linux-kernel - [PATCH] locking/atomic: atomic64: remove unusable atomics

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Message-Id: <20211126115923.41489-1-mark.rutland@arm.com>
Date:   Fri, 26 Nov 2021 11:59:23 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>
Cc:     arnd@...db.de, boqun.feng@...il.com, lkp@...el.com,
        mark.rutland@....com, will@...nel.org
Subject: [PATCH] locking/atomic: atomic64: remove unusable atomics

The generic atomic64 implementation provides:

* atomic64_and_return()
* atomic64_or_return()
* atomic64_xor_return()

... but none of these exist in the standard atomic64 API as described by
scripts/atomic/atomics.tbl, and none of these have prototypes exposed by
<asm-generic/atomic64.h>.

The lkp kernel test robot noted this results in warnings when building with
W=1:

  lib/atomic64.c:82:5: warning: no previous prototype for 'generic_atomic64_and_return' [-Wmissing-prototypes]

  lib/atomic64.c:82:5: warning: no previous prototype for 'generic_atomic64_or_return' [-Wmissing-prototypes]

  lib/atomic64.c:82:5: warning: no previous prototype for 'generic_atomic64_xor_return' [-Wmissing-prototypes]

This appears to have been a thinko in commit:

  28aa2bda2211f432 ("locking/atomic: Implement atomic{,64,_long}_fetch_{add,sub,and,andnot,or,xor}{,_relaxed,_acquire,_release}()")

... where we grouped add/sub separately from and/ox/xor, so that we could avoid
implementing _return forms for the latter group, but forgot to remove
ATOMIC64_OP_RETURN() for that group.

This doesn't cause any functional problem, but it's pointless to build code
which cannot be used. Remove the unusable code. This does not affect add/sub,
for which _return forms will still be built.

Reported-by: kernel test robot <lkp@...el.com>
Link: https://lore.kernel.org/r/202111120712.RtQHZohY-lkp@intel.com
Signed-off-by: Mark Rutland <mark.rutland@....com>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Boqun Feng <boqun.feng@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Will Deacon <will@...nel.org>
---
 lib/atomic64.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/lib/atomic64.c b/lib/atomic64.c
index 3df653994177..caf895789a1e 100644
--- a/lib/atomic64.c
+++ b/lib/atomic64.c
@@ -118,7 +118,6 @@ ATOMIC64_OPS(sub, -=)
 #undef ATOMIC64_OPS
 #define ATOMIC64_OPS(op, c_op)						\
 	ATOMIC64_OP(op, c_op)						\
-	ATOMIC64_OP_RETURN(op, c_op)					\
 	ATOMIC64_FETCH_OP(op, c_op)
 
 ATOMIC64_OPS(and, &=)
@@ -127,7 +126,6 @@ ATOMIC64_OPS(xor, ^=)
 
 #undef ATOMIC64_OPS
 #undef ATOMIC64_FETCH_OP
-#undef ATOMIC64_OP_RETURN
 #undef ATOMIC64_OP
 
 s64 generic_atomic64_dec_if_positive(atomic64_t *v)
-- 
2.30.2