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@chris-wilson.co.uk Cc: Tvrtko Ursulin tvrtko.ursulin@intel.com Cc: stable@vger.kernel.org

---

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@intel.com

Regards,

Tvrtko