* [PATCH 21/23] hvc_console: Fix race between hvc_close and hvc_remove
[not found] <4beed4da27f06efb2c13d6ed48850634@local>
@ 2011-02-06 23:23 ` Willy Tarreau
2011-02-07 21:16 ` Anton Blanchard
0 siblings, 1 reply; 3+ messages in thread
From: Willy Tarreau @ 2011-02-06 23:23 UTC (permalink / raw)
To: linux-kernel, stable, stable-review
Cc: Greg Kroah-Hartman, Rusty Russell, linuxppc-dev, Amit Shah,
Willy Tarreau, Alan Cox
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;
}
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