From: Chris Wilson chris@chris-wilson.co.uk
commit 2d691aeca4aecbb8d0414a777a46981a8e142b05 upstream.
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).
However, following a try_to_unmap() we may want to remove the userptr and so call put_pages(). However, try_to_unmap() acquires the page lock and so we must avoid recursively locking the pages ourselves -- which means that we cannot safely acquire the lock around set_page_dirty(). Since we can't be sure of the lock, we have to risk skip dirtying the page, or else risk calling set_page_dirty() without a lock and so risk fs corruption.
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=203317 Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=112012 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: Lionel Landwerlin lionel.g.landwerlin@intel.com Cc: Tvrtko Ursulin tvrtko.ursulin@intel.com Cc: Joonas Lahtinen joonas.lahtinen@linux.intel.com Cc: stable@vger.kernel.org Reviewed-by: Tvrtko Ursulin tvrtko.ursulin@intel.com Link: https://patchwork.freedesktop.org/patch/msgid/20191111133205.11590-1-chris@c... (cherry picked from commit 0d4bbe3d407f79438dc4f87943db21f7134cfc65) Signed-off-by: Joonas Lahtinen joonas.lahtinen@linux.intel.com (cherry picked from commit cee7fb437edcdb2f9f8affa959e274997f5dca4d) Signed-off-by: Rodrigo Vivi rodrigo.vivi@intel.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/gpu/drm/i915/i915_gem_userptr.c | 22 +++++++++++++++++++++- 1 file changed, 21 insertions(+), 1 deletion(-)
--- a/drivers/gpu/drm/i915/i915_gem_userptr.c +++ b/drivers/gpu/drm/i915/i915_gem_userptr.c @@ -690,8 +690,28 @@ i915_gem_userptr_put_pages(struct drm_i9 i915_gem_gtt_finish_pages(obj, pages);
for_each_sgt_page(page, sgt_iter, pages) { - if (obj->mm.dirty) + if (obj->mm.dirty && trylock_page(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. + * + * However...! + * + * The mmu-notifier can be invalidated for a + * migrate_page, that is alreadying holding the lock + * on the page. Such a try_to_unmap() will result + * in us calling put_pages() and so recursively try + * to lock the page. We avoid that deadlock with + * a trylock_page() and in exchange we risk missing + * some page dirtying. + */ set_page_dirty(page); + unlock_page(page); + }
mark_page_accessed(page); put_page(page);