linux-kernel - [BUG] new MIPS compile error on v5.15.27

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Date:   Thu, 10 Mar 2022 17:25:07 +0100
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Huang Pei <huangpei@...ngson.cn>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Sasha Levin <sashal@...nel.org>, Christoph Hellwig <hch@....de>
Cc:     stable@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>
Subject: [BUG] new MIPS compile error on v5.15.27

upstream commit 277c8cb3e8ac ("MIPS: fix local_{add,sub}_return on MIPS64")

was backported to v5.15.27 as

commit f98371d2ac83 ("MIPS: fix local_{add,sub}_return on MIPS64")

but breaks MIPS build:

In file included from ./arch/mips/include/asm/local.h:8:0,
                 from ./include/linux/genhd.h:20,
                 from ./include/linux/blkdev.h:8,
                 from ./include/linux/blk-cgroup.h:23,
                 from ./include/linux/writeback.h:14,
                 from ./include/linux/memcontrol.h:22,
                 from ./include/net/sock.h:53,
                 from ./include/linux/tcp.h:19,
                 from drivers/net/slip/slip.c:91:
./arch/mips/include/asm/asm.h:68:0: warning: "END" redefined
 #define END(function)     \
 
In file included from drivers/net/slip/slip.c:88:0:
drivers/net/slip/slip.h:44:0: note: this is the location of the previous definition
 #define END             0300  /* indicates end of frame */

Analyses reveals that with the backported MIPS fix there is a new
#include <asm/asm.h> introduced by ./arch/mips/include/asm/local.h
which already defines some END macro.

But why does v5.16.x compile fine where

commit a0ecfd10d669c ("MIPS: fix local_{add,sub}_return on MIPS64")

is also present since v5.16.3?

Deeper analyses shows that there is another patch introduced
in v5.16-rc1 which removed one #include in the above chain and
therefore does not define END by asm/asm.h:

commit 348332e000697 ("mm: don't include <linux/blk-cgroup.h> in <linux/writeback.h>")

Hence, the MIPS fix should only be applied to branches where
the mm fix is already present. Or the mm fix should be backported
as well (if it has no side-effects).

Note: the MIPS fix was apparently not (yet?) applied to v5.10.y or earlier
even tough the Fixes: 7232311ef14c ("local_t: mips extension")
would be true.

BR and thanks,
Nikolaus Schaller