linux-kernel - [PATCH] tty/hvc_console: fix console lock ordering with spinlock

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Message-Id: <1490882779-16066-1-git-send-email-kda@linux-powerpc.org>
Date:   Thu, 30 Mar 2017 10:06:19 -0400
From:   Denis Kirjanov <kda@...ux-powerpc.org>
To:     gregkh@...uxfoundation.org, jslaby@...e.com
Cc:     linuxppc-dev@...abs.org, linux-kernel@...r.kernel.org,
        benh@...nel.crashing.org, Denis Kirjanov <kda@...ux-powerpc.org>
Subject: [PATCH] tty/hvc_console: fix console lock ordering with spinlock

hvc_remove() takes a spin lock first then acquires the console
semaphore. This situation can easily lead to a deadlock scenario
where we call scheduler with spin lock held.

Signed-off-by: Denis Kirjanov <kda@...ux-powerpc.org>
---
 drivers/tty/hvc/hvc_console.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
index b19ae36..a8d3991 100644
--- a/drivers/tty/hvc/hvc_console.c
+++ b/drivers/tty/hvc/hvc_console.c
@@ -920,17 +920,17 @@ int hvc_remove(struct hvc_struct *hp)
 
 	tty = tty_port_tty_get(&hp->port);
 
+	console_lock();
 	spin_lock_irqsave(&hp->lock, flags);
 	if (hp->index < MAX_NR_HVC_CONSOLES) {
-		console_lock();
 		vtermnos[hp->index] = -1;
 		cons_ops[hp->index] = NULL;
-		console_unlock();
 	}
 
 	/* Don't whack hp->irq because tty_hangup() will need to free the irq. */
 
 	spin_unlock_irqrestore(&hp->lock, flags);
+	console_unlock();
 
 	/*
 	 * We 'put' the instance that was grabbed when the kref instance
-- 
1.8.3.1