patch "xhci: Prevent deadlock when xhci adapter breaks during init" added to usb-linus

This is a note to let you know that I've just added the patch titled

xhci: Prevent deadlock when xhci adapter breaks during init

to my usb git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From 8de66b0e6a56ff10dd00d2b0f2ae52e300178587 Mon Sep 17 00:00:00 2001
From: Bill Kuzeja <[email protected]>
Date: Fri, 4 Oct 2019 14:59:31 +0300
Subject: xhci: Prevent deadlock when xhci adapter breaks during init

The system can hit a deadlock if an xhci adapter breaks while initializing. The deadlock is between two threads: thread 1 is tearing down the adapter and is stuck in usb_unlocked_disable_lpm waiting to lock the hcd->handwidth_mutex. Thread 2 is holding this mutex (while still trying to add a usb device), but is stuck in xhci_endpoint_reset waiting for a stop or config command to complete. A reboot is required to resolve.

It turns out when calling xhci_queue_stop_endpoint and xhci_queue_configure_endpoint in xhci_endpoint_reset, the return code is not checked for errors. If the timing is right and the adapter dies just before either of these commands get issued, we hang indefinitely waiting for a completion on a command that didn't get issued.

This wasn't a problem before the following fix because we didn't send commands in xhci_endpoint_reset:

commit f5249461b504 ("xhci: Clear the host side toggle manually when
endpoint is soft reset")

With the patch I am submitting, a duration test which breaks adapters during initialization (and which deadlocks with the standard kernel) runs without issue.

---
 drivers/usb/host/xhci.c | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

index fe8f9ff58015..8c068d0cc7c1 100644
@@ -3095,6 +3095,7 @@ static void xhci_endpoint_reset(struct usb_hcd *hcd,
 	unsigned int ep_index;
 	unsigned long flags;
 	u32 ep_flag;
+	int err;
 
 	xhci = hcd_to_xhci(hcd);
 	if (!host_ep->hcpriv)

@@ -3154,7 +3155,17 @@ static void xhci_endpoint_reset(struct usb_hcd *hcd,
 		xhci_free_command(xhci, cfg_cmd);
 		goto cleanup;
 	}
-	xhci_queue_stop_endpoint(xhci, stop_cmd, udev->slot_id, ep_index, 0);
+
+	err = xhci_queue_stop_endpoint(xhci, stop_cmd, udev->slot_id,
+					ep_index, 0);
+	if (err < 0) {
+		spin_unlock_irqrestore(&xhci->lock, flags);
+		xhci_free_command(xhci, cfg_cmd);
+		xhci_dbg(xhci, "%s: Failed to queue stop ep command, %d ",
+				__func__, err);
+		goto cleanup;
+	}
+
 	xhci_ring_cmd_db(xhci);
 	spin_unlock_irqrestore(&xhci->lock, flags);
 

@@ -3168,8 +3179,16 @@ static void xhci_endpoint_reset(struct usb_hcd *hcd,
 					   ctrl_ctx, ep_flag, ep_flag);
 	xhci_endpoint_copy(xhci, cfg_cmd->in_ctx, vdev->out_ctx, ep_index);
 
-	xhci_queue_configure_endpoint(xhci, cfg_cmd, cfg_cmd->in_ctx->dma,
+	err = xhci_queue_configure_endpoint(xhci, cfg_cmd, cfg_cmd->in_ctx->dma,
 				      udev->slot_id, false);
+	if (err < 0) {
+		spin_unlock_irqrestore(&xhci->lock, flags);
+		xhci_free_command(xhci, cfg_cmd);
+		xhci_dbg(xhci, "%s: Failed to queue config ep command, %d ",
+				__func__, err);
+		goto cleanup;
+	}
+
 	xhci_ring_cmd_db(xhci);
 	spin_unlock_irqrestore(&xhci->lock, flags);
 

2.23.0