blk-mq: manage hctx map via xarray

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

Second 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>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220308073219.91173-7-ming.lei@redhat.com
[axboe: fix blk_mq_hw_ctx forward declaration]
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-mq-debugfs.h b/block/blk-mq-debugfs.h
index a68aa60..69918f4 100644 (file)
--- a/block/blk-mq-debugfs.h
+++ b/block/blk-mq-debugfs.h
@@ -6,6 +6,8 @@
 
 #include <linux/seq_file.h>
 
+struct blk_mq_hw_ctx;
+
 struct blk_mq_debugfs_attr {
        const char *name;
        umode_t mode;

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 1850a42..68ac23d 100644 (file)
--- 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 bffdd71..e8d6d7a 100644 (file)
--- 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
@@ -3945,46 +3955,28 @@ static struct blk_mq_hw_ctx *blk_mq_alloc_and_init_hctx(
 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;
-       }
+       struct blk_mq_hw_ctx *hctx;
+       unsigned long i, j;
 
        /* 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)) {
                        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);
                }
        }
        /*
@@ -3993,21 +3985,13 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
         */
        if (i != set->nr_hw_queues) {
                j = q->nr_hw_queues;
-               end = i;
        } else {
                j = i;
-               end = q->nr_hw_queues;
                q->nr_hw_queues = set->nr_hw_queues;
        }
 
-       for (; j < end; j++) {
-               struct blk_mq_hw_ctx *hctx = hctxs[j];
-
-               if (hctx) {
-                       blk_mq_exit_hctx(q, set, hctx, j);
-                       hctxs[j] = NULL;
-               }
-       }
+       xa_for_each_start(&q->hctx_table, j, hctx, j)
+               blk_mq_exit_hctx(q, set, hctx, j);
        mutex_unlock(&q->sysfs_lock);
 }
 
@@ -4046,6 +4030,8 @@ 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 +4061,7 @@ 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 948791e..2615bd5 100644 (file)
--- 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 3a41d50..7aa5c54 100644 (file)
--- 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 e19947d..d982171 100644 (file)
--- 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;
 
        /*