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authorMikulas Patocka <mpatocka@redhat.com>2022-08-26 16:17:08 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2022-08-26 19:30:25 +0300
commit8238b4579866b7c1bb99883cfe102a43db5506ff (patch)
treea61b3a10f1d6b53bc7c05b08b8b49bb84156ee2e /arch
parent4c612826bec1441214816827979b62f84a097e91 (diff)
downloadlinux-8238b4579866b7c1bb99883cfe102a43db5506ff.tar.xz
wait_on_bit: add an acquire memory barrier
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>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/include/asm/bitops.h21
1 files changed, 21 insertions, 0 deletions
diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
index 973c6bd17f98..0fe9de58af31 100644
--- a/arch/x86/include/asm/bitops.h
+++ b/arch/x86/include/asm/bitops.h
@@ -207,6 +207,20 @@ static __always_inline bool constant_test_bit(long nr, const volatile unsigned l
(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;
@@ -226,6 +240,13 @@ arch_test_bit(unsigned long nr, const volatile unsigned long *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