Re: [PATCH 1/6] block: add queue_limits_start_update_trylock()

On Mon, Sep 07, 2026 at 03:39:24PM +0200, Jack Wang wrote:

From: Jack Wang <jinpu.wang@cloud.ionos.com>

Some callers must not wait for q->limits_lock, because they hold
something the current holder waits for.  md is one: its
check_sb_changes() runs with reconfig_mutex held, while a
queue_attr_store() holding limits_lock waits in blk_mq_freeze_queue()
for I/O that can be waiting for a superblock update needing that mutex.

Add a trylock variant of queue_limits_start_update() for them.

I don't think this is a good idea, please fix the lock ordering
instead.

Assisted-by: Claude:claude-opus-5

But if not please try to come up with helpers like this based on
your own.  We don't really need this amount of AI slop.

+ * Like queue_limits_start_update(), but fails instead of waiting when another
+ * update is in flight.  For callers that must not block on q->limits_lock
+ * because they hold something its current owner is waiting for.
+ *
+ * Context: process context.
+ */
+static inline bool
+queue_limits_start_update_trylock(struct request_queue *q,
+				  struct queue_limits *lim)
+	__cond_acquires(true, &q->limits_lock)
+{
+	if (!mutex_trylock(&q->limits_lock))
+		return false;
+
+	*lim = q->limits;
+
+	return true;
+}
+
 int queue_limits_commit_update_frozen(struct request_queue *q,
 		struct queue_limits *lim) __releases(&q->limits_lock);
 int queue_limits_commit_update(struct request_queue *q,
-- 
2.43.0

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