On 8/23/26 7:00 PM, Yu Kuai wrote:
@@ -257,20 +262,21 @@ static inline bool bio_issue_as_root_blkg(struct bio *bio)
* @blkcg: blkcg of interest
* @q: request_queue of interest
*
* Lookup a blkg for the @blkcg - @q pair, whether it is online or dying.
*
- * Must be called in a RCU critical section.
+ * Must be called with either RCU read lock or queue_lock held.
*
* This does not acquire a reference. The caller must already hold one, or
* have the blkg pinned by I/O.
*/
static inline struct blkcg_gq *blkg_lookup_any(struct blkcg *blkcg,
struct request_queue *q)
{
- RCU_LOCKDEP_WARN(!rcu_read_lock_held(),
- "blkg_lookup_any() requires an RCU read lock");
+ RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&
+ !lockdep_is_held(&q->queue_lock),
+ "blkg_lookup_any() requires an RCU read lock or
queue_lock");
return rhashtable_lookup(&q->blkg_hash, &blkcg->css.id,
blkg_hash_params);
}
The changes look good to me. However, rhashtable_lookup() is annotated
with __must_hold_shared(RCU). Since we now officially support Clang
context annotations in the block layer, compiling with the latest
Clang/LLVM generates a number of context warnings, for example:
block/blk-cgroup.h:277:9: warning: calling function 'rhashtable_lookup'
requires holding __ctx_lock_RCU 'RCU' [-Wthread-safety-analysis]
277 | return rhashtable_lookup(&q->blkg_hash, &blkcg->css.id,
| ^
The same warning is reported from several other block layer source
files that include blk-cgroup.h.
This indicates that rhashtable_lookup() requires the RCU read lock
from Clang's context-analysis perspective. Looking at the call paths of
blkg_lookup_any(), it appears that not all callers hold
rcu_read_lock() when invoking it.
I think we should fix those call paths to acquire rcu reader lock
before calling blkg_lookup_any(), rather than weakening or bypassing
the context annotation in blkg_lookup_any().
Thanks,
--Nilay
