race condition between shutdown() and post_reset() resulting in deadlock

[Oliver Neukum <oneukum@suse.com>]

Hi,

looking at your last patch I noticed something.
I think it fails to work if we hit a peculiar race condition.
It looks to me like we can get the following:

task A

pre_reset()
  --> calling scsi_block_requests()

					task B

					shutdown()
					  --> setting the shutdown flag


post_reset()
  --> checking the flag -> do nothing -> deadlock

So we need in addition something like the below patch.
What do you think?

	Regards
		Oliver

From 68cc8940d7dde8e2a48217d8086cd692809e7980 Mon Sep 17 00:00:00 2001
From: Oliver Neukum <oneukum@suse.com>
Date: Mon, 15 Jan 2018 13:56:59 +0100
Subject: [PATCH] UAS: fix race between post_reset() and shutdown()

Disconnect due to shutdown can happen after pre_reset() has been called. Thus the host
must be unblocked even in the shutdown case.

Signed-off-by: Oliver Neukum <oneukum@suse.com>
---
 drivers/usb/storage/uas.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/storage/uas.c b/drivers/usb/storage/uas.c
index 338133a239df..d5ed1e581fb5 100644
--- a/drivers/usb/storage/uas.c
+++ b/drivers/usb/storage/uas.c
@@ -1046,10 +1046,11 @@ static int uas_post_reset(struct usb_interface *intf)
 	struct Scsi_Host *shost = usb_get_intfdata(intf);
 	struct uas_dev_info *devinfo = (struct uas_dev_info *)shost->hostdata;
 	unsigned long flags;
-	int err;
+	int err = 1;
 
+	/* We may have lost the race and shutdown after pre_reset() */
 	if (devinfo->shutdown)
-		return 0;
+		goto skip;
 
 	err = uas_configure_endpoints(devinfo);
 	if (err && err != ENODEV)
@@ -1062,6 +1063,7 @@ static int uas_post_reset(struct usb_interface *intf)
 	scsi_report_bus_reset(shost, 0);
 	spin_unlock_irqrestore(shost->host_lock, flags);
 
+skip:
 	scsi_unblock_requests(shost);
 
 	return err ? 1 : 0;