[PATCH V3 6/6] blk-mq: manage hctx map via xarray

Ming Lei
2022-03-07T06:46:20Z

Firstly code becomes more clean by switching to xarray from plain array.

Secondly use-after-free on q->queue_hw_ctx can be fixed because
queue_for_each_hw_ctx() may be run when updating nr_hw_queues is
in-progress. With this patch, q->hctx_table is defined as xarray, and
this structure will share same lifetime with request queue, so
queue_for_each_hw_ctx() can use q->hctx_table to lookup hctx reliably.

Reported-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
block/blk-mq-tag.c | 2 +-
block/blk-mq.c | 55 ++++++++++++++++++------------------------
block/blk-mq.h | 2 +-
include/linux/blk-mq.h | 3 +--
include/linux/blkdev.h | 2 +-
5 files changed, 28 insertions(+), 36 deletions(-)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 1850a4225e12..68ac23d0b640 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -498,7 +498,7 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_tag_iter_fn *fn,
void *priv)
{
/*
- * __blk_mq_update_nr_hw_queues() updates nr_hw_queues and queue_hw_ctx
+ * __blk_mq_update_nr_hw_queues() updates nr_hw_queues and hctx_table
* while the queue is frozen. So we can use q_usage_counter to avoid
* racing with it.
*/
diff --git a/block/blk-mq.c b/block/blk-mq.c
index bffdd71c670d..a15d12fb227c 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -71,7 +71,8 @@ static int blk_mq_poll_stats_bkt(const struct request *rq)
static inline struct blk_mq_hw_ctx *blk_qc_to_hctx(struct request_queue *q,
blk_qc_t qc)
{
- return q->queue_hw_ctx[(qc & ~BLK_QC_T_INTERNAL) >> BLK_QC_T_SHIFT];
+ return xa_load(&q->hctx_table,
+ (qc & ~BLK_QC_T_INTERNAL) >> BLK_QC_T_SHIFT);
}

static inline struct request *blk_qc_to_rq(struct blk_mq_hw_ctx *hctx,
@@ -573,7 +574,7 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q,
* If not tell the caller that it should skip this queue.
*/
ret = -EXDEV;
- data.hctx = q->queue_hw_ctx[hctx_idx];
+ data.hctx = xa_load(&q->hctx_table, hctx_idx);
if (!blk_mq_hw_queue_mapped(data.hctx))
goto out_queue_exit;
cpu = cpumask_first_and(data.hctx->cpumask, cpu_online_mask);
@@ -3437,6 +3438,8 @@ static void blk_mq_exit_hctx(struct request_queue *q,

blk_mq_remove_cpuhp(hctx);

+ xa_erase(&q->hctx_table, hctx_idx);
+
spin_lock(&q->unused_hctx_lock);
list_add(&hctx->hctx_list, &q->unused_hctx_list);
spin_unlock(&q->unused_hctx_lock);
@@ -3476,8 +3479,15 @@ static int blk_mq_init_hctx(struct request_queue *q,
if (blk_mq_init_request(set, hctx->fq->flush_rq, hctx_idx,
hctx->numa_node))
goto exit_hctx;
+
+ if (xa_insert(&q->hctx_table, hctx_idx, hctx, GFP_KERNEL))
+ goto exit_flush_rq;
+
return 0;

+ exit_flush_rq:
+ if (set->ops->exit_request)
+ set->ops->exit_request(set, hctx->fq->flush_rq, hctx_idx);
exit_hctx:
if (set->ops->exit_hctx)
set->ops->exit_hctx(hctx, hctx_idx);
@@ -3856,7 +3866,7 @@ void blk_mq_release(struct request_queue *q)
kobject_put(&hctx->kobj);
}

- kfree(q->queue_hw_ctx);
+ xa_destroy(&q->hctx_table);

/*
* release .mq_kobj and sw queue's kobject now because
@@ -3946,45 +3956,28 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
struct request_queue *q)
{
int i, j, end;
- struct blk_mq_hw_ctx **hctxs = q->queue_hw_ctx;
-
- if (q->nr_hw_queues < set->nr_hw_queues) {
- struct blk_mq_hw_ctx **new_hctxs;
-
- new_hctxs = kcalloc_node(set->nr_hw_queues,
- sizeof(*new_hctxs), GFP_KERNEL,
- set->numa_node);
- if (!new_hctxs)
- return;
- if (hctxs)
- memcpy(new_hctxs, hctxs, q->nr_hw_queues *
- sizeof(*hctxs));
- q->queue_hw_ctx = new_hctxs;
- kfree(hctxs);
- hctxs = new_hctxs;
- }

/* protect against switching io scheduler */
mutex_lock(&q->sysfs_lock);
for (i = 0; i < set->nr_hw_queues; i++) {
int old_node;
int node = blk_mq_get_hctx_node(set, i);
- struct blk_mq_hw_ctx *old_hctx = hctxs[i];
+ struct blk_mq_hw_ctx *old_hctx = xa_load(&q->hctx_table, i);

if (old_hctx) {
old_node = old_hctx->numa_node;
blk_mq_exit_hctx(q, set, old_hctx, i);
}

- hctxs[i] = blk_mq_alloc_and_init_hctx(set, q, i, node);
- if (!hctxs[i]) {
+ if (!blk_mq_alloc_and_init_hctx(set, q, i, node)) {
+ struct blk_mq_hw_ctx *hctx;
+
if (!old_hctx)
break;
pr_warn("Allocate new hctx on node %d fails, fallback to previous one on node %d\n",
node, old_node);
- hctxs[i] = blk_mq_alloc_and_init_hctx(set, q, i,
- old_node);
- WARN_ON_ONCE(!hctxs[i]);
+ hctx = blk_mq_alloc_and_init_hctx(set, q, i, old_node);
+ WARN_ON_ONCE(!hctx);
}
}
/*
@@ -4001,12 +3994,10 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
}

for (; j < end; j++) {
- struct blk_mq_hw_ctx *hctx = hctxs[j];
+ struct blk_mq_hw_ctx *hctx = xa_load(&q->hctx_table, j);

- if (hctx) {
+ if (hctx)
blk_mq_exit_hctx(q, set, hctx, j);
- hctxs[j] = NULL;
- }
}
mutex_unlock(&q->sysfs_lock);
}
@@ -4046,6 +4037,8 @@ int blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
INIT_LIST_HEAD(&q->unused_hctx_list);
spin_lock_init(&q->unused_hctx_lock);

+ xa_init(&q->hctx_table);
+
blk_mq_realloc_hw_ctxs(set, q);
if (!q->nr_hw_queues)
goto err_hctxs;
@@ -4075,7 +4068,7 @@ int blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
return 0;

err_hctxs:
- kfree(q->queue_hw_ctx);
+ xa_destroy(&q->hctx_table);
q->nr_hw_queues = 0;
blk_mq_sysfs_deinit(q);
err_poll:
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 948791ea2a3e..2615bd58bad3 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -83,7 +83,7 @@ static inline struct blk_mq_hw_ctx *blk_mq_map_queue_type(struct request_queue *
enum hctx_type type,
unsigned int cpu)
{
- return q->queue_hw_ctx[q->tag_set->map[type].mq_map[cpu]];
+ return xa_load(&q->hctx_table, q->tag_set->map[type].mq_map[cpu]);
}

static inline enum hctx_type blk_mq_get_hctx_type(unsigned int flags)
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 3a41d50b85d3..7aa5c54901a9 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -917,8 +917,7 @@ static inline void *blk_mq_rq_to_pdu(struct request *rq)
}

#define queue_for_each_hw_ctx(q, hctx, i) \
- for ((i) = 0; (i) < (q)->nr_hw_queues && \
- ({ hctx = (q)->queue_hw_ctx[i]; 1; }); (i)++)
+ xa_for_each(&(q)->hctx_table, (i), (hctx))

#define hctx_for_each_ctx(hctx, ctx, i) \
for ((i) = 0; (i) < (hctx)->nr_ctx && \
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index f757f9c2871f..a53ae40aaded 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -355,7 +355,7 @@ struct request_queue {
unsigned int queue_depth;

/* hw dispatch queues */
- struct blk_mq_hw_ctx **queue_hw_ctx;
+ struct xarray hctx_table;
unsigned int nr_hw_queues;

/*
--
2.31.1