/hexagon/include/asm/bitops.h
>   arch/ia64/include/asm/bitops.h
>   arch/m68k/include/asm/bitops.h
>   arch/s390/include/asm/bitops.h
>   arch/sparc/include/asm/bitops.h
>   arch/x86/include/asm/bitops.h
> 
> and of that list only x86 has the new arch_test_bit_acquire().
> 
> So I assume it's not just m68k, but also alpha, hexagon, ia64, s390
> and sparc that have this issue (unless they maybe have some other path
> that includes the gerneric ones, I didn't check).

For sparc, there is arch/sparc/include/asm/bitops_32.h and 
arch/sparc/include/asm/bitops_64.h that include 
asm-generic/bitops/non-atomic.h

For the others, the generic version is not included.

I'm wondering why do the architectures redefine test_bit, if their 
definition is equivalent to the generic one? We could just delete 
arch_test_bit and use "#define arch_test_bit generic_test_bit" as well.

> This was actually why my original suggested patch used the
> 'generic-non-atomic.h' header for it, because that is actually
> included regardless of any architecture headers directly from
> <linux/bitops.h>.
> 
> And it never triggered for me that Mikulas' updated patch then had
> this arch_test_bit_acquire() issue.
> 
> Something like the attached patch *MAY* fix it, but I really haven't
> thought about it a lot, and it's pretty ugly. Maybe it would be better
> to just add the
> 
>    #define arch_test_bit_acquire generic_test_bit_acquire
> 
> to the affected <asm/bitops.h> files instead, and then let those
> architectures decide on their own that maybe they want to use their
> own test_bit() function because it is _already_ an acquire one.
> 
> Mikulas?
> 
> Geert - any opinions on that "maybe the arch should just do that
> #define itself"? I don't think it actually matters for m68k, you end
> up with pretty much the same thing anyway, because
> "smp_load_acquire()" is just a load anyway..
> 
>                  Linus

Another untested patch ... tomorrow, I'll try to compile it, at least for 
architectures where Debian provides cross-compiling gcc.




From: Mikulas Patocka <mpatocka@xxxxxxxxxx>

Some architectures define their own arch_test_bit and they also need
arch_test_bit_acquire, otherwise they won't compile. We also clean up the
code by using the generic test_bit if that is equivalent to the
arch-specific version.

Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 8238b4579866 ("wait_on_bit: add an acquire memory barrier")

---
 arch/alpha/include/asm/bitops.h   |    7 ++-----
 arch/hexagon/include/asm/bitops.h |   15 +++++++++++++++
 arch/ia64/include/asm/bitops.h    |    7 ++-----
 arch/m68k/include/asm/bitops.h    |    7 ++-----
 arch/s390/include/asm/bitops.h    |   10 ++--------
 arch/sh/include/asm/bitops-op32.h |   12 ++----------
 6 files changed, 25 insertions(+), 33 deletions(-)

Index: linux-2.6/arch/alpha/include/asm/bitops.h
===================================================================
--- linux-2.6.orig/arch/alpha/include/asm/bitops.h
+++ linux-2.6/arch/alpha/include/asm/bitops.h
@@ -283,11 +283,8 @@ arch___test_and_change_bit(unsigned long
 	return (old & mask) != 0;
 }
 
-static __always_inline bool
-arch_test_bit(unsigned long nr, const volatile unsigned long *addr)
-{
-	return (1UL & (((const int *) addr)[nr >> 5] >> (nr & 31))) != 0UL;
-}
+#define arch_test_bit generic_test_bit
+#define arch_test_bit_acquire generic_test_bit_acquire
 
 /*
  * ffz = Find First Zero in word. Undefined if no zero exists,
Index: linux-2.6/arch/hexagon/include/asm/bitops.h
===================================================================
--- linux-2.6.orig/arch/hexagon/include/asm/bitops.h
+++ linux-2.6/arch/hexagon/include/asm/bitops.h
@@ -179,6 +179,21 @@ arch_test_bit(unsigned long nr, const vo
 	return retval;
 }
 
+static __always_inline bool
+arch_test_bit_acquire(unsigned long nr, const volatile unsigned long *addr)
+{
+	int retval;
+
+	asm volatile(
+	"{P0 = tstbit(%1,%2); if (P0.new) %0 = #1; if (!P0.new) %0 = #0;}\n"
+	: "=&r" (retval)
+	: "r" (addr[BIT_WORD(nr)]), "r" (nr % BITS_PER_LONG)
+	: "p0", "memory"
+	);
+
+	return retval;
+}
+
 /*
  * ffz - find first zero in word.
  * @word: The word to search
Index: linux-2.6/arch/ia64/include/asm/bitops.h
===================================================================
--- linux-2.6.orig/arch/ia64/include/asm/bitops.h
+++ linux-2.6/arch/ia64/include/asm/bitops.h
@@ -331,11 +331,8 @@ arch___test_and_change_bit(unsigned long
 	return (old & bit) != 0;
 }
 
-static __always_inline bool
-arch_test_bit(unsigned long nr, const volatile unsigned long *addr)
-{
-	return 1 & (((const volatile __u32 *) addr)[nr >> 5] >> (nr & 31));
-}
+#define arch_test_bit generic_test_bit
+#define arch_test_bit_acquire generic_test_bit_acquire
 
 /**
  * ffz - find the first zero bit in a long word
Index: linux-2.6/arch/s390/include/asm/bitops.h
===================================================================
--- linux-2.6.orig/arch/s390/include/asm/bitops.h
+++ linux-2.6/arch/s390/include/asm/bitops.h
@@ -176,14 +176,8 @@ arch___test_and_change_bit(unsigned long
 	return old & mask;
 }
 
-static __always_inline bool
-arch_test_bit(unsigned long nr, const volatile unsigned long *addr)
-{
-	const volatile unsigned long *p = __bitops_word(nr, addr);
-	unsigned long mask = __bitops_mask(nr);
-
-	return *p & mask;
-}
+#define arch_test_bit generic_test_bit
+#define arch_test_bit_acquire generic_test_bit_acquire
 
 static inline bool arch_test_and_set_bit_lock(unsigned long nr,
 					      volatile unsigned long *ptr)
Index: linux-2.6/arch/m68k/include/asm/bitops.h
===================================================================
--- linux-2.6.orig/arch/m68k/include/asm/bitops.h
+++ linux-2.6/arch/m68k/include/asm/bitops.h
@@ -157,11 +157,8 @@ arch___change_bit(unsigned long nr, vola
 	change_bit(nr, addr);
 }
 
-static __always_inline bool
-arch_test_bit(unsigned long nr, const volatile unsigned long *addr)
-{
-	return (addr[nr >> 5] & (1UL << (nr & 31))) != 0;
-}
+#define arch_test_bit generic_test_bit
+#define arch_test_bit_acquire generic_test_bit_acquire
 
 static inline int bset_reg_test_and_set_bit(int nr,
 					    volatile unsigned long *vaddr)
Index: linux-2.6/arch/sh/include/asm/bitops-op32.h
===================================================================
--- linux-2.6.orig/arch/sh/include/asm/bitops-op32.h
+++ linux-2.6/arch/sh/include/asm/bitops-op32.h
@@ -135,16 +135,8 @@ arch___test_and_change_bit(unsigned long
 	return (old & mask) != 0;
 }
 
-/**
- * arch_test_bit - Determine whether a bit is set
- * @nr: bit number to test
- * @addr: Address to start counting from
- */
-static __always_inline bool
-arch_test_bit(unsigned long nr, const volatile unsigned long *addr)
-{
-	return 1UL & (addr[BIT_WORD(nr)] >> (nr & (BITS_PER_LONG-1)));
-}
+#define arch_test_bit generic_test_bit
+#define arch_test_bit_acquire generic_test_bit_acquire
 
 #include <asm-generic/bitops/non-instrumented-non-atomic.h>