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From: Anton Blanchard <anton@samba.org>
To: Willy Tarreau <w@1wt.eu>
Cc: linux-kernel@vger.kernel.org, stable@kernel.org,
	stable-review@kernel.org, Greg Kroah-Hartman <gregkh@suse.de>,
	Rusty Russell <rusty@rustcorp.com.au>,
	linuxppc-dev@ozlabs.org, Amit Shah <amit.shah@redhat.com>,
	Alan Cox <alan@lxorguk.ukuu.org.uk>
Subject: Re: [PATCH 21/23] hvc_console: Fix race between hvc_close and hvc_remove
Date: Tue, 8 Feb 2011 08:16:00 +1100	[thread overview]
Message-ID: <20110208081600.1a816af5@kryten> (raw)
In-Reply-To: <20110206232253.421321729@pcw.home.local>


Hi,

> 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().

I faintly remember this bug caused boot issues and the following patch
must be applied to fix it.

Anton
--

commit 320718ee074acce5ffced6506cb51af1388942aa
Author: Anton Blanchard <anton@samba.org>
Date:   Tue Apr 6 21:42:38 2010 +1000

    hvc_console: Fix race between hvc_close and hvc_remove
    
    I don't claim to understand the tty layer, but it seems like hvc_open and
    hvc_close should be balanced in their kref reference counting.
    
    Right now we get a kref every call to hvc_open:
    
            if (hp->count++ > 0) {
                    tty_kref_get(tty); <----- here
                    spin_unlock_irqrestore(&hp->lock, flags);
                    hvc_kick();
                    return 0;
            } /* else count == 0 */
    
            tty->driver_data = hp;
    
            hp->tty = tty_kref_get(tty); <------ or here if hp->count was 0
    
    But hvc_close has:
    
            tty_kref_get(tty);
    
            if (--hp->count == 0) {
    ...
                    /* Put the ref obtained in hvc_open() */
                    tty_kref_put(tty);
    ...
            }
    
            tty_kref_put(tty);
    
    Since the outside kref get/put balance we only do a single kref_put when
    count reaches 0.
    
    The patch below changes things to call tty_kref_put once for every
    hvc_close call, and with that my machine boots fine.
    
    Signed-off-by: Anton Blanchard <anton@samba.org>
    Acked-by: Amit Shah <amit.shah@redhat.com>
    Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/drivers/char/hvc_console.c b/drivers/char/hvc_console.c
index d3890e8..35cca4c 100644
--- a/drivers/char/hvc_console.c
+++ b/drivers/char/hvc_console.c
@@ -368,16 +368,12 @@ static void hvc_close(struct tty_struct *tty, struct file * filp)
 	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);
 

  reply	other threads:[~2011-02-07 21:16 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   ` [PATCH 21/23] hvc_console: Fix race between hvc_close and hvc_remove Willy Tarreau
2011-02-07 21:16     ` Anton Blanchard [this message]
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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