Am 19.03.22 um 08:31 schrieb Xiaomeng Tong:
When list_for_each_entry() completes the iteration over the whole list
without breaking the loop, the iterator value will be a bogus pointer
computed based on the head element.
While it is safe to use the pointer to determine if it was computed
based on the head element with &pos->member == head, using the iterator
variable after the loop should be avoided.
In preparation to limiting the scope of a list iterator to the list
traversal loop, use a dedicated pointer to point to the found element [1].
Link: https://lore.kernel.org/all/YhdfEIwI4EdtHdym@xxxxxxxxx/
Well exactly that's why I'm pushing back to those changes.
We have tons of cases like this and I certainly won't accept patches to
make the code more complex than necessary. Especially not adding extra
local variables.
Regards,
Christian.
Signed-off-by: Xiaomeng Tong <xiam0nd.tong@xxxxxxxxx>
---
drivers/gpu/drm/ttm/ttm_bo.c | 20 ++++++++++----------
1 file changed, 10 insertions(+), 10 deletions(-)
diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index db3dc7ef5382..413b5bbf2414 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -673,36 +673,36 @@ int ttm_mem_evict_first(struct ttm_device *bdev,
struct ww_acquire_ctx *ticket)
{
struct ttm_buffer_object *bo = NULL, *busy_bo = NULL;
+ struct ttm_buffer_object *iter;
bool locked = false;
unsigned i;
int ret;
spin_lock(&bdev->lru_lock);
for (i = 0; i < TTM_MAX_BO_PRIORITY; ++i) {
- list_for_each_entry(bo, &man->lru[i], lru) {
+ list_for_each_entry(iter, &man->lru[i], lru) {
bool busy;
- if (!ttm_bo_evict_swapout_allowable(bo, ctx, place,
+ if (!ttm_bo_evict_swapout_allowable(iter, ctx, place,
&locked, &busy)) {
if (busy && !busy_bo && ticket !=
- dma_resv_locking_ctx(bo->base.resv))
- busy_bo = bo;
+ dma_resv_locking_ctx(iter->base.resv))
+ busy_bo = iter;
continue;
}
- if (!ttm_bo_get_unless_zero(bo)) {
+ if (!ttm_bo_get_unless_zero(iter)) {
if (locked)
- dma_resv_unlock(bo->base.resv);
+ dma_resv_unlock(iter->base.resv);
continue;
}
+
+ bo = iter;
break;
}
- /* If the inner loop terminated early, we have our candidate */
- if (&bo->lru != &man->lru[i])
+ if (bo)
break;
-
- bo = NULL;
}
if (!bo) {
