[PATCH v4] nvme/host/pci: Fix a race in controller removal

[PATCH v4] nvme/host/pci: Fix a race in controller removal

[Balbir Singh]

User space programs like udevd may try to read to partitions at the
same time the driver detects a namespace is unusable, and may deadlock
if revalidate_disk() is called while such a process is waiting to
enter the frozen queue. On detecting a dead namespace, move the disk
revalidate after unblocking dispatchers that may be holding bd_butex.

changelog Suggested-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Balbir Singh <sblbir@amzn.com>
---
Changelov v4
 - Simplify the changelog
Changelog v3
 - Simplify the comment about moving revalidate_disk
Changelog v2
 - Rely on blk_set_queue_dying to do the wake_all()

 drivers/nvme/host/core.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index b45f82d58be8..6ad1f1df9e44 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -103,10 +103,13 @@ static void nvme_set_queue_dying(struct nvme_ns *ns)
 	 */
 	if (!ns->disk || test_and_set_bit(NVME_NS_DEAD, &ns->flags))
 		return;
-	revalidate_disk(ns->disk);
 	blk_set_queue_dying(ns->queue);
 	/* Forcibly unquiesce queues to avoid blocking dispatch */
 	blk_mq_unquiesce_queue(ns->queue);
+	/*
+	 * Revalidate after unblocking dispatchers that may be holding bd_butex
+	 */
+	revalidate_disk(ns->disk);
 }
 
 static void nvme_queue_scan(struct nvme_ctrl *ctrl)
-- 
2.16.5


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Re: [PATCH v4] nvme/host/pci: Fix a race in controller removal

[Keith Busch]

On Wed, Sep 18, 2019 at 12:27:20AM +0000, Balbir Singh wrote:
> User space programs like udevd may try to read to partitions at the
> same time the driver detects a namespace is unusable, and may deadlock
> if revalidate_disk() is called while such a process is waiting to
> enter the frozen queue. On detecting a dead namespace, move the disk
> revalidate after unblocking dispatchers that may be holding bd_butex.

Patch looks fine.

Reviewed-by: Keith Busch <kbusch@kernel.org>

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