linux-kernel - [PATCH v2] drm/ttm: Fix compile error when CONFIG

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Message-ID: <20250604085121.324be8c1@gandalf.local.home>
Date: Wed, 4 Jun 2025 08:51:21 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Thomas Hellström <thomas.hellstrom@...ux.intel.com>,
 Linus Torvalds <torvalds@...ux-foundation.org>, Matthew Wilcox  
 <willy@...radead.org>, LKML <linux-kernel@...r.kernel.org>,
 linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>, Christian 
 Koenig <christian.koenig@....com>, Huang Rui  <ray.huang@....com>, Matthew
  Auld <matthew.auld@...el.com>, Matthew Brost  <matthew.brost@...el.com>,
 dri-devel@...ts.freedesktop.org, Maarten Lankhorst  
 <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>,
 Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>
Subject: [PATCH v2] drm/ttm: Fix compile error when CONFIG_SHMEM is not set

From: Steven Rostedt <rostedt@...dmis.org>

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.git/scripts/Makefile.vmlinux:91: vmlinux.unstripped] Error 1
make[2]: *** [/work/build/trace/nobackup/linux.git/Makefile:1241: vmlinux] Error 2
make[1]: *** [/work/build/trace/nobackup/linux.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_writeout()
and shmem_writeout() directly. The issue is that when CONFIG_SHMEM is not
defined, shmem_writeout() is also not defined.

The function ttm_backup_backup_page() called mapping->a_ops->writepage()
which was then changed to call shmem_writeout() directly.

Even before commit 84798514db50 ("mm: Remove swap_writepage() and
shmem_writepage()"), it didn't make sense to call anything other than
shmem_writeout() as the ttm_backup deals only with shmem folios.

Have DRM_TTM config option select SHMEM to guarantee that shmem_writeout()
is available.

Link: https://lore.kernel.org/all/20250602170500.48713a2b@gandalf.local.home/

Suggested-by: Hugh Dickins <hughd@...gle.com>
Fixes: 84798514db50 ("mm: Remove swap_writepage() and shmem_writepage()")
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
Changes since v1: https://lore.kernel.org/all/20250602170500.48713a2b@gandalf.local.home/

- Instead of adding a shmem_writeout() stub, just make CONFIG_DRM_TTM
  select CONFIG_SHMEM (Hugh Dickins)

 drivers/gpu/drm/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index f094797f3b2b..ded28c71d89c 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -188,6 +188,7 @@ source "drivers/gpu/drm/display/Kconfig"
 config DRM_TTM
 	tristate
 	depends on DRM && MMU
+	select SHMEM
 	help
 	  GPU memory management subsystem for devices with multiple
 	  GPU memory types. Will be enabled automatically if a device driver
-- 
2.47.2