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From: Willy Tarreau <w@1wt.eu>
To: linux-kernel@vger.kernel.org, stable@kernel.org,
	stable-review@kernel.org
Cc: Amit Shah <amit.shah@redhat.com>,
	Alan Cox <alan@lxorguk.ukuu.org.uk>,
	linuxppc-dev@ozlabs.org, Rusty Russell <rusty@rustcorp.com.au>,
	Greg Kroah-Hartman <gregkh@suse.de>, Willy Tarreau <w@1wt.eu>
Subject: [PATCH 21/23] hvc_console: Fix race between hvc_close and hvc_remove
Date: Mon, 07 Feb 2011 00:23:13 +0100	[thread overview]
Message-ID: <20110206232253.421321729@pcw.home.local> (raw)
In-Reply-To: <4beed4da27f06efb2c13d6ed48850634@local>

2.6.27.58-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Amit Shah <amit.shah@redhat.com>

commit e74d098c66543d0731de62eb747ccd5b636a6f4c upstream.

Alan pointed out a race in the code where hvc_remove is invoked. The
recent virtio_console work is the first user of hvc_remove().

Alan describes it thus:

The hvc_console assumes that a close and remove call can't occur at the
same time.

In addition tty_hangup(tty) is problematic as tty_hangup is asynchronous
itself....

So this can happen

        hvc_close                               hvc_remove
        hung up ? - no
                                                lock
                                                tty = hp->tty
                                                unlock
        lock
        hp->tty = NULL
        unlock
        notify del
        kref_put the hvc struct
        close completes
        tty is destroyed
                                                tty_hangup dead tty
                                                tty->ops will be NULL
                                                NULL->...

This patch adds some tty krefs and also converts to using tty_vhangup().

Reported-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
CC: Alan Cox <alan@lxorguk.ukuu.org.uk>
CC: linuxppc-dev@ozlabs.org
CC: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Willy Tarreau <w@1wt.eu>

---
 drivers/char/hvc_console.c |   31 +++++++++++++++++++++----------
 1 file changed, 21 insertions(+), 10 deletions(-)

Index: longterm-2.6.27/drivers/char/hvc_console.c
===================================================================
--- longterm-2.6.27.orig/drivers/char/hvc_console.c	2011-01-23 10:52:15.000000000 +0100
+++ longterm-2.6.27/drivers/char/hvc_console.c	2011-01-29 15:33:05.169065818 +0100
@@ -312,6 +312,7 @@
 	spin_lock_irqsave(&hp->lock, flags);
 	/* Check and then increment for fast path open. */
 	if (hp->count++ > 0) {
+		tty_kref_get(tty);
 		spin_unlock_irqrestore(&hp->lock, flags);
 		hvc_kick();
 		return 0;
@@ -320,7 +321,7 @@
 	tty->driver_data = hp;
 	tty->low_latency = 1; /* Makes flushes to ldisc synchronous. */
 
-	hp->tty = tty;
+	hp->tty = tty_kref_get(tty);
 
 	spin_unlock_irqrestore(&hp->lock, flags);
 
@@ -337,6 +338,7 @@
 		spin_lock_irqsave(&hp->lock, flags);
 		hp->tty = NULL;
 		spin_unlock_irqrestore(&hp->lock, flags);
+		tty_kref_put(tty);
 		tty->driver_data = NULL;
 		kref_put(&hp->kref, destroy_hvc_struct);
 		printk(KERN_ERR "hvc_open: request_irq failed with rc %d.\n", rc);
@@ -364,13 +366,18 @@
 		return;
 
 	hp = tty->driver_data;
+
 	spin_lock_irqsave(&hp->lock, flags);
+	tty_kref_get(tty);
 
 	if (--hp->count == 0) {
 		/* We are done with the tty pointer now. */
 		hp->tty = NULL;
 		spin_unlock_irqrestore(&hp->lock, flags);
 
+		/* Put the ref obtained in hvc_open() */
+		tty_kref_put(tty);
+
 		if (hp->ops->notifier_del)
 			hp->ops->notifier_del(hp, hp->data);
 
@@ -387,6 +394,7 @@
 		spin_unlock_irqrestore(&hp->lock, flags);
 	}
 
+	tty_kref_put(tty);
 	kref_put(&hp->kref, destroy_hvc_struct);
 }
 
@@ -423,6 +431,7 @@
 
 	while(temp_open_count) {
 		--temp_open_count;
+		tty_kref_put(tty);
 		kref_put(&hp->kref, destroy_hvc_struct);
 	}
 }
@@ -550,7 +559,7 @@
 		poll_mask |= HVC_POLL_WRITE;
 
 	/* No tty attached, just skip */
-	tty = hp->tty;
+	tty = tty_kref_get(hp->tty);
 	if (tty == NULL)
 		goto bail;
 
@@ -627,6 +636,8 @@
 
 		tty_flip_buffer_push(tty);
 	}
+	if (tty)
+		tty_kref_put(tty);
 
 	return poll_mask;
 }
@@ -749,7 +760,7 @@
 	struct tty_struct *tty;
 
 	spin_lock_irqsave(&hp->lock, flags);
-	tty = hp->tty;
+	tty = tty_kref_get(hp->tty);
 
 	if (hp->index < MAX_NR_HVC_CONSOLES)
 		vtermnos[hp->index] = -1;
@@ -761,18 +772,18 @@
 	/*
 	 * We 'put' the instance that was grabbed when the kref instance
 	 * was initialized using kref_init().  Let the last holder of this
-	 * kref cause it to be removed, which will probably be the tty_hangup
+	 * kref cause it to be removed, which will probably be the tty_vhangup
 	 * below.
 	 */
 	kref_put(&hp->kref, destroy_hvc_struct);
 
 	/*
-	 * This function call will auto chain call hvc_hangup.  The tty should
-	 * always be valid at this time unless a simultaneous tty close already
-	 * cleaned up the hvc_struct.
+	 * This function call will auto chain call hvc_hangup.
 	 */
-	if (tty)
-		tty_hangup(tty);
+	if (tty) {
+		tty_vhangup(tty);
+		tty_kref_put(tty);
+	}
 	return 0;
 }
 



  parent reply	other threads:[~2011-02-06 23:45 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20110206232252.509080428@pcw.home.local>
2011-02-06 23:22 ` [PATCH 00/23] 2.6.27.58-longterm review Willy Tarreau
2011-02-06 23:22   ` [PATCH 01/23] ALSA: hda: Use model=lg quirk for LG P1 Express to enable playback and capture Willy Tarreau
2011-02-06 23:22   ` [PATCH 02/23] ALSA: hda: Use LPIB for Dell Latitude 131L Willy Tarreau
2011-02-06 23:22   ` [PATCH 03/23] ALSA: hda: Use LPIB quirk for Dell Inspiron m101z/1120 Willy Tarreau
2011-02-06 23:22   ` [PATCH 04/23] USB: usb-storage: unusual_devs entry for the Samsung YP-CP3 Willy Tarreau
2011-02-06 23:22   ` [PATCH 05/23] USB: misc: uss720.c: add another vendor/product ID Willy Tarreau
2011-02-06 23:22   ` [PATCH 06/23] HID: hidraw: fix window in hidraw_release Willy Tarreau
2011-02-06 23:22   ` [PATCH 07/23] hwmon: (adm1026) Allow 1 as a valid divider value Willy Tarreau
2011-02-06 23:23   ` [PATCH 08/23] hwmon: (adm1026) Fix setting fan_div Willy Tarreau
2011-02-06 23:23   ` [PATCH 09/23] IB/uverbs: Handle large number of entries in poll CQ Willy Tarreau
2011-02-06 23:23   ` [PATCH 10/23] mv_xor: fix race in tasklet function Willy Tarreau
2011-02-06 23:23   ` [PATCH 11/23] md: fix bug with re-adding of partially recovered device Willy Tarreau
2011-02-06 23:23   ` [PATCH 12/23] NFS: Fix fcntl F_GETLK not reporting some conflicts Willy Tarreau
2011-02-06 23:23   ` [PATCH 13/23] nfsd: Fix possible BUG_ON firing in set_change_info Willy Tarreau
2011-02-06 23:23   ` [PATCH 14/23] PM / Hibernate: Fix PM_POST_* notification with user-space suspend Willy Tarreau
2011-02-06 23:23   ` [PATCH 15/23] posix-cpu-timers: workaround to suppress the problems with mt exec Willy Tarreau
2011-02-06 23:23   ` [PATCH 16/23] sctp: Fix a race between ICMP protocol unreachable and connect() Willy Tarreau
2011-02-06 23:23   ` [PATCH 17/23] sound: Prevent buffer overflow in OSS load_mixer_volumes Willy Tarreau
2011-02-06 23:23   ` [PATCH 18/23] sunrpc: prevent use-after-free on clearing XPT_BUSY Willy Tarreau
2011-02-06 23:23   ` [PATCH 19/23] x86, gcc-4.6: Use gcc -m options when building vdso Willy Tarreau
2011-02-06 23:23   ` [PATCH 20/23] tracing: Fix panic when lseek() called on "trace" opened for writing Willy Tarreau
2011-02-14 23:14     ` [Stable-review] " Ben Hutchings
2011-02-15  1:33       ` Steven Rostedt
2011-02-15  1:38         ` Ben Hutchings
2011-02-15  2:01           ` Steven Rostedt
2011-02-15  5:39       ` Willy Tarreau
2011-02-06 23:23   ` Willy Tarreau [this message]
2011-02-07 21:16     ` [PATCH 21/23] hvc_console: Fix race between hvc_close and hvc_remove Anton Blanchard
2011-02-07 22:11       ` Willy Tarreau
2011-02-06 23:23   ` [PATCH 22/23] hvc_console: Fix race between hvc_close and hvc_remove, again Willy Tarreau
2011-02-06 23:23   ` [PATCH 23/23] install_special_mapping skips security_file_mmap check Willy Tarreau

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