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.
Reported-by: Lionel Landwerlin lionel.g.landwerlin@intel.com Fixes: cb6d7c7dc7ff ("drm/i915/userptr: Acquire the page lock around set_page_dirty()") 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: stable@vger.kernel.org --- drivers/gpu/drm/i915/gem/i915_gem_userptr.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c index b9d2bb15e4a6..1ad2047a6dbd 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c @@ -672,7 +672,7 @@ i915_gem_userptr_put_pages(struct drm_i915_gem_object *obj, obj->mm.dirty = false;
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 @@ -680,8 +680,20 @@ i915_gem_userptr_put_pages(struct drm_i915_gem_object *obj, * 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_lock(page); + set_page_dirty(page); + unlock_page(page); + }
mark_page_accessed(page); put_page(page);