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Date:   Fri, 31 May 2019 17:01:21 +0100
From:   Mark Rutland <mark.rutland@arm.com>
To:     Marco Elver <elver@google.com>
Cc:     peterz@infradead.org, aryabinin@virtuozzo.com, dvyukov@google.com,
        glider@google.com, andreyknvl@google.com, hpa@zytor.com,
        corbet@lwn.net, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
        x86@kernel.org, arnd@arndb.de, jpoimboe@redhat.com,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arch@vger.kernel.org, kasan-dev@googlegroups.com
Subject: Re: [PATCH v3 3/3] asm-generic, x86: Add bitops instrumentation for
 KASAN
Message-ID: <20190531160120.GB2646@lakrids.cambridge.arm.com>
References: <20190531150828.157832-1-elver@google.com>
 <20190531150828.157832-4-elver@google.com>
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On Fri, May 31, 2019 at 05:08:31PM +0200, Marco Elver wrote:
> This adds a new header to asm-generic to allow optionally instrumenting
> architecture-specific asm implementations of bitops.
> 
> This change includes the required change for x86 as reference and
> changes the kernel API doc to point to bitops-instrumented.h instead.
> Rationale: the functions in x86's bitops.h are no longer the kernel API
> functions, but instead the arch_ prefixed functions, which are then
> instrumented via bitops-instrumented.h.
> 
> Other architectures can similarly add support for asm implementations of
> bitops.
> 
> The documentation text was derived from x86 and existing bitops
> asm-generic versions: 1) references to x86 have been removed; 2) as a
> result, some of the text had to be reworded for clarity and consistency.
> 
> Tested: using lib/test_kasan with bitops tests (pre-requisite patch).
> 
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=198439
> Signed-off-by: Marco Elver <elver@google.com>
> ---
> Changes in v3:
> * Remove references to 'x86' in API documentation; as a result, had to
>   reword doc text for clarify and consistency.
> * Remove #ifdef, since it is assumed that if asm-generic bitops
>   implementations are used, bitops-instrumented.h is not needed.

Thanks for sorting this out. FWIW:

Acked-by: Mark Rutland <mark.rutland@arm.com>

Mark.

> 
> Changes in v2:
> * Instrument word-sized accesses, as specified by the interface.
> ---
>  Documentation/core-api/kernel-api.rst     |   2 +-
>  arch/x86/include/asm/bitops.h             | 189 ++++------------
>  include/asm-generic/bitops-instrumented.h | 263 ++++++++++++++++++++++
>  3 files changed, 302 insertions(+), 152 deletions(-)
>  create mode 100644 include/asm-generic/bitops-instrumented.h
> 
> diff --git a/Documentation/core-api/kernel-api.rst b/Documentation/core-api/kernel-api.rst
> index a29c99d13331..65266fa1b706 100644
> --- a/Documentation/core-api/kernel-api.rst
> +++ b/Documentation/core-api/kernel-api.rst
> @@ -51,7 +51,7 @@ The Linux kernel provides more basic utility functions.
>  Bit Operations
>  --------------
>  
> -.. kernel-doc:: arch/x86/include/asm/bitops.h
> +.. kernel-doc:: include/asm-generic/bitops-instrumented.h
>     :internal:
>  
>  Bitmap Operations
> diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
> index 8e790ec219a5..ba15d53c1ca7 100644
> --- a/arch/x86/include/asm/bitops.h
> +++ b/arch/x86/include/asm/bitops.h
> @@ -49,23 +49,8 @@
>  #define CONST_MASK_ADDR(nr, addr)	WBYTE_ADDR((void *)(addr) + ((nr)>>3))
>  #define CONST_MASK(nr)			(1 << ((nr) & 7))
>  
> -/**
> - * set_bit - Atomically set a bit in memory
> - * @nr: the bit to set
> - * @addr: the address to start counting from
> - *
> - * This function is atomic and may not be reordered.  See __set_bit()
> - * if you do not require the atomic guarantees.
> - *
> - * Note: there are no guarantees that this function will not be reordered
> - * on non x86 architectures, so if you are writing portable code,
> - * make sure not to rely on its reordering guarantees.
> - *
> - * Note that @nr may be almost arbitrarily large; this function is not
> - * restricted to acting on a single-word quantity.
> - */
>  static __always_inline void
> -set_bit(long nr, volatile unsigned long *addr)
> +arch_set_bit(long nr, volatile unsigned long *addr)
>  {
>  	if (IS_IMMEDIATE(nr)) {
>  		asm volatile(LOCK_PREFIX "orb %1,%0"
> @@ -78,32 +63,14 @@ set_bit(long nr, volatile unsigned long *addr)
>  	}
>  }
>  
> -/**
> - * __set_bit - Set a bit in memory
> - * @nr: the bit to set
> - * @addr: the address to start counting from
> - *
> - * Unlike set_bit(), this function is non-atomic and may be reordered.
> - * If it's called on the same region of memory simultaneously, the effect
> - * may be that only one operation succeeds.
> - */
> -static __always_inline void __set_bit(long nr, volatile unsigned long *addr)
> +static __always_inline void
> +arch___set_bit(long nr, volatile unsigned long *addr)
>  {
>  	asm volatile(__ASM_SIZE(bts) " %1,%0" : : ADDR, "Ir" (nr) : "memory");
>  }
>  
> -/**
> - * clear_bit - Clears a bit in memory
> - * @nr: Bit to clear
> - * @addr: Address to start counting from
> - *
> - * clear_bit() is atomic and may not be reordered.  However, it does
> - * not contain a memory barrier, so if it is used for locking purposes,
> - * you should call smp_mb__before_atomic() and/or smp_mb__after_atomic()
> - * in order to ensure changes are visible on other processors.
> - */
>  static __always_inline void
> -clear_bit(long nr, volatile unsigned long *addr)
> +arch_clear_bit(long nr, volatile unsigned long *addr)
>  {
>  	if (IS_IMMEDIATE(nr)) {
>  		asm volatile(LOCK_PREFIX "andb %1,%0"
> @@ -115,26 +82,21 @@ clear_bit(long nr, volatile unsigned long *addr)
>  	}
>  }
>  
> -/*
> - * clear_bit_unlock - Clears a bit in memory
> - * @nr: Bit to clear
> - * @addr: Address to start counting from
> - *
> - * clear_bit() is atomic and implies release semantics before the memory
> - * operation. It can be used for an unlock.
> - */
> -static __always_inline void clear_bit_unlock(long nr, volatile unsigned long *addr)
> +static __always_inline void
> +arch_clear_bit_unlock(long nr, volatile unsigned long *addr)
>  {
>  	barrier();
> -	clear_bit(nr, addr);
> +	arch_clear_bit(nr, addr);
>  }
>  
> -static __always_inline void __clear_bit(long nr, volatile unsigned long *addr)
> +static __always_inline void
> +arch___clear_bit(long nr, volatile unsigned long *addr)
>  {
>  	asm volatile(__ASM_SIZE(btr) " %1,%0" : : ADDR, "Ir" (nr) : "memory");
>  }
>  
> -static __always_inline bool clear_bit_unlock_is_negative_byte(long nr, volatile unsigned long *addr)
> +static __always_inline bool
> +arch_clear_bit_unlock_is_negative_byte(long nr, volatile unsigned long *addr)
>  {
>  	bool negative;
>  	asm volatile(LOCK_PREFIX "andb %2,%1"
> @@ -143,48 +105,23 @@ static __always_inline bool clear_bit_unlock_is_negative_byte(long nr, volatile
>  		: "ir" ((char) ~(1 << nr)) : "memory");
>  	return negative;
>  }
> +#define arch_clear_bit_unlock_is_negative_byte                                 \
> +	arch_clear_bit_unlock_is_negative_byte
>  
> -// Let everybody know we have it
> -#define clear_bit_unlock_is_negative_byte clear_bit_unlock_is_negative_byte
> -
> -/*
> - * __clear_bit_unlock - Clears a bit in memory
> - * @nr: Bit to clear
> - * @addr: Address to start counting from
> - *
> - * __clear_bit() is non-atomic and implies release semantics before the memory
> - * operation. It can be used for an unlock if no other CPUs can concurrently
> - * modify other bits in the word.
> - */
> -static __always_inline void __clear_bit_unlock(long nr, volatile unsigned long *addr)
> +static __always_inline void
> +arch___clear_bit_unlock(long nr, volatile unsigned long *addr)
>  {
> -	__clear_bit(nr, addr);
> +	arch___clear_bit(nr, addr);
>  }
>  
> -/**
> - * __change_bit - Toggle a bit in memory
> - * @nr: the bit to change
> - * @addr: the address to start counting from
> - *
> - * Unlike change_bit(), this function is non-atomic and may be reordered.
> - * If it's called on the same region of memory simultaneously, the effect
> - * may be that only one operation succeeds.
> - */
> -static __always_inline void __change_bit(long nr, volatile unsigned long *addr)
> +static __always_inline void
> +arch___change_bit(long nr, volatile unsigned long *addr)
>  {
>  	asm volatile(__ASM_SIZE(btc) " %1,%0" : : ADDR, "Ir" (nr) : "memory");
>  }
>  
> -/**
> - * change_bit - Toggle a bit in memory
> - * @nr: Bit to change
> - * @addr: Address to start counting from
> - *
> - * change_bit() is atomic and may not be reordered.
> - * Note that @nr may be almost arbitrarily large; this function is not
> - * restricted to acting on a single-word quantity.
> - */
> -static __always_inline void change_bit(long nr, volatile unsigned long *addr)
> +static __always_inline void
> +arch_change_bit(long nr, volatile unsigned long *addr)
>  {
>  	if (IS_IMMEDIATE(nr)) {
>  		asm volatile(LOCK_PREFIX "xorb %1,%0"
> @@ -196,42 +133,20 @@ static __always_inline void change_bit(long nr, volatile unsigned long *addr)
>  	}
>  }
>  
> -/**
> - * test_and_set_bit - Set a bit and return its old value
> - * @nr: Bit to set
> - * @addr: Address to count from
> - *
> - * This operation is atomic and cannot be reordered.
> - * It also implies a memory barrier.
> - */
> -static __always_inline bool test_and_set_bit(long nr, volatile unsigned long *addr)
> +static __always_inline bool
> +arch_test_and_set_bit(long nr, volatile unsigned long *addr)
>  {
>  	return GEN_BINARY_RMWcc(LOCK_PREFIX __ASM_SIZE(bts), *addr, c, "Ir", nr);
>  }
>  
> -/**
> - * test_and_set_bit_lock - Set a bit and return its old value for lock
> - * @nr: Bit to set
> - * @addr: Address to count from
> - *
> - * This is the same as test_and_set_bit on x86.
> - */
>  static __always_inline bool
> -test_and_set_bit_lock(long nr, volatile unsigned long *addr)
> +arch_test_and_set_bit_lock(long nr, volatile unsigned long *addr)
>  {
> -	return test_and_set_bit(nr, addr);
> +	return arch_test_and_set_bit(nr, addr);
>  }
>  
> -/**
> - * __test_and_set_bit - Set a bit and return its old value
> - * @nr: Bit to set
> - * @addr: Address to count from
> - *
> - * This operation is non-atomic and can be reordered.
> - * If two examples of this operation race, one can appear to succeed
> - * but actually fail.  You must protect multiple accesses with a lock.
> - */
> -static __always_inline bool __test_and_set_bit(long nr, volatile unsigned long *addr)
> +static __always_inline bool
> +arch___test_and_set_bit(long nr, volatile unsigned long *addr)
>  {
>  	bool oldbit;
>  
> @@ -242,28 +157,13 @@ static __always_inline bool __test_and_set_bit(long nr, volatile unsigned long *
>  	return oldbit;
>  }
>  
> -/**
> - * test_and_clear_bit - Clear a bit and return its old value
> - * @nr: Bit to clear
> - * @addr: Address to count from
> - *
> - * This operation is atomic and cannot be reordered.
> - * It also implies a memory barrier.
> - */
> -static __always_inline bool test_and_clear_bit(long nr, volatile unsigned long *addr)
> +static __always_inline bool
> +arch_test_and_clear_bit(long nr, volatile unsigned long *addr)
>  {
>  	return GEN_BINARY_RMWcc(LOCK_PREFIX __ASM_SIZE(btr), *addr, c, "Ir", nr);
>  }
>  
> -/**
> - * __test_and_clear_bit - Clear a bit and return its old value
> - * @nr: Bit to clear
> - * @addr: Address to count from
> - *
> - * This operation is non-atomic and can be reordered.
> - * If two examples of this operation race, one can appear to succeed
> - * but actually fail.  You must protect multiple accesses with a lock.
> - *
> +/*
>   * Note: the operation is performed atomically with respect to
>   * the local CPU, but not other CPUs. Portable code should not
>   * rely on this behaviour.
> @@ -271,7 +171,8 @@ static __always_inline bool test_and_clear_bit(long nr, volatile unsigned long *
>   * accessed from a hypervisor on the same CPU if running in a VM: don't change
>   * this without also updating arch/x86/kernel/kvm.c
>   */
> -static __always_inline bool __test_and_clear_bit(long nr, volatile unsigned long *addr)
> +static __always_inline bool
> +arch___test_and_clear_bit(long nr, volatile unsigned long *addr)
>  {
>  	bool oldbit;
>  
> @@ -282,8 +183,8 @@ static __always_inline bool __test_and_clear_bit(long nr, volatile unsigned long
>  	return oldbit;
>  }
>  
> -/* WARNING: non atomic and it can be reordered! */
> -static __always_inline bool __test_and_change_bit(long nr, volatile unsigned long *addr)
> +static __always_inline bool
> +arch___test_and_change_bit(long nr, volatile unsigned long *addr)
>  {
>  	bool oldbit;
>  
> @@ -295,15 +196,8 @@ static __always_inline bool __test_and_change_bit(long nr, volatile unsigned lon
>  	return oldbit;
>  }
>  
> -/**
> - * test_and_change_bit - Change a bit and return its old value
> - * @nr: Bit to change
> - * @addr: Address to count from
> - *
> - * This operation is atomic and cannot be reordered.
> - * It also implies a memory barrier.
> - */
> -static __always_inline bool test_and_change_bit(long nr, volatile unsigned long *addr)
> +static __always_inline bool
> +arch_test_and_change_bit(long nr, volatile unsigned long *addr)
>  {
>  	return GEN_BINARY_RMWcc(LOCK_PREFIX __ASM_SIZE(btc), *addr, c, "Ir", nr);
>  }
> @@ -326,16 +220,7 @@ static __always_inline bool variable_test_bit(long nr, volatile const unsigned l
>  	return oldbit;
>  }
>  
> -#if 0 /* Fool kernel-doc since it doesn't do macros yet */
> -/**
> - * test_bit - Determine whether a bit is set
> - * @nr: bit number to test
> - * @addr: Address to start counting from
> - */
> -static bool test_bit(int nr, const volatile unsigned long *addr);
> -#endif
> -
> -#define test_bit(nr, addr)			\
> +#define arch_test_bit(nr, addr)			\
>  	(__builtin_constant_p((nr))		\
>  	 ? constant_test_bit((nr), (addr))	\
>  	 : variable_test_bit((nr), (addr)))
> @@ -504,6 +389,8 @@ static __always_inline int fls64(__u64 x)
>  
>  #include <asm-generic/bitops/const_hweight.h>
>  
> +#include <asm-generic/bitops-instrumented.h>
> +
>  #include <asm-generic/bitops/le.h>
>  
>  #include <asm-generic/bitops/ext2-atomic-setbit.h>
> diff --git a/include/asm-generic/bitops-instrumented.h b/include/asm-generic/bitops-instrumented.h
> new file mode 100644
> index 000000000000..ddd1c6d9d8db
> --- /dev/null
> +++ b/include/asm-generic/bitops-instrumented.h
> @@ -0,0 +1,263 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +/*
> + * This file provides wrappers with sanitizer instrumentation for bit
> + * operations.
> + *
> + * To use this functionality, an arch's bitops.h file needs to define each of
> + * the below bit operations with an arch_ prefix (e.g. arch_set_bit(),
> + * arch___set_bit(), etc.).
> + */
> +#ifndef _ASM_GENERIC_BITOPS_INSTRUMENTED_H
> +#define _ASM_GENERIC_BITOPS_INSTRUMENTED_H
> +
> +#include <linux/kasan-checks.h>
> +
> +/**
> + * set_bit - Atomically set a bit in memory
> + * @nr: the bit to set
> + * @addr: the address to start counting from
> + *
> + * This is a relaxed atomic operation (no implied memory barriers).
> + *
> + * Note that @nr may be almost arbitrarily large; this function is not
> + * restricted to acting on a single-word quantity.
> + */
> +static inline void set_bit(long nr, volatile unsigned long *addr)
> +{
> +	kasan_check_write(addr + BIT_WORD(nr), sizeof(long));
> +	arch_set_bit(nr, addr);
> +}
> +
> +/**
> + * __set_bit - Set a bit in memory
> + * @nr: the bit to set
> + * @addr: the address to start counting from
> + *
> + * Unlike set_bit(), this function is non-atomic. If it is called on the same
> + * region of memory concurrently, the effect may be that only one operation
> + * succeeds.
> + */
> +static inline void __set_bit(long nr, volatile unsigned long *addr)
> +{
> +	kasan_check_write(addr + BIT_WORD(nr), sizeof(long));
> +	arch___set_bit(nr, addr);
> +}
> +
> +/**
> + * clear_bit - Clears a bit in memory
> + * @nr: Bit to clear
> + * @addr: Address to start counting from
> + *
> + * This is a relaxed atomic operation (no implied memory barriers).
> + */
> +static inline void clear_bit(long nr, volatile unsigned long *addr)
> +{
> +	kasan_check_write(addr + BIT_WORD(nr), sizeof(long));
> +	arch_clear_bit(nr, addr);
> +}
> +
> +/**
> + * __clear_bit - Clears a bit in memory
> + * @nr: the bit to clear
> + * @addr: the address to start counting from
> + *
> + * Unlike clear_bit(), this function is non-atomic. If it is called on the same
> + * region of memory concurrently, the effect may be that only one operation
> + * succeeds.
> + */
> +static inline void __clear_bit(long nr, volatile unsigned long *addr)
> +{
> +	kasan_check_write(addr + BIT_WORD(nr), sizeof(long));
> +	arch___clear_bit(nr, addr);
> +}
> +
> +/**
> + * clear_bit_unlock - Clear a bit in memory, for unlock
> + * @nr: the bit to set
> + * @addr: the address to start counting from
> + *
> + * This operation is atomic and provides release barrier semantics.
> + */
> +static inline void clear_bit_unlock(long nr, volatile unsigned long *addr)
> +{
> +	kasan_check_write(addr + BIT_WORD(nr), sizeof(long));
> +	arch_clear_bit_unlock(nr, addr);
> +}
> +
> +/**
> + * __clear_bit_unlock - Clears a bit in memory
> + * @nr: Bit to clear
> + * @addr: Address to start counting from
> + *
> + * This is a non-atomic operation but implies a release barrier before the
> + * memory operation. It can be used for an unlock if no other CPUs can
> + * concurrently modify other bits in the word.
> + */
> +static inline void __clear_bit_unlock(long nr, volatile unsigned long *addr)
> +{
> +	kasan_check_write(addr + BIT_WORD(nr), sizeof(long));
> +	arch___clear_bit_unlock(nr, addr);
> +}
> +
> +/**
> + * change_bit - Toggle a bit in memory
> + * @nr: Bit to change
> + * @addr: Address to start counting from
> + *
> + * This is a relaxed atomic operation (no implied memory barriers).
> + *
> + * Note that @nr may be almost arbitrarily large; this function is not
> + * restricted to acting on a single-word quantity.
> + */
> +static inline void change_bit(long nr, volatile unsigned long *addr)
> +{
> +	kasan_check_write(addr + BIT_WORD(nr), sizeof(long));
> +	arch_change_bit(nr, addr);
> +}
> +
> +/**
> + * __change_bit - Toggle a bit in memory
> + * @nr: the bit to change
> + * @addr: the address to start counting from
> + *
> + * Unlike change_bit(), this function is non-atomic. If it is called on the same
> + * region of memory concurrently, the effect may be that only one operation
> + * succeeds.
> + */
> +static inline void __change_bit(long nr, volatile unsigned long *addr)
> +{
> +	kasan_check_write(addr + BIT_WORD(nr), sizeof(long));
> +	arch___change_bit(nr, addr);
> +}
> +
> +/**
> + * test_and_set_bit - Set a bit and return its old value
> + * @nr: Bit to set
> + * @addr: Address to count from
> + *
> + * This is an atomic fully-ordered operation (implied full memory barrier).
> + */
> +static inline bool test_and_set_bit(long nr, volatile unsigned long *addr)
> +{
> +	kasan_check_write(addr + BIT_WORD(nr), sizeof(long));
> +	return arch_test_and_set_bit(nr, addr);
> +}
> +
> +/**
> + * __test_and_set_bit - Set a bit and return its old value
> + * @nr: Bit to set
> + * @addr: Address to count from
> + *
> + * This operation is non-atomic. If two instances of this operation race, one
> + * can appear to succeed but actually fail.
> + */
> +static inline bool __test_and_set_bit(long nr, volatile unsigned long *addr)
> +{
> +	kasan_check_write(addr + BIT_WORD(nr), sizeof(long));
> +	return arch___test_and_set_bit(nr, addr);
> +}
> +
> +/**
> + * test_and_set_bit_lock - Set a bit and return its old value, for lock
> + * @nr: Bit to set
> + * @addr: Address to count from
> + *
> + * This operation is atomic and provides acquire barrier semantics if
> + * the returned value is 0.
> + * It can be used to implement bit locks.
> + */
> +static inline bool test_and_set_bit_lock(long nr, volatile unsigned long *addr)
> +{
> +	kasan_check_write(addr + BIT_WORD(nr), sizeof(long));
> +	return arch_test_and_set_bit_lock(nr, addr);
> +}
> +
> +/**
> + * test_and_clear_bit - Clear a bit and return its old value
> + * @nr: Bit to clear
> + * @addr: Address to count from
> + *
> + * This is an atomic fully-ordered operation (implied full memory barrier).
> + */
> +static inline bool test_and_clear_bit(long nr, volatile unsigned long *addr)
> +{
> +	kasan_check_write(addr + BIT_WORD(nr), sizeof(long));
> +	return arch_test_and_clear_bit(nr, addr);
> +}
> +
> +/**
> + * __test_and_clear_bit - Clear a bit and return its old value
> + * @nr: Bit to clear
> + * @addr: Address to count from
> + *
> + * This operation is non-atomic. If two instances of this operation race, one
> + * can appear to succeed but actually fail.
> + */
> +static inline bool __test_and_clear_bit(long nr, volatile unsigned long *addr)
> +{
> +	kasan_check_write(addr + BIT_WORD(nr), sizeof(long));
> +	return arch___test_and_clear_bit(nr, addr);
> +}
> +
> +/**
> + * test_and_change_bit - Change a bit and return its old value
> + * @nr: Bit to change
> + * @addr: Address to count from
> + *
> + * This is an atomic fully-ordered operation (implied full memory barrier).
> + */
> +static inline bool test_and_change_bit(long nr, volatile unsigned long *addr)
> +{
> +	kasan_check_write(addr + BIT_WORD(nr), sizeof(long));
> +	return arch_test_and_change_bit(nr, addr);
> +}
> +
> +/**
> + * __test_and_change_bit - Change a bit and return its old value
> + * @nr: Bit to change
> + * @addr: Address to count from
> + *
> + * This operation is non-atomic. If two instances of this operation race, one
> + * can appear to succeed but actually fail.
> + */
> +static inline bool __test_and_change_bit(long nr, volatile unsigned long *addr)
> +{
> +	kasan_check_write(addr + BIT_WORD(nr), sizeof(long));
> +	return arch___test_and_change_bit(nr, addr);
> +}
> +
> +/**
> + * test_bit - Determine whether a bit is set
> + * @nr: bit number to test
> + * @addr: Address to start counting from
> + */
> +static inline bool test_bit(long nr, const volatile unsigned long *addr)
> +{
> +	kasan_check_read(addr + BIT_WORD(nr), sizeof(long));
> +	return arch_test_bit(nr, addr);
> +}
> +
> +#if defined(arch_clear_bit_unlock_is_negative_byte)
> +/**
> + * clear_bit_unlock_is_negative_byte - Clear a bit in memory and test if bottom
> + *                                     byte is negative, for unlock.
> + * @nr: the bit to clear
> + * @addr: the address to start counting from
> + *
> + * This operation is atomic and provides release barrier semantics.
> + *
> + * This is a bit of a one-trick-pony for the filemap code, which clears
> + * PG_locked and tests PG_waiters,
> + */
> +static inline bool
> +clear_bit_unlock_is_negative_byte(long nr, volatile unsigned long *addr)
> +{
> +	kasan_check_write(addr + BIT_WORD(nr), sizeof(long));
> +	return arch_clear_bit_unlock_is_negative_byte(nr, addr);
> +}
> +/* Let everybody know we have it. */
> +#define clear_bit_unlock_is_negative_byte clear_bit_unlock_is_negative_byte
> +#endif
> +
> +#endif /* _ASM_GENERIC_BITOPS_INSTRUMENTED_H */
> -- 
> 2.22.0.rc1.257.g3120a18244-goog
>