On 08/07/2019 15:03, Chris Wilson wrote:
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.
If the mapping doesn't provide a set_page_dirty a_op, then
just fall through and assume that it wants buffer_heads.
Under those rules, it 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: 5cc9ed4b9a7a ("drm/i915: Introduce mapping of user pages into video memory (userptr) ioctl")
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
drivers/gpu/drm/i915/gem/i915_gem_userptr.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
index 16ccec7fb7da..32d208ede343 100644
--- 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);
Not an expert but sounds plausible.
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Regards,
Tvrtko
