atomics/treewide: Make atomic_fetch_add_unless() optional

Several architectures these have a near-identical implementation based
on atomic_read() and atomic_cmpxchg() which we can instead define in
<linux/atomic.h>, so let's do so, using something close to the existing
x86 implementation with try_cmpxchg().

Where an architecture provides its own atomic_fetch_add_unless(), it
must define a preprocessor symbol for it. The instrumented atomics are
updated accordingly.

Note that arch/arc's existing atomic_fetch_add_unless() had redundant
barriers, as these are already present in its atomic_cmpxchg()
implementation.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <[email protected]>
Reviewed-by: Geert Uytterhoeven <[email protected]>
Reviewed-by: Will Deacon <[email protected]>
Acked-by: Geert Uytterhoeven <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Palmer Dabbelt <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vineet Gupta <[email protected]>
Link: https://lore.kernel.org/lkml/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

0 files changed, 0 insertions, 0 deletions