+ mm-fix-compile-error-when-config_shmem-is-not-set.patch added to mm-hotfixes-unstable branch

+ mm-fix-compile-error-when-config_shmem-is-not-set.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm: fix compile error when CONFIG_SHMEM is not set
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-fix-compile-error-when-config_shmem-is-not-set.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-fix-compile-error-when-config_shmem-is-not-set.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Steven Rostedt <rostedt@goodmis.org>
Subject: mm: fix compile error when CONFIG_SHMEM is not set
Date: Mon, 2 Jun 2025 17:05:00 -0400

When CONFIG_SHMEM is not set, the following compiler error occurs:

ld: vmlinux.o: in function `ttm_backup_backup_page':
(.text+0x10363bc): undefined reference to `shmem_writeout'
make[3]: *** [/work/build/trace/nobackup/linux-test.git/scripts/Makefile.vmlinux:91: vmlinux.unstripped] Error 1
make[2]: *** [/work/build/trace/nobackup/linux-test.git/Makefile:1241: vmlinux] Error 2
make[1]: *** [/work/build/trace/nobackup/linux-test.git/Makefile:248: __sub-make] Error 2
make[1]: Leaving directory '/work/build/nobackup/tracetest'
make: *** [Makefile:248: __sub-make] Error 2

This is due to the replacement of writepage and calling swap_writepage()
and shmem_writepage() directly.  The issue is that when CONFIG_SHMEM is
not defined, shmem_writepage() is also not defined.  Add it as a stub, and
it should also never be called when CONFIG_SHMEM is undefined.

Link: https://lkml.kernel.org/r/20250602170500.48713a2b@gandalf.local.home
Fixes: 84798514db50 ("mm: Remove swap_writepage() and shmem_writepage()")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/shmem.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/mm/shmem.c~mm-fix-compile-error-when-config_shmem-is-not-set
+++ a/mm/shmem.c
@@ -5760,6 +5760,11 @@ void shmem_unlock_mapping(struct address
 {
 }
 
+int shmem_writeout(struct folio *folio, struct writeback_control *wbc)
+{
+	return 0;
+}
+
 #ifdef CONFIG_MMU
 unsigned long shmem_get_unmapped_area(struct file *file,
 				      unsigned long addr, unsigned long len,
_

Patches currently in -mm which might be from rostedt@goodmis.org are

mm-fix-compile-error-when-config_shmem-is-not-set.patch