linux-kernel - "mm: fix lazyfree BUG_ON check in try_to_unmap

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Date:   Thu, 9 Mar 2017 13:29:08 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: "mm: fix lazyfree BUG_ON check in try_to_unmap_one()" build error

Hello Minchan,

/* I can't https://marc.info/?l=linux-kernel&m=148886631303107 thread
   in my mail box for some reason so the Reply-To message-id may be wrong. */



commit "mm: fix lazyfree BUG_ON check in try_to_unmap_one()"
(mmotm fd07630cbf59bead90046dd3e5cfd891e58e6987)


	if (VM_WARN_ON_ONCE(PageSwapBacked(page) !=
			PageSwapCache(page))) {
	...
	}


does not compile on !CONFIG_DEBUG_VM configs, because VM_WARN_ONCE() is

	#define BUILD_BUG_ON_INVALID(e) ((void)(sizeof((__force long)(e))))



In file included from ./include/linux/mmdebug.h:4:0,
                 from ./include/linux/mm.h:8,
                 from mm/rmap.c:48:
mm/rmap.c: In function ‘try_to_unmap_one’:
./include/linux/bug.h:45:33: error: void value not ignored as it ought to be
 #define BUILD_BUG_ON_INVALID(e) ((void)(sizeof((__force long)(e))))
                                 ^
./include/linux/mmdebug.h:49:31: note: in expansion of macro ‘BUILD_BUG_ON_INVALID’
 #define VM_WARN_ON_ONCE(cond) BUILD_BUG_ON_INVALID(cond)
                               ^~~~~~~~~~~~~~~~~~~~
mm/rmap.c:1416:8: note: in expansion of macro ‘VM_WARN_ON_ONCE’
    if (VM_WARN_ON_ONCE(PageSwapBacked(page) !=
        ^~~~~~~~~~~~~~~

	-ss