[PATCH V9 0/7] blk-mq: fix races related with freeing queue

[PATCH V9 0/7] blk-mq: fix races related with freeing queue

[Ming Lei]

Hi,

Since 45a9c9d909b2 ("blk-mq: Fix a use-after-free"), run queue isn't
allowed during cleanup queue even though queue refcount is held.

This change has caused lots of kernel oops triggered in run queue path,
turns out it isn't easy to fix them all.

So move freeing of hw queue resources into hctx's release handler, then
the above issue is fixed. Meantime, this way is safe given freeing hw
queue resource doesn't require tags.

V3 covers more races.

V9:
	- fix one issue in patch 1 of V8 by put the queue usage counter in
	  early return branch
	- make patch 4 of V8 a bit clean, as suggested by Christoph and
	  Hannes

V8:
	- merge the 4th and 5th of V7 into one patch, as suggested by Christoph
	- drop the 9th patch

V7:
	- add reviewed-by and tested-by tag
	- rename "dead_hctx" as "unused_hctx"
	- check if there are live hctx in queue's release handler
	- only patch 6 is modified

V6:
	- remove previous SCSI patch which will be routed via SCSI tree
	- add reviewed-by tag
	- fix one related NVMe scan vs reset race

V5:
	- refactor blk_mq_alloc_and_init_hctx()
	- fix race related updating nr_hw_queues by always freeing hctx
	  after request queue is released

V4:
	- add patch for fixing potential use-after-free in blk_mq_update_nr_hw_queues
	- fix comment in the last patch

V3:
	- cancel q->requeue_work in queue's release handler
	- cancel hctx->run_work in hctx's release handler
	- add patch 1 for fixing race in plug code path
	- the last patch is added for avoiding to grab SCSI's refcont
	in IO path

V2:
	- moving freeing hw queue resources into hctx's release handler


Ming Lei (7):
  blk-mq: grab .q_usage_counter when queuing request from plug code path
  blk-mq: move cancel of requeue_work into blk_mq_release
  blk-mq: free hw queue's resource in hctx's release handler
  blk-mq: split blk_mq_alloc_and_init_hctx into two parts
  blk-mq: always free hctx after request queue is freed
  blk-mq: move cancel of hctx->run_work into blk_mq_hw_sysfs_release
  block: don't drain in-progress dispatch in blk_cleanup_queue()

 block/blk-core.c       |  23 +-----
 block/blk-mq-sched.c   |  12 +++-
 block/blk-mq-sysfs.c   |   8 +++
 block/blk-mq.c         | 189 ++++++++++++++++++++++++++++---------------------
 block/blk-mq.h         |   2 +-
 include/linux/blk-mq.h |   2 +
 include/linux/blkdev.h |   7 ++
 7 files changed, 139 insertions(+), 104 deletions(-)

Cc: Dongli Zhang <dongli.zhang@oracle.com>
Cc: James Smart <james.smart@broadcom.com>
Cc: Bart Van Assche <bart.vanassche@wdc.com>
Cc: linux-scsi@vger.kernel.org,
Cc: Martin K . Petersen <martin.petersen@oracle.com>,
Cc: Christoph Hellwig <hch@lst.de>,
Cc: James E . J . Bottomley <jejb@linux.vnet.ibm.com>,

-- 
2.9.5

[PATCH V9 1/7] blk-mq: grab .q_usage_counter when queuing request from plug code path

[Ming Lei]

Just like aio/io_uring, we need to grab 2 refcount for queuing one
request, one is for submission, another is for completion.

If the request isn't queued from plug code path, the refcount grabbed
in generic_make_request() serves for submission. In theroy, this
refcount should have been released after the sumission(async run queue)
is done. blk_freeze_queue() works with blk_sync_queue() together
for avoiding race between cleanup queue and IO submission, given async
run queue activities are canceled because hctx->run_work is scheduled with
the refcount held, so it is fine to not hold the refcount when
running the run queue work function for dispatch IO.

However, if request is staggered into plug list, and finally queued
from plug code path, the refcount in submission side is actually missed.
And we may start to run queue after queue is removed because the queue's
kobject refcount isn't guaranteed to be grabbed in flushing plug list
context, then kernel oops is triggered, see the following race:

blk_mq_flush_plug_list():
        blk_mq_sched_insert_requests()
                insert requests to sw queue or scheduler queue
                blk_mq_run_hw_queue

Because of concurrent run queue, all requests inserted above may be
completed before calling the above blk_mq_run_hw_queue. Then queue can
be freed during the above blk_mq_run_hw_queue().

Fixes the issue by grab .q_usage_counter before calling
blk_mq_sched_insert_requests() in blk_mq_flush_plug_list(). This way is
safe because the queue is absolutely alive before inserting request.

Cc: Dongli Zhang <dongli.zhang@oracle.com>
Cc: James Smart <james.smart@broadcom.com>
Cc: Bart Van Assche <bart.vanassche@wdc.com>
Cc: linux-scsi@vger.kernel.org,
Cc: Martin K . Petersen <martin.petersen@oracle.com>,
Cc: Christoph Hellwig <hch@lst.de>,
Cc: James E . J . Bottomley <jejb@linux.vnet.ibm.com>,
Tested-by: James Smart <james.smart@broadcom.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-mq-sched.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index aa6bc5c02643..c59babca6857 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -413,6 +413,14 @@ void blk_mq_sched_insert_requests(struct blk_mq_hw_ctx *hctx,
 				  struct list_head *list, bool run_queue_async)
 {
 	struct elevator_queue *e;
+	struct request_queue *q = hctx->queue;
+
+	/*
+	 * blk_mq_sched_insert_requests() is called from flush plug
+	 * context only, and hold one usage counter to prevent queue
+	 * from being released.
+	 */
+	percpu_ref_get(&q->q_usage_counter);
 
 	e = hctx->queue->elevator;
 	if (e && e->type->ops.insert_requests)
@@ -426,12 +434,14 @@ void blk_mq_sched_insert_requests(struct blk_mq_hw_ctx *hctx,
 		if (!hctx->dispatch_busy && !e && !run_queue_async) {
 			blk_mq_try_issue_list_directly(hctx, list);
 			if (list_empty(list))
-				return;
+				goto out;
 		}
 		blk_mq_insert_requests(hctx, ctx, list);
 	}
 
 	blk_mq_run_hw_queue(hctx, run_queue_async);
+ out:
+	percpu_ref_put(&q->q_usage_counter);
 }
 
 static void blk_mq_sched_free_tags(struct blk_mq_tag_set *set,
-- 
2.9.5

[PATCH V9 2/7] blk-mq: move cancel of requeue_work into blk_mq_release

[Ming Lei]

With holding queue's kobject refcount, it is safe for driver
to schedule requeue. However, blk_mq_kick_requeue_list() may
be called after blk_sync_queue() is done because of concurrent
requeue activities, then requeue work may not be completed when
freeing queue, and kernel oops is triggered.

So moving the cancel of requeue_work into blk_mq_release() for
avoiding race between requeue and freeing queue.

Cc: Dongli Zhang <dongli.zhang@oracle.com>
Cc: James Smart <james.smart@broadcom.com>
Cc: Bart Van Assche <bart.vanassche@wdc.com>
Cc: linux-scsi@vger.kernel.org,
Cc: Martin K . Petersen <martin.petersen@oracle.com>,
Cc: Christoph Hellwig <hch@lst.de>,
Cc: James E . J . Bottomley <jejb@linux.vnet.ibm.com>,
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: James Smart <james.smart@broadcom.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-core.c | 1 -
 block/blk-mq.c   | 2 ++
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index a55389ba8779..93dc588fabe2 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -237,7 +237,6 @@ void blk_sync_queue(struct request_queue *q)
 		struct blk_mq_hw_ctx *hctx;
 		int i;
 
-		cancel_delayed_work_sync(&q->requeue_work);
 		queue_for_each_hw_ctx(q, hctx, i)
 			cancel_delayed_work_sync(&hctx->run_work);
 	}
diff --git a/block/blk-mq.c b/block/blk-mq.c
index fc60ed7e940e..89781309a108 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2634,6 +2634,8 @@ void blk_mq_release(struct request_queue *q)
 	struct blk_mq_hw_ctx *hctx;
 	unsigned int i;
 
+	cancel_delayed_work_sync(&q->requeue_work);
+
 	/* hctx kobj stays in hctx */
 	queue_for_each_hw_ctx(q, hctx, i) {
 		if (!hctx)
-- 
2.9.5

[PATCH V9 3/7] blk-mq: free hw queue's resource in hctx's release handler

[Ming Lei]

Once blk_cleanup_queue() returns, tags shouldn't be used any more,
because blk_mq_free_tag_set() may be called. Commit 45a9c9d909b2
("blk-mq: Fix a use-after-free") fixes this issue exactly.

However, that commit introduces another issue. Before 45a9c9d909b2,
we are allowed to run queue during cleaning up queue if the queue's
kobj refcount is held. After that commit, queue can't be run during
queue cleaning up, otherwise oops can be triggered easily because
some fields of hctx are freed by blk_mq_free_queue() in blk_cleanup_queue().

We have invented ways for addressing this kind of issue before, such as:

	8dc765d438f1 ("SCSI: fix queue cleanup race before queue initialization is done")
	c2856ae2f315 ("blk-mq: quiesce queue before freeing queue")

But still can't cover all cases, recently James reports another such
kind of issue:

	https://marc.info/?l=linux-scsi&m=155389088124782&w=2

This issue can be quite hard to address by previous way, given
scsi_run_queue() may run requeues for other LUNs.

Fixes the above issue by freeing hctx's resources in its release handler, and this
way is safe becasue tags isn't needed for freeing such hctx resource.

This approach follows typical design pattern wrt. kobject's release handler.

Cc: Dongli Zhang <dongli.zhang@oracle.com>
Cc: James Smart <james.smart@broadcom.com>
Cc: Bart Van Assche <bart.vanassche@wdc.com>
Cc: linux-scsi@vger.kernel.org,
Cc: Martin K . Petersen <martin.petersen@oracle.com>,
Cc: Christoph Hellwig <hch@lst.de>,
Cc: James E . J . Bottomley <jejb@linux.vnet.ibm.com>,
Reported-by: James Smart <james.smart@broadcom.com>
Fixes: 45a9c9d909b2 ("blk-mq: Fix a use-after-free")
Cc: stable@vger.kernel.org
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: James Smart <james.smart@broadcom.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-core.c     | 2 +-
 block/blk-mq-sysfs.c | 6 ++++++
 block/blk-mq.c       | 8 ++------
 block/blk-mq.h       | 2 +-
 4 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 93dc588fabe2..2dd94b3e9ece 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -374,7 +374,7 @@ void blk_cleanup_queue(struct request_queue *q)
 	blk_exit_queue(q);
 
 	if (queue_is_mq(q))
-		blk_mq_free_queue(q);
+		blk_mq_exit_queue(q);
 
 	percpu_ref_exit(&q->q_usage_counter);
 
diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
index 3f9c3f4ac44c..4040e62c3737 100644
--- a/block/blk-mq-sysfs.c
+++ b/block/blk-mq-sysfs.c
@@ -10,6 +10,7 @@
 #include <linux/smp.h>
 
 #include <linux/blk-mq.h>
+#include "blk.h"
 #include "blk-mq.h"
 #include "blk-mq-tag.h"
 
@@ -33,6 +34,11 @@ static void blk_mq_hw_sysfs_release(struct kobject *kobj)
 {
 	struct blk_mq_hw_ctx *hctx = container_of(kobj, struct blk_mq_hw_ctx,
 						  kobj);
+
+	if (hctx->flags & BLK_MQ_F_BLOCKING)
+		cleanup_srcu_struct(hctx->srcu);
+	blk_free_flush_queue(hctx->fq);
+	sbitmap_free(&hctx->ctx_map);
 	free_cpumask_var(hctx->cpumask);
 	kfree(hctx->ctxs);
 	kfree(hctx);
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 89781309a108..d98cb9614dfa 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2267,12 +2267,7 @@ static void blk_mq_exit_hctx(struct request_queue *q,
 	if (set->ops->exit_hctx)
 		set->ops->exit_hctx(hctx, hctx_idx);
 
-	if (hctx->flags & BLK_MQ_F_BLOCKING)
-		cleanup_srcu_struct(hctx->srcu);
-
 	blk_mq_remove_cpuhp(hctx);
-	blk_free_flush_queue(hctx->fq);
-	sbitmap_free(&hctx->ctx_map);
 }
 
 static void blk_mq_exit_hw_queues(struct request_queue *q,
@@ -2907,7 +2902,8 @@ struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
 }
 EXPORT_SYMBOL(blk_mq_init_allocated_queue);
 
-void blk_mq_free_queue(struct request_queue *q)
+/* tags can _not_ be used after returning from blk_mq_exit_queue */
+void blk_mq_exit_queue(struct request_queue *q)
 {
 	struct blk_mq_tag_set	*set = q->tag_set;
 
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 423ea88ab6fb..633a5a77ee8b 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -37,7 +37,7 @@ struct blk_mq_ctx {
 	struct kobject		kobj;
 } ____cacheline_aligned_in_smp;
 
-void blk_mq_free_queue(struct request_queue *q);
+void blk_mq_exit_queue(struct request_queue *q);
 int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr);
 void blk_mq_wake_waiters(struct request_queue *q);
 bool blk_mq_dispatch_rq_list(struct request_queue *, struct list_head *, bool);
-- 
2.9.5

[PATCH V9 4/7] blk-mq: split blk_mq_alloc_and_init_hctx into two parts

[Ming Lei]

Split blk_mq_alloc_and_init_hctx into two parts, and one is
blk_mq_alloc_hctx() for allocating all hctx resources, another
is blk_mq_init_hctx() for initializing hctx, which serves as
counter-part of blk_mq_exit_hctx().

Cc: Dongli Zhang <dongli.zhang@oracle.com>
Cc: James Smart <james.smart@broadcom.com>
Cc: Bart Van Assche <bart.vanassche@wdc.com>
Cc: linux-scsi@vger.kernel.org
Cc: Martin K . Petersen <martin.petersen@oracle.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: James E . J . Bottomley <jejb@linux.vnet.ibm.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: James Smart <james.smart@broadcom.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-mq.c | 139 +++++++++++++++++++++++++++++++--------------------------
 1 file changed, 75 insertions(+), 64 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index d98cb9614dfa..11efca3534ad 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2284,15 +2284,65 @@ static void blk_mq_exit_hw_queues(struct request_queue *q,
 	}
 }
 
+static int blk_mq_hw_ctx_size(struct blk_mq_tag_set *tag_set)
+{
+	int hw_ctx_size = sizeof(struct blk_mq_hw_ctx);
+
+	BUILD_BUG_ON(ALIGN(offsetof(struct blk_mq_hw_ctx, srcu),
+			   __alignof__(struct blk_mq_hw_ctx)) !=
+		     sizeof(struct blk_mq_hw_ctx));
+
+	if (tag_set->flags & BLK_MQ_F_BLOCKING)
+		hw_ctx_size += sizeof(struct srcu_struct);
+
+	return hw_ctx_size;
+}
+
 static int blk_mq_init_hctx(struct request_queue *q,
 		struct blk_mq_tag_set *set,
 		struct blk_mq_hw_ctx *hctx, unsigned hctx_idx)
 {
-	int node;
+	hctx->queue_num = hctx_idx;
+
+	cpuhp_state_add_instance_nocalls(CPUHP_BLK_MQ_DEAD, &hctx->cpuhp_dead);
+
+	hctx->tags = set->tags[hctx_idx];
+
+	if (set->ops->init_hctx &&
+	    set->ops->init_hctx(hctx, set->driver_data, hctx_idx))
+		goto unregister_cpu_notifier;
 
-	node = hctx->numa_node;
+	if (blk_mq_init_request(set, hctx->fq->flush_rq, hctx_idx,
+				hctx->numa_node))
+		goto exit_hctx;
+	return 0;
+
+ exit_hctx:
+	if (set->ops->exit_hctx)
+		set->ops->exit_hctx(hctx, hctx_idx);
+ unregister_cpu_notifier:
+	blk_mq_remove_cpuhp(hctx);
+	return -1;
+}
+
+static struct blk_mq_hw_ctx *
+blk_mq_alloc_hctx(struct request_queue *q, struct blk_mq_tag_set *set,
+		int node)
+{
+	struct blk_mq_hw_ctx *hctx;
+	gfp_t gfp = GFP_NOIO | __GFP_NOWARN | __GFP_NORETRY;
+
+	hctx = kzalloc_node(blk_mq_hw_ctx_size(set), gfp, node);
+	if (!hctx)
+		goto fail_alloc_hctx;
+
+	if (!zalloc_cpumask_var_node(&hctx->cpumask, gfp, node))
+		goto free_hctx;
+
+	atomic_set(&hctx->nr_active, 0);
 	if (node == NUMA_NO_NODE)
-		node = hctx->numa_node = set->numa_node;
+		node = set->numa_node;
+	hctx->numa_node = node;
 
 	INIT_DELAYED_WORK(&hctx->run_work, blk_mq_run_work_fn);
 	spin_lock_init(&hctx->lock);
@@ -2300,58 +2350,45 @@ static int blk_mq_init_hctx(struct request_queue *q,
 	hctx->queue = q;
 	hctx->flags = set->flags & ~BLK_MQ_F_TAG_SHARED;
 
-	cpuhp_state_add_instance_nocalls(CPUHP_BLK_MQ_DEAD, &hctx->cpuhp_dead);
-
-	hctx->tags = set->tags[hctx_idx];
-
 	/*
 	 * Allocate space for all possible cpus to avoid allocation at
 	 * runtime
 	 */
 	hctx->ctxs = kmalloc_array_node(nr_cpu_ids, sizeof(void *),
-			GFP_NOIO | __GFP_NOWARN | __GFP_NORETRY, node);
+			gfp, node);
 	if (!hctx->ctxs)
-		goto unregister_cpu_notifier;
+		goto free_cpumask;
 
 	if (sbitmap_init_node(&hctx->ctx_map, nr_cpu_ids, ilog2(8),
-				GFP_NOIO | __GFP_NOWARN | __GFP_NORETRY, node))
+				gfp, node))
 		goto free_ctxs;
-
 	hctx->nr_ctx = 0;
 
 	spin_lock_init(&hctx->dispatch_wait_lock);
 	init_waitqueue_func_entry(&hctx->dispatch_wait, blk_mq_dispatch_wake);
 	INIT_LIST_HEAD(&hctx->dispatch_wait.entry);
 
-	if (set->ops->init_hctx &&
-	    set->ops->init_hctx(hctx, set->driver_data, hctx_idx))
-		goto free_bitmap;
-
 	hctx->fq = blk_alloc_flush_queue(q, hctx->numa_node, set->cmd_size,
-			GFP_NOIO | __GFP_NOWARN | __GFP_NORETRY);
+			gfp);
 	if (!hctx->fq)
-		goto exit_hctx;
-
-	if (blk_mq_init_request(set, hctx->fq->flush_rq, hctx_idx, node))
-		goto free_fq;
+		goto free_bitmap;
 
 	if (hctx->flags & BLK_MQ_F_BLOCKING)
 		init_srcu_struct(hctx->srcu);
+	blk_mq_hctx_kobj_init(hctx);
 
-	return 0;
+	return hctx;
 
- free_fq:
-	blk_free_flush_queue(hctx->fq);
- exit_hctx:
-	if (set->ops->exit_hctx)
-		set->ops->exit_hctx(hctx, hctx_idx);
  free_bitmap:
 	sbitmap_free(&hctx->ctx_map);
  free_ctxs:
 	kfree(hctx->ctxs);
- unregister_cpu_notifier:
-	blk_mq_remove_cpuhp(hctx);
-	return -1;
+ free_cpumask:
+	free_cpumask_var(hctx->cpumask);
+ free_hctx:
+	kfree(hctx);
+ fail_alloc_hctx:
+	return NULL;
 }
 
 static void blk_mq_init_cpu_queues(struct request_queue *q,
@@ -2697,51 +2734,25 @@ struct request_queue *blk_mq_init_sq_queue(struct blk_mq_tag_set *set,
 }
 EXPORT_SYMBOL(blk_mq_init_sq_queue);
 
-static int blk_mq_hw_ctx_size(struct blk_mq_tag_set *tag_set)
-{
-	int hw_ctx_size = sizeof(struct blk_mq_hw_ctx);
-
-	BUILD_BUG_ON(ALIGN(offsetof(struct blk_mq_hw_ctx, srcu),
-			   __alignof__(struct blk_mq_hw_ctx)) !=
-		     sizeof(struct blk_mq_hw_ctx));
-
-	if (tag_set->flags & BLK_MQ_F_BLOCKING)
-		hw_ctx_size += sizeof(struct srcu_struct);
-
-	return hw_ctx_size;
-}
-
 static struct blk_mq_hw_ctx *blk_mq_alloc_and_init_hctx(
 		struct blk_mq_tag_set *set, struct request_queue *q,
 		int hctx_idx, int node)
 {
 	struct blk_mq_hw_ctx *hctx;
 
-	hctx = kzalloc_node(blk_mq_hw_ctx_size(set),
-			GFP_NOIO | __GFP_NOWARN | __GFP_NORETRY,
-			node);
+	hctx = blk_mq_alloc_hctx(q, set, node);
 	if (!hctx)
-		return NULL;
-
-	if (!zalloc_cpumask_var_node(&hctx->cpumask,
-				GFP_NOIO | __GFP_NOWARN | __GFP_NORETRY,
-				node)) {
-		kfree(hctx);
-		return NULL;
-	}
-
-	atomic_set(&hctx->nr_active, 0);
-	hctx->numa_node = node;
-	hctx->queue_num = hctx_idx;
+		goto fail;
 
-	if (blk_mq_init_hctx(q, set, hctx, hctx_idx)) {
-		free_cpumask_var(hctx->cpumask);
-		kfree(hctx);
-		return NULL;
-	}
-	blk_mq_hctx_kobj_init(hctx);
+	if (blk_mq_init_hctx(q, set, hctx, hctx_idx))
+		goto free_hctx;
 
 	return hctx;
+
+ free_hctx:
+	kobject_put(&hctx->kobj);
+ fail:
+	return NULL;
 }
 
 static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
-- 
2.9.5

[PATCH V9 5/7] blk-mq: always free hctx after request queue is freed

[Ming Lei]

In normal queue cleanup path, hctx is released after request queue
is freed, see blk_mq_release().

However, in __blk_mq_update_nr_hw_queues(), hctx may be freed because
of hw queues shrinking. This way is easy to cause use-after-free,
because: one implicit rule is that it is safe to call almost all block
layer APIs if the request queue is alive; and one hctx may be retrieved
by one API, then the hctx can be freed by blk_mq_update_nr_hw_queues();
finally use-after-free is triggered.

Fixes this issue by always freeing hctx after releasing request queue.
If some hctxs are removed in blk_mq_update_nr_hw_queues(), introduce
a per-queue list to hold them, then try to resuse these hctxs if numa
node is matched.

Cc: Dongli Zhang <dongli.zhang@oracle.com>
Cc: James Smart <james.smart@broadcom.com>
Cc: Bart Van Assche <bart.vanassche@wdc.com>
Cc: linux-scsi@vger.kernel.org,
Cc: Martin K . Petersen <martin.petersen@oracle.com>,
Cc: Christoph Hellwig <hch@lst.de>,
Cc: James E . J . Bottomley <jejb@linux.vnet.ibm.com>,
Reviewed-by: Hannes Reinecke <hare@suse.com>
Tested-by: James Smart <james.smart@broadcom.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-mq.c         | 46 +++++++++++++++++++++++++++++++++-------------
 include/linux/blk-mq.h |  2 ++
 include/linux/blkdev.h |  7 +++++++
 3 files changed, 42 insertions(+), 13 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 11efca3534ad..e6cee57a5bf0 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2268,6 +2268,10 @@ static void blk_mq_exit_hctx(struct request_queue *q,
 		set->ops->exit_hctx(hctx, hctx_idx);
 
 	blk_mq_remove_cpuhp(hctx);
+
+	spin_lock(&q->unused_hctx_lock);
+	list_add(&hctx->hctx_list, &q->unused_hctx_list);
+	spin_unlock(&q->unused_hctx_lock);
 }
 
 static void blk_mq_exit_hw_queues(struct request_queue *q,
@@ -2350,6 +2354,8 @@ blk_mq_alloc_hctx(struct request_queue *q, struct blk_mq_tag_set *set,
 	hctx->queue = q;
 	hctx->flags = set->flags & ~BLK_MQ_F_TAG_SHARED;
 
+	INIT_LIST_HEAD(&hctx->hctx_list);
+
 	/*
 	 * Allocate space for all possible cpus to avoid allocation at
 	 * runtime
@@ -2663,15 +2669,17 @@ static int blk_mq_alloc_ctxs(struct request_queue *q)
  */
 void blk_mq_release(struct request_queue *q)
 {
-	struct blk_mq_hw_ctx *hctx;
-	unsigned int i;
+	struct blk_mq_hw_ctx *hctx, *next;
+	int i;
 
 	cancel_delayed_work_sync(&q->requeue_work);
 
-	/* hctx kobj stays in hctx */
-	queue_for_each_hw_ctx(q, hctx, i) {
-		if (!hctx)
-			continue;
+	queue_for_each_hw_ctx(q, hctx, i)
+		WARN_ON_ONCE(hctx && list_empty(&hctx->hctx_list));
+
+	/* all hctx are in .unused_hctx_list now */
+	list_for_each_entry_safe(hctx, next, &q->unused_hctx_list, hctx_list) {
+		list_del_init(&hctx->hctx_list);
 		kobject_put(&hctx->kobj);
 	}
 
@@ -2738,9 +2746,22 @@ static struct blk_mq_hw_ctx *blk_mq_alloc_and_init_hctx(
 		struct blk_mq_tag_set *set, struct request_queue *q,
 		int hctx_idx, int node)
 {
-	struct blk_mq_hw_ctx *hctx;
+	struct blk_mq_hw_ctx *hctx = NULL, *tmp;
 
-	hctx = blk_mq_alloc_hctx(q, set, node);
+	/* reuse dead hctx first */
+	spin_lock(&q->unused_hctx_lock);
+	list_for_each_entry(tmp, &q->unused_hctx_list, hctx_list) {
+		if (tmp->numa_node == node) {
+			hctx = tmp;
+			break;
+		}
+	}
+	if (hctx)
+		list_del_init(&hctx->hctx_list);
+	spin_unlock(&q->unused_hctx_lock);
+
+	if (!hctx)
+		hctx = blk_mq_alloc_hctx(q, set, node);
 	if (!hctx)
 		goto fail;
 
@@ -2778,10 +2799,8 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
 
 		hctx = blk_mq_alloc_and_init_hctx(set, q, i, node);
 		if (hctx) {
-			if (hctxs[i]) {
+			if (hctxs[i])
 				blk_mq_exit_hctx(q, set, hctxs[i], i);
-				kobject_put(&hctxs[i]->kobj);
-			}
 			hctxs[i] = hctx;
 		} else {
 			if (hctxs[i])
@@ -2812,9 +2831,7 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
 			if (hctx->tags)
 				blk_mq_free_map_and_requests(set, j);
 			blk_mq_exit_hctx(q, set, hctx, j);
-			kobject_put(&hctx->kobj);
 			hctxs[j] = NULL;
-
 		}
 	}
 	mutex_unlock(&q->sysfs_lock);
@@ -2857,6 +2874,9 @@ struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
 	if (!q->queue_hw_ctx)
 		goto err_sys_init;
 
+	INIT_LIST_HEAD(&q->unused_hctx_list);
+	spin_lock_init(&q->unused_hctx_lock);
+
 	blk_mq_realloc_hw_ctxs(set, q);
 	if (!q->nr_hw_queues)
 		goto err_hctxs;
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index db29928de467..15d1aa53d96c 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -70,6 +70,8 @@ struct blk_mq_hw_ctx {
 	struct dentry		*sched_debugfs_dir;
 #endif
 
+	struct list_head	hctx_list;
+
 	/* Must be the last member - see also blk_mq_hw_ctx_size(). */
 	struct srcu_struct	srcu[0];
 };
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 99aa98f60b9e..d7bad4ae8bc8 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -535,6 +535,13 @@ struct request_queue {
 
 	struct mutex		sysfs_lock;
 
+	/*
+	 * for reusing dead hctx instance in case of updating
+	 * nr_hw_queues
+	 */
+	struct list_head	unused_hctx_list;
+	spinlock_t		unused_hctx_lock;
+
 	atomic_t		mq_freeze_depth;
 
 #if defined(CONFIG_BLK_DEV_BSG)
-- 
2.9.5

[PATCH V9 6/7] blk-mq: move cancel of hctx->run_work into blk_mq_hw_sysfs_release

[Ming Lei]

hctx is always released after requeue is freed.

With holding queue's kobject refcount, it is safe for driver to run queue,
so one run queue might be scheduled after blk_sync_queue() is done.

So moving the cancel of hctx->run_work into blk_mq_hw_sysfs_release()
for avoiding run released queue.

Cc: Dongli Zhang <dongli.zhang@oracle.com>
Cc: James Smart <james.smart@broadcom.com>
Cc: Bart Van Assche <bart.vanassche@wdc.com>
Cc: linux-scsi@vger.kernel.org,
Cc: Martin K . Petersen <martin.petersen@oracle.com>,
Cc: Christoph Hellwig <hch@lst.de>,
Cc: James E . J . Bottomley <jejb@linux.vnet.ibm.com>,
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Tested-by: James Smart <james.smart@broadcom.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-core.c     | 8 --------
 block/blk-mq-sysfs.c | 2 ++
 2 files changed, 2 insertions(+), 8 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 2dd94b3e9ece..f5b5f21ae4fd 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -232,14 +232,6 @@ void blk_sync_queue(struct request_queue *q)
 {
 	del_timer_sync(&q->timeout);
 	cancel_work_sync(&q->timeout_work);
-
-	if (queue_is_mq(q)) {
-		struct blk_mq_hw_ctx *hctx;
-		int i;
-
-		queue_for_each_hw_ctx(q, hctx, i)
-			cancel_delayed_work_sync(&hctx->run_work);
-	}
 }
 EXPORT_SYMBOL(blk_sync_queue);
 
diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
index 4040e62c3737..25c0d0a6a556 100644
--- a/block/blk-mq-sysfs.c
+++ b/block/blk-mq-sysfs.c
@@ -35,6 +35,8 @@ static void blk_mq_hw_sysfs_release(struct kobject *kobj)
 	struct blk_mq_hw_ctx *hctx = container_of(kobj, struct blk_mq_hw_ctx,
 						  kobj);
 
+	cancel_delayed_work_sync(&hctx->run_work);
+
 	if (hctx->flags & BLK_MQ_F_BLOCKING)
 		cleanup_srcu_struct(hctx->srcu);
 	blk_free_flush_queue(hctx->fq);
-- 
2.9.5

[PATCH V9 7/7] block: don't drain in-progress dispatch in blk_cleanup_queue()

[Ming Lei]

Now freeing hw queue resource is moved to hctx's release handler,
we don't need to worry about the race between blk_cleanup_queue and
run queue any more.

So don't drain in-progress dispatch in blk_cleanup_queue().

This is basically revert of c2856ae2f315 ("blk-mq: quiesce queue before
freeing queue").

Cc: Dongli Zhang <dongli.zhang@oracle.com>
Cc: James Smart <james.smart@broadcom.com>
Cc: Bart Van Assche <bart.vanassche@wdc.com>
Cc: linux-scsi@vger.kernel.org,
Cc: Martin K . Petersen <martin.petersen@oracle.com>,
Cc: Christoph Hellwig <hch@lst.de>,
Cc: James E . J . Bottomley <jejb@linux.vnet.ibm.com>,
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Tested-by: James Smart <james.smart@broadcom.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-core.c | 12 ------------
 1 file changed, 12 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index f5b5f21ae4fd..e24cfcefdc19 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -338,18 +338,6 @@ void blk_cleanup_queue(struct request_queue *q)
 
 	blk_queue_flag_set(QUEUE_FLAG_DEAD, q);
 
-	/*
-	 * make sure all in-progress dispatch are completed because
-	 * blk_freeze_queue() can only complete all requests, and
-	 * dispatch may still be in-progress since we dispatch requests
-	 * from more than one contexts.
-	 *
-	 * We rely on driver to deal with the race in case that queue
-	 * initialization isn't done.
-	 */
-	if (queue_is_mq(q) && blk_queue_init_done(q))
-		blk_mq_quiesce_queue(q);
-
 	/* for synchronous bio-based driver finish in-flight integrity i/o */
 	blk_flush_integrity();
 
-- 
2.9.5

Re: [PATCH V9 1/7] blk-mq: grab .q_usage_counter when queuing request from plug code path

[Bart Van Assche]

On 4/29/19 6:52 PM, Ming Lei wrote:
> Just like aio/io_uring, we need to grab 2 refcount for queuing one
> request, one is for submission, another is for completion.
> 
> If the request isn't queued from plug code path, the refcount grabbed
> in generic_make_request() serves for submission. In theroy, this
> refcount should have been released after the sumission(async run queue)
> is done. blk_freeze_queue() works with blk_sync_queue() together
> for avoiding race between cleanup queue and IO submission, given async
> run queue activities are canceled because hctx->run_work is scheduled with
> the refcount held, so it is fine to not hold the refcount when
> running the run queue work function for dispatch IO.
> 
> However, if request is staggered into plug list, and finally queued
> from plug code path, the refcount in submission side is actually missed.
> And we may start to run queue after queue is removed because the queue's
> kobject refcount isn't guaranteed to be grabbed in flushing plug list
> context, then kernel oops is triggered, see the following race:
> 
> blk_mq_flush_plug_list():
>         blk_mq_sched_insert_requests()
>                 insert requests to sw queue or scheduler queue
>                 blk_mq_run_hw_queue
> 
> Because of concurrent run queue, all requests inserted above may be
> completed before calling the above blk_mq_run_hw_queue. Then queue can
> be freed during the above blk_mq_run_hw_queue().
> 
> Fixes the issue by grab .q_usage_counter before calling
> blk_mq_sched_insert_requests() in blk_mq_flush_plug_list(). This way is
> safe because the queue is absolutely alive before inserting request.

Reviewed-by: Bart Van Assche <bvanassche@acm.org>

Re: [PATCH V9 0/7] blk-mq: fix races related with freeing queue

[Jens Axboe]

On 4/29/19 7:52 PM, Ming Lei wrote:
> Hi,
> 
> Since 45a9c9d909b2 ("blk-mq: Fix a use-after-free"), run queue isn't
> allowed during cleanup queue even though queue refcount is held.
> 
> This change has caused lots of kernel oops triggered in run queue path,
> turns out it isn't easy to fix them all.
> 
> So move freeing of hw queue resources into hctx's release handler, then
> the above issue is fixed. Meantime, this way is safe given freeing hw
> queue resource doesn't require tags.

Applied, thanks Ming.

-- 
Jens Axboe