[PATCH 5.19] wait_on_bit: add an acquire memory barrier

27 Oct 2022

commit 8238b4579866b7c1bb99883cfe102a43db5506ff upstream.
There are several places in the kernel where wait_on_bit is not followed
by a memory barrier (for example, in drivers/md/dm-bufio.c:new_read).
On architectures with weak memory ordering, it may happen that memory
accesses that follow wait_on_bit are reordered before wait_on_bit and
they may return invalid data.
Fix this class of bugs by introducing a new function "test_bit_acquire"
that works like test_bit, but has acquire memory ordering semantics.
Signed-off-by: Mikulas Patocka mpatocka@redhat.com
Acked-by: Will Deacon will@kernel.org
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds torvalds@linux-foundation.org
---
 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                       |    6 +++++
 arch/s390/include/asm/bitops.h                       |    7 ++++++
 arch/sh/include/asm/bitops-op32.h                    |    7 ++++++
 arch/x86/include/asm/bitops.h                        |   21 +++++++++++++++++++
 include/asm-generic/bitops/instrumented-non-atomic.h |   12 ++++++++++
 include/asm-generic/bitops/non-atomic.h              |   14 ++++++++++++
 include/linux/buffer_head.h                          |    2 -
 include/linux/wait_bit.h                             |    8 +++----
 kernel/sched/wait_bit.c                              |    2 -
 12 files changed, 102 insertions(+), 6 deletions(-)
Index: linux-stable/arch/x86/include/asm/bitops.h
===================================================================

--- linux-stable.orig/arch/x86/include/asm/bitops.h	2022-10-17 19:02:15.000000000 +0200
+++ linux-stable/arch/x86/include/asm/bitops.h	2022-10-17 19:02:15.000000000 +0200
@@ -207,6 +207,20 @@ static __always_inline bool constant_tes
    	(addr[nr >> _BITOPS_LONG_SHIFT])) != 0;
 }
+static __always_inline bool constant_test_bit_acquire(long nr, const volatile unsigned long *addr)
+{
+	bool oldbit;
+
+	asm volatile("testb %2,%1"
+		     CC_SET(nz)
+		     : CC_OUT(nz) (oldbit)
+		     : "m" (((unsigned char *)addr)[nr >> 3]),
+		       "i" (1 << (nr & 7))
+		     :"memory");
+
+	return oldbit;
+}
+
 static __always_inline bool variable_test_bit(long nr, volatile const unsigned long *addr)
 {
    bool oldbit;
@@ -224,6 +238,13 @@ static __always_inline bool variable_tes
     ? constant_test_bit((nr), (addr))	\
     : variable_test_bit((nr), (addr)))
+static __always_inline bool
+arch_test_bit_acquire(unsigned long nr, const volatile unsigned long *addr)
+{
+	return __builtin_constant_p(nr) ? constant_test_bit_acquire(nr, addr) :
+					  variable_test_bit(nr, addr);
+}
+
 /**
  * __ffs - find first set bit in word
  * @word: The word to search
Index: linux-stable/include/asm-generic/bitops/instrumented-non-atomic.h
===================================================================
--- linux-stable.orig/include/asm-generic/bitops/instrumented-non-atomic.h	2022-10-17 19:02:15.000000000 +0200
+++ linux-stable/include/asm-generic/bitops/instrumented-non-atomic.h	2022-10-17 19:02:15.000000000 +0200
@@ -135,4 +135,16 @@ static __always_inline bool test_bit(lon
    return arch_test_bit(nr, addr);
 }
+/**
+ * _test_bit_acquire - Determine, with acquire semantics, whether a bit is set
+ * @nr: bit number to test
+ * @addr: Address to start counting from
+ */
+static __always_inline bool
+test_bit_acquire(unsigned long nr, const volatile unsigned long *addr)
+{
+	instrument_atomic_read(addr + BIT_WORD(nr), sizeof(long));
+	return arch_test_bit_acquire(nr, addr);
+}
+
 #endif /* _ASM_GENERIC_BITOPS_INSTRUMENTED_NON_ATOMIC_H */
Index: linux-stable/include/asm-generic/bitops/non-atomic.h
===================================================================
--- linux-stable.orig/include/asm-generic/bitops/non-atomic.h	2022-10-17 19:02:15.000000000 +0200
+++ linux-stable/include/asm-generic/bitops/non-atomic.h	2022-10-17 19:02:15.000000000 +0200
@@ -3,6 +3,7 @@
 #define _ASM_GENERIC_BITOPS_NON_ATOMIC_H_
#include <asm/types.h>
+#include <asm/barrier.h>
/**
  * arch___set_bit - Set a bit in memory
@@ -119,4 +120,17 @@ arch_test_bit(unsigned int nr, const vol
 }
 #define test_bit arch_test_bit
+/**
+ * arch_test_bit_acquire - Determine, with acquire semantics, whether a bit is set
+ * @nr: bit number to test
+ * @addr: Address to start counting from
+ */
+static __always_inline bool
+arch_test_bit_acquire(unsigned long nr, const volatile unsigned long *addr)
+{
+	unsigned long *p = ((unsigned long *)addr) + BIT_WORD(nr);
+	return 1UL & (smp_load_acquire(p) >> (nr & (BITS_PER_LONG-1)));
+}
+#define test_bit_acquire arch_test_bit_acquire
+
 #endif /* _ASM_GENERIC_BITOPS_NON_ATOMIC_H_ */
Index: linux-stable/include/linux/buffer_head.h
===================================================================
--- linux-stable.orig/include/linux/buffer_head.h	2022-10-17 19:02:15.000000000 +0200
+++ linux-stable/include/linux/buffer_head.h	2022-10-17 19:02:15.000000000 +0200
@@ -166,7 +166,7 @@ static __always_inline int buffer_uptoda
     * make it consistent with folio_test_uptodate
     * pairs with smp_mb__before_atomic in set_buffer_uptodate
     */
-	return (smp_load_acquire(&bh->b_state) & (1UL << BH_Uptodate)) != 0;
+	return test_bit_acquire(BH_Uptodate, &bh->b_state);
 }
#define bh_offset(bh)		((unsigned long)(bh)->b_data & ~PAGE_MASK)
Index: linux-stable/include/linux/wait_bit.h
===================================================================
--- linux-stable.orig/include/linux/wait_bit.h	2022-10-17 19:02:15.000000000 +0200
+++ linux-stable/include/linux/wait_bit.h	2022-10-17 19:02:15.000000000 +0200
@@ -71,7 +71,7 @@ static inline int
 wait_on_bit(unsigned long *word, int bit, unsigned mode)
 {
    might_sleep();
-	if (!test_bit(bit, word))
+	if (!test_bit_acquire(bit, word))
    	return 0;
    return out_of_line_wait_on_bit(word, bit,
    			       bit_wait,
@@ -96,7 +96,7 @@ static inline int
 wait_on_bit_io(unsigned long *word, int bit, unsigned mode)
 {
    might_sleep();
-	if (!test_bit(bit, word))
+	if (!test_bit_acquire(bit, word))
    	return 0;
    return out_of_line_wait_on_bit(word, bit,
    			       bit_wait_io,
@@ -123,7 +123,7 @@ wait_on_bit_timeout(unsigned long *word,
    	    unsigned long timeout)
 {
    might_sleep();
-	if (!test_bit(bit, word))
+	if (!test_bit_acquire(bit, word))
    	return 0;
    return out_of_line_wait_on_bit_timeout(word, bit,
    				       bit_wait_timeout,
@@ -151,7 +151,7 @@ wait_on_bit_action(unsigned long *word,
    	   unsigned mode)
 {
    might_sleep();
-	if (!test_bit(bit, word))
+	if (!test_bit_acquire(bit, word))
    	return 0;
    return out_of_line_wait_on_bit(word, bit, action, mode);
 }
Index: linux-stable/kernel/sched/wait_bit.c
===================================================================
--- linux-stable.orig/kernel/sched/wait_bit.c	2022-10-17 19:02:15.000000000 +0200
+++ linux-stable/kernel/sched/wait_bit.c	2022-10-17 19:02:15.000000000 +0200
@@ -47,7 +47,7 @@ __wait_on_bit(struct wait_queue_head *wq
    	prepare_to_wait(wq_head, &wbq_entry->wq_entry, mode);
    	if (test_bit(wbq_entry->key.bit_nr, wbq_entry->key.flags))
    		ret = (*action)(&wbq_entry->key, mode);
-	} while (test_bit(wbq_entry->key.bit_nr, wbq_entry->key.flags) && !ret);
+	} while (test_bit_acquire(wbq_entry->key.bit_nr, wbq_entry->key.flags) && !ret);
finish_wait(wq_head, &wbq_entry->wq_entry);
Index: linux-stable/arch/alpha/include/asm/bitops.h
===================================================================
--- linux-stable.orig/arch/alpha/include/asm/bitops.h	2022-10-17 19:02:15.000000000 +0200
+++ linux-stable/arch/alpha/include/asm/bitops.h	2022-10-17 19:02:15.000000000 +0200
@@ -289,6 +289,13 @@ test_bit(int nr, const volatile void * a
    return (1UL & (((const int *) addr)[nr >> 5] >> (nr & 31))) != 0UL;
 }
+static __always_inline bool
+test_bit_acquire(unsigned long nr, const volatile unsigned long *addr)
+{
+	unsigned long *p = ((unsigned long *)addr) + BIT_WORD(nr);
+	return 1UL & (smp_load_acquire(p) >> (nr & (BITS_PER_LONG-1)));
+}
+
 /*
  * ffz = Find First Zero in word. Undefined if no zero exists,
  * so code should check against ~0UL first..
Index: linux-stable/arch/hexagon/include/asm/bitops.h
===================================================================
--- linux-stable.orig/arch/hexagon/include/asm/bitops.h	2022-10-17 19:02:15.000000000 +0200
+++ linux-stable/arch/hexagon/include/asm/bitops.h	2022-10-17 19:02:15.000000000 +0200
@@ -172,7 +172,22 @@ static inline int __test_bit(int nr, con
    return retval;
 }
+static inline int __test_bit_acquire(int 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;
+}
+
 #define test_bit(nr, addr) __test_bit(nr, addr)
+#define test_bit_acquire(nr, addr) __test_bit_acquire(nr, addr)
/*
  * ffz - find first zero in word.
Index: linux-stable/arch/ia64/include/asm/bitops.h
===================================================================
--- linux-stable.orig/arch/ia64/include/asm/bitops.h	2022-10-17 19:02:15.000000000 +0200
+++ linux-stable/arch/ia64/include/asm/bitops.h	2022-10-17 19:02:15.000000000 +0200
@@ -337,6 +337,13 @@ test_bit (int nr, const volatile void *a
    return 1 & (((const volatile __u32 *) addr)[nr >> 5] >> (nr & 31));
 }
+static __always_inline bool
+test_bit_acquire(unsigned long nr, const volatile unsigned long *addr)
+{
+	unsigned long *p = ((unsigned long *)addr) + BIT_WORD(nr);
+	return 1UL & (smp_load_acquire(p) >> (nr & (BITS_PER_LONG-1)));
+}
+
 /**
  * ffz - find the first zero bit in a long word
  * @x: The long word to find the bit in
Index: linux-stable/arch/m68k/include/asm/bitops.h
===================================================================
--- linux-stable.orig/arch/m68k/include/asm/bitops.h	2022-10-17 19:02:15.000000000 +0200
+++ linux-stable/arch/m68k/include/asm/bitops.h	2022-10-17 19:02:15.000000000 +0200
@@ -153,6 +153,12 @@ static inline int test_bit(int nr, const
    return (vaddr[nr >> 5] & (1UL << (nr & 31))) != 0;
 }
+static __always_inline bool
+test_bit_acquire(unsigned long nr, const volatile unsigned long *addr)
+{
+	unsigned long *p = ((unsigned long *)addr) + BIT_WORD(nr);
+	return 1UL & (smp_load_acquire(p) >> (nr & (BITS_PER_LONG-1)));
+}
static inline int bset_reg_test_and_set_bit(int nr,
    				    volatile unsigned long *vaddr)
Index: linux-stable/arch/s390/include/asm/bitops.h
===================================================================
--- linux-stable.orig/arch/s390/include/asm/bitops.h	2022-10-17 19:02:15.000000000 +0200
+++ linux-stable/arch/s390/include/asm/bitops.h	2022-10-17 19:02:15.000000000 +0200
@@ -184,6 +184,13 @@ static inline bool arch_test_bit(unsigne
    return *addr & mask;
 }
+static __always_inline bool
+arch_test_bit_acquire(unsigned long nr, const volatile unsigned long *addr)
+{
+	unsigned long *p = ((unsigned long *)addr) + BIT_WORD(nr);
+	return 1UL & (smp_load_acquire(p) >> (nr & (BITS_PER_LONG-1)));
+}
+
 static inline bool arch_test_and_set_bit_lock(unsigned long nr,
    				      volatile unsigned long *ptr)
 {
Index: linux-stable/arch/sh/include/asm/bitops-op32.h
===================================================================
--- linux-stable.orig/arch/sh/include/asm/bitops-op32.h	2022-10-17 19:02:15.000000000 +0200
+++ linux-stable/arch/sh/include/asm/bitops-op32.h	2022-10-17 19:02:15.000000000 +0200
@@ -138,4 +138,11 @@ static inline int test_bit(int nr, const
    return 1UL & (addr[BIT_WORD(nr)] >> (nr & (BITS_PER_LONG-1)));
 }
+static __always_inline bool
+test_bit_acquire(unsigned long nr, const volatile unsigned long *addr)
+{
+	unsigned long *p = ((unsigned long *)addr) + BIT_WORD(nr);
+	return 1UL & (smp_load_acquire(p) >> (nr & (BITS_PER_LONG-1)));
+}
+
 #endif /* __ASM_SH_BITOPS_OP32_H */

    

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[PATCH 5.19] wait_on_bit: add an acquire memory barrier