linux-kernel - [PATCH 4/4] isicom: fix deadlock on shutdown

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Message-ID: <20091007144643.14550.7683.stgit@localhost.localdomain>
Date:	Wed, 07 Oct 2009 15:46:50 +0100
From:	Alan Cox <alan@...ux.intel.com>
To:	linux-kernel@...r.kernel.org, strakh@...ras.ru, jirislaby@...il.com
Subject: [PATCH 4/4] isicom: fix deadlock on shutdown

Alexander Strakh <strakh@...ras.ru> reported

	KERNEL_VERSION: 2.6.31
	DESCRIBE:
Driver drivers/char/isicom.c might sleep in atomic  context, because it
calls 
tty_port_xmit_buf under spin_lock.

./drivers/char/isicom.c:
1307 static void isicom_hangup(struct tty_struct *tty)
1308 {
...
1315         spin_lock_irqsave(&port->card->card_lock, flags);
1316         isicom_shutdown_port(port);
...

Path to might_sleep macro from isicom_hangup:
1. isicom_hangup calls spin_lock_irqsave (drivers/char/isicom.c:1315) and
then 
calls isicom_shutdown_port.
2. isiscom_shutdown_port calls tty_port_free_xmit_buf at 
drivers/char/isicom.c:906
3. tty_port_free_xmit_buf calls mutex_lock at drivers/char/tty_port:48

Found by Linux Driver Verification Project.

Signed-off-by: Alan Cox <alan@...ux.intel.com>
---

 drivers/char/isicom.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)


diff --git a/drivers/char/isicom.c b/drivers/char/isicom.c
index 1e91c30..300d5bd 100644
--- a/drivers/char/isicom.c
+++ b/drivers/char/isicom.c
@@ -887,7 +887,6 @@ static void isicom_shutdown_port(struct isi_port *port)
 {
 	struct isi_board *card = port->card;
 
-	tty_port_free_xmit_buf(&port->port);
 	if (--card->count < 0) {
 		pr_dbg("isicom_shutdown_port: bad board(0x%lx) count %d.\n",
 			card->base, card->count);
@@ -927,6 +926,7 @@ static void isicom_shutdown(struct tty_port *port)
 	outw(card->port_status, card->base + 0x02);
 	isicom_shutdown_port(ip);
 	spin_unlock_irqrestore(&card->card_lock, flags);
+	tty_port_free_xmit_buf(port);
 }
 
 static void isicom_close(struct tty_struct *tty, struct file *filp)

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