drm/i915/userptr: Acquire the page lock around set_page_dirty()

set_page_dirty says:

	For pages with a mapping this should be done under the page lock
	for the benefit of asynchronous memory errors who prefer a
	consistent dirty state. This rule can be broken in some special
	cases, but should be better not to.

Under those rules, it is only safe for us to use the plain set_page_dirty
calls for shmemfs/anonymous memory. Userptr may be used with real
mappings and so needs to use the locked version (set_page_dirty_lock).

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=203317
Fixes: 1944115857b2 ("drm/i915: Introduce mapping of user pages into video memory (userptr) ioctl")
References: af4685341733 ("ext4: warn when page is dirtied without buffers")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: stable@vger.kernel.org
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190708140327.26825-1-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
index 16ccec7fb7da92f52c5f0436a9f35c393de7db1e..32d208ede343acac5b19ae5d90256ea9386e0f80 100644 (file)
--- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
@@ -665,7 +665,15 @@ i915_gem_userptr_put_pages(struct drm_i915_gem_object *obj,
 
        for_each_sgt_page(page, sgt_iter, pages) {
                if (obj->mm.dirty)
-                       set_page_dirty(page);
+                       /*
+                        * As this may not be anonymous memory (e.g. shmem)
+                        * but exist on a real mapping, we have to lock
+                        * the page in order to dirty it -- holding
+                        * the page reference is not sufficient to
+                        * prevent the inode from being truncated.
+                        * Play safe and take the lock.
+                        */
+                       set_page_dirty_lock(page);
 
                mark_page_accessed(page);
                put_page(page);