On 16/08/2022 13.14, Herbert Xu wrote:
Hector Martin marcan@marcan.st wrote:
This has been broken since the dawn of time, and it was incompletely fixed by 346c09f80459, which added the necessary barriers in the work execution path but failed to account for the missing barrier in the test_and_set_bit() failure case. Fix it by switching to atomic_long_fetch_or(), which does have unconditional barrier semantics regardless of whether the bit was already set or not (this is actually just test_and_set_bit() minus the early exit path).
test_and_set_bit is supposed to contain a full memory barrier. If it doesn't then your arch is broken and needs to be fixed.
Changing this one spot is pointless because such assumptions are all over the kernel.
Documentation/atomic_bitops.txt and the asm-generic implementaton disagree with you, so this isn't quite as simple as "your arch is broken" :-)
- Hector