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| author | Mikulas Patocka <mpatocka@redhat.com> | 2022-08-26 16:17:08 +0300 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2022-08-26 19:30:25 +0300 |
| commit | 8238b4579866b7c1bb99883cfe102a43db5506ff (patch) | |
| tree | a61b3a10f1d6b53bc7c05b08b8b49bb84156ee2e /Documentation | |
| parent | 4c612826bec1441214816827979b62f84a097e91 (diff) | |
| download | linux-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')
| -rw-r--r-- | Documentation/atomic_bitops.txt | 10 |
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. |