linux-kernel - [PATCH] 9p/xen: fix init sequence

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Message-ID: <20241119211633.38321-1-alexander@edera.dev>
Date: Tue, 19 Nov 2024 21:16:33 +0000
From: Alexander Merritt <alexander@...ra.dev>
To: v9fs@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	xen-devel@...ts.xenproject.org
Cc: Eric Van Hensbergen <ericvh@...nel.org>,
	Latchesar Ionkov <lucho@...kov.net>,
	Dominique Martinet <asmadeus@...ewreck.org>,
	Christian Schoenebeck <linux_oss@...debyte.com>,
	Simon Horman <horms@...nel.org>,
	Juergen Gross <jgross@...e.com>,
	Alex Zenla <alex@...ra.dev>,
	Alexander Merritt <alexander@...ra.dev>,
	Ariadne Conill <ariadne@...adne.space>
Subject: [PATCH] 9p/xen: fix init sequence

From: Alex Zenla <alex@...ra.dev>

Large amount of mount hangs observed during hotplugging of 9pfs devices. The
9pfs Xen driver attempts to initialize itself more than once, causing the
frontend and backend to disagree: the backend listens on a channel that the
frontend does not send on, resulting in stalled processing.

Only allow initialization of 9p frontend once.

Fixes: c15fe55d14b3b ("9p/xen: fix connection sequence")
Signed-off-by: Alex Zenla <alex@...ra.dev>
Signed-off-by: Alexander Merritt <alexander@...ra.dev>
Signed-off-by: Ariadne Conill <ariadne@...adne.space>
---
 net/9p/trans_xen.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/9p/trans_xen.c b/net/9p/trans_xen.c
index dfdbe1ca5338..0304e8a1616d 100644
--- a/net/9p/trans_xen.c
+++ b/net/9p/trans_xen.c
@@ -465,6 +465,7 @@ static int xen_9pfs_front_init(struct xenbus_device *dev)
 		goto error;
 	}
 
+	xenbus_switch_state(dev, XenbusStateInitialised);
 	return 0;
 
  error_xenbus:
@@ -512,8 +513,10 @@ static void xen_9pfs_front_changed(struct xenbus_device *dev,
 		break;
 
 	case XenbusStateInitWait:
-		if (!xen_9pfs_front_init(dev))
-			xenbus_switch_state(dev, XenbusStateInitialised);
+		if (dev->state != XenbusStateInitialising)
+			break;
+
+		xen_9pfs_front_init(dev);
 		break;
 
 	case XenbusStateConnected:
-- 
2.43.0