* Re: [PATCH 36/98] blk-mq: quiesce a queue that joins a quiesced tag set
[not found] ` <20261028164415.1262013-37-axboe@kernel.dk>
@ 2026-10-30 22:37 ` Nathan Chancellor
0 siblings, 0 replies; only message in thread
From: Nathan Chancellor @ 2026-10-30 22:37 UTC (permalink / raw)
To: Jens Axboe, Andreas Hindborg, Boqun Feng, Miguel Ojeda, Gary Guo
Cc: linux-block, Josef Bacik, rust-for-linux
Hi Rust for Linux folks,
I only added a small subset of you plus the mailing list, if I missed
anybody, please bring them in as necessary.
On Wed, Oct 28, 2026 at 10:41:39AM -0600, Jens Axboe wrote:
> From: Josef Bacik <josef@toxicpanda.com>
>
> blk_mq_quiesce_tagset() only quiesces the queues on the list at that
> moment. A queue added before blk_mq_unquiesce_tagset() runs unquiesced,
> and then gets unquiesced without ever having been quiesced, which trips
> the warning in blk_mq_unquiesce_queue(). NVMe gets there when a
> controller fails while its namespaces are being scanned.
>
> Count the quiesce calls in the tag set and quiesce a joining queue that
> many times, under a spinlock that also serializes the two functions. It
> can't be tag_list_lock, see commit 59e25ef2b413.
>
> Fixes: 414dd48e882c ("blk-mq: add tagset quiesce interface")
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
After this patch landed in -next as commit 71ec3c7d6db8 ("blk-mq:
quiesce a queue that joins a quiesced tag set"), I am seeing the
following build error:
$ make -skj"$(nproc)" ARCH=x86_64 LLVM=1 mrproper allmodconfig rust/kernel.o
error[E0277]: the trait bound `bindings::__BindgenOpaqueArray8<[u8; 72]>: pin_init::Zeroable` is not satisfied
--> rust/kernel/block/mq/tag_set.rs:41:49
|
41 | let tag_set: bindings::blk_mq_tag_set = pin_init::zeroed();
| ^^^^^^^^^^^^^^^^^^ the trait `pin_init::Zeroable` is not implemented for `bindings::__BindgenOpaqueArray8<[u8; 72]>`
|
= help: the following other types implement trait `pin_init::Zeroable`:
()
(A, B, C, D, E, F, G, H, I, J)
(B, C, D, E, F, G, H, I, J)
(C, D, E, F, G, H, I, J)
(D, E, F, G, H, I, J)
(E, F, G, H, I, J)
(F, G, H, I, J)
(G, H, I, J)
and 6359 others
= note: required for `bindings::spinlock` to implement `pin_init::Zeroable`
= note: 1 redundant requirement hidden
= note: required for `blk_mq_tag_set` to implement `pin_init::Zeroable`
note: required by a bound in `pin_init::zeroed`
--> rust/pin-init/src/lib.rs:1688:24
|
1688 | pub const fn zeroed<T: Zeroable>() -> T {
| ^^^^^^^^ required by this bound in `zeroed`
error: aborting due to 1 previous error
For more information about this error, try `rustc --explain E0277`.
make[4]: *** [rust/Makefile:799: rust/kernel.o] Error 1
...
> ---
> block/blk-mq.c | 22 ++++++++++++++++++++++
> include/linux/blk-mq.h | 6 ++++++
> 2 files changed, 28 insertions(+)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 6d3ea97f9a00..0e8449424c9a 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -336,12 +336,15 @@ void blk_mq_quiesce_tagset(struct blk_mq_tag_set *set)
> {
> struct request_queue *q;
>
> + spin_lock(&set->quiesce_lock);
> + set->quiesce_depth++;
> rcu_read_lock();
> list_for_each_entry_rcu(q, &set->tag_list, tag_set_list) {
> if (!blk_queue_skip_tagset_quiesce(q))
> blk_mq_quiesce_queue_nowait(q);
> }
> rcu_read_unlock();
> + spin_unlock(&set->quiesce_lock);
>
> blk_mq_wait_quiesce_done(set);
> }
> @@ -351,12 +354,16 @@ void blk_mq_unquiesce_tagset(struct blk_mq_tag_set *set)
> {
> struct request_queue *q;
>
> + spin_lock(&set->quiesce_lock);
> + if (set->quiesce_depth)
> + set->quiesce_depth--;
> rcu_read_lock();
> list_for_each_entry_rcu(q, &set->tag_list, tag_set_list) {
> if (!blk_queue_skip_tagset_quiesce(q))
> blk_mq_unquiesce_queue(q);
> }
> rcu_read_unlock();
> + spin_unlock(&set->quiesce_lock);
> }
> EXPORT_SYMBOL_GPL(blk_mq_unquiesce_tagset);
>
> @@ -4346,6 +4353,8 @@ static void blk_mq_del_queue_tag_set(struct request_queue *q)
> static void blk_mq_add_queue_tag_set(struct blk_mq_tag_set *set,
> struct request_queue *q)
> {
> + unsigned int i;
> +
> mutex_lock(&set->tag_list_lock);
>
> /*
> @@ -4359,7 +4368,18 @@ static void blk_mq_add_queue_tag_set(struct blk_mq_tag_set *set,
> }
> if (set->flags & BLK_MQ_F_TAG_QUEUE_SHARED)
> queue_set_hctx_shared(q, true);
> +
> + /*
> + * A queue that joins a quiesced tag set is quiesced like the others,
> + * and blk_mq_unquiesce_tagset() finds what it is going to undo.
> + */
> + spin_lock(&set->quiesce_lock);
> list_add_tail_rcu(&q->tag_set_list, &set->tag_list);
> + if (!blk_queue_skip_tagset_quiesce(q)) {
> + for (i = 0; i < set->quiesce_depth; i++)
> + blk_mq_quiesce_queue_nowait(q);
> + }
> + spin_unlock(&set->quiesce_lock);
>
> mutex_unlock(&set->tag_list_lock);
> }
> @@ -4928,6 +4948,8 @@ int blk_mq_alloc_tag_set(struct blk_mq_tag_set *set)
>
> mutex_init(&set->tag_list_lock);
> INIT_LIST_HEAD(&set->tag_list);
> + spin_lock_init(&set->quiesce_lock);
> + set->quiesce_depth = 0;
>
> return 0;
>
> diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
> index 5e130b282b42..aa3b35405edc 100644
> --- a/include/linux/blk-mq.h
> +++ b/include/linux/blk-mq.h
> @@ -523,6 +523,10 @@ enum hctx_type {
> * @tag_list_lock: Serializes tag_list accesses.
> * @tag_list: List of the request queues that use this tag set. See also
> * request_queue.tag_set_list.
> + * @quiesce_lock: Serializes blk_mq_[un]quiesce_tagset() against each other
> + * and against a request queue being added to @tag_list.
> + * @quiesce_depth: How often blk_mq_quiesce_tagset() has been called without
> + * blk_mq_unquiesce_tagset().
> * @srcu: Use as lock when type of the request queue is blocking
> * (BLK_MQ_F_BLOCKING).
> * @update_nr_hwq_lock:
> @@ -548,6 +552,8 @@ struct blk_mq_tag_set {
>
> struct mutex tag_list_lock;
> struct list_head tag_list;
> + spinlock_t quiesce_lock;
> + unsigned int quiesce_depth;
> struct srcu_struct *srcu;
>
> struct rw_semaphore update_nr_hwq_lock;
> --
> 2.56.0
>
--
Cheers,
Nathan
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