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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 /Documentation/atomic_bitops.txt
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 'Documentation/atomic_bitops.txt')
-rw-r--r--Documentation/atomic_bitops.txt10
1 files changed, 4 insertions, 6 deletions
diff --git a/Documentation/atomic_bitops.txt b/Documentation/atomic_bitops.txt
index d8b101c97031..edea4656c5c0 100644
--- a/Documentation/atomic_bitops.txt
+++ b/Documentation/atomic_bitops.txt
@@ -58,13 +58,11 @@ Like with atomic_t, the rule of thumb is:
- RMW operations that have a return value are fully ordered.
- - RMW operations that are conditional are unordered on FAILURE,
- otherwise the above rules apply. In the case of test_and_set_bit_lock(),
- if the bit in memory is unchanged by the operation then it is deemed to have
- failed.
+ - RMW operations that are conditional are fully ordered.
-Except for a successful test_and_set_bit_lock() which has ACQUIRE semantics and
-clear_bit_unlock() which has RELEASE semantics.
+Except for a successful test_and_set_bit_lock() which has ACQUIRE semantics,
+clear_bit_unlock() which has RELEASE semantics and test_bit_acquire which has
+ACQUIRE semantics.
Since a platform only has a single means of achieving atomic operations
the same barriers as for atomic_t are used, see atomic_t.txt.