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17 May 2024, 11:00:25 UTC
Revision 3a5facd09da848193f5bcb0dea098a298bc1a29d authored by Will Deacon on 08 June 2016, 14:10:57 UTC, committed by Will Deacon on 15 June 2016, 08:51:36 UTC 
arm64: spinlock: fix spin_unlock_wait for LSE atomics
 
Commit d86b8da04dfa ("arm64: spinlock: serialise spin_unlock_wait against
concurrent lockers") fixed spin_unlock_wait for LL/SC-based atomics under
the premise that the LSE atomics (in particular, the LDADDA instruction)
are indivisible.

Unfortunately, these instructions are only indivisible when used with the
-AL (full ordering) suffix and, consequently, the same issue can
theoretically be observed with LSE atomics, where a later (in program
order) load can be speculated before the write portion of the atomic
operation.

This patch fixes the issue by performing a CAS of the lock once we've
established that it's unlocked, in much the same way as the LL/SC code.

Fixes: d86b8da04dfa ("arm64: spinlock: serialise spin_unlock_wait against concurrent lockers")
Signed-off-by: Will Deacon <will.deacon@arm.com>
1 parent 38b850a
History
Tip revision: 3a5facd09da848193f5bcb0dea098a298bc1a29d authored by Will Deacon on 08 June 2016, 14:10:57 UTC
arm64: spinlock: fix spin_unlock_wait for LSE atomics
Tip revision: 3a5facd
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