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@xxxxxxxxx>
Fixes: cb6d7c7dc7ff ("drm/i915/userptr: Acquire the page lock around set_page_dirty()")
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Lionel Landwerlin <lionel.g.landwerlin@xxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
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);
--
2.22.0
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