linux-kernel - [tip: locking/core] locking/atomic: atomic64: Remove unusable atomic ops

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Date:   Mon, 13 Dec 2021 10:03:20 -0000
From:   "tip-bot2 for Mark Rutland" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     kernel test robot <lkp@...el.com>,
        Mark Rutland <mark.rutland@....com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Boqun Feng <boqun.feng@...il.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: locking/core] locking/atomic: atomic64: Remove unusable atomic ops

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     5fb6e8cf53b005d287d4c2d137a415ff7d025a81
Gitweb:        https://git.kernel.org/tip/5fb6e8cf53b005d287d4c2d137a415ff7d025a81
Author:        Mark Rutland <mark.rutland@....com>
AuthorDate:    Fri, 26 Nov 2021 11:59:23 
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Mon, 13 Dec 2021 10:56:09 +01:00

locking/atomic: atomic64: Remove unusable atomic ops

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>
Signed-off-by: Mark Rutland <mark.rutland@....com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Boqun Feng <boqun.feng@...il.com>
Link: https://lore.kernel.org/r/20211126115923.41489-1-mark.rutland@arm.com
---
 lib/atomic64.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/lib/atomic64.c b/lib/atomic64.c
index 3df6539..caf8957 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)