Re: [patch 16/47] bluetooth: fix locking bug in the rfcomm socket cleanup handling

[Dave Young]

On Sat, Jun 14, 2008 at 8:10 AM, Greg KH <gregkh@xxxxxxx> wrote:
> -stable review patch.  If anyone has any objections, please let us know.
>
> ------------------
> From: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
>
> [ Upstream commit: 7dccf1f4e1696c79bff064c3770867cc53cbc71c ]

Hi greg
Please including following commit as well because it will cause another bug:
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=537d59af73d894750cff14f90fe2b6d77fbab15b

>
> in net/bluetooth/rfcomm/sock.c, rfcomm_sk_state_change() does the
> following operation:
>
>        if (parent && sock_flag(sk, SOCK_ZAPPED)) {
>                /* We have to drop DLC lock here, otherwise
>                 * rfcomm_sock_destruct() will dead lock. */
>                rfcomm_dlc_unlock(d);
>                rfcomm_sock_kill(sk);
>                rfcomm_dlc_lock(d);
>        }
> }
>
> which is fine, since rfcomm_sock_kill() will call sk_free() which will call
> rfcomm_sock_destruct() which takes the rfcomm_dlc_lock()... so far so good.
>
> HOWEVER, this assumes that the rfcomm_sk_state_change() function always gets
> called with the rfcomm_dlc_lock() taken. This is the case for all but one
> case, and in that case where we don't have the lock, we do a double unlock
> followed by an attempt to take the lock, which due to underflow isn't
> going anywhere fast.
>
> This patch fixes this by moving the stragling case inside the lock, like
> the other usages of the same call are doing in this code.
>
> This was found with the help of the www.kerneloops.org project, where this
> deadlock was observed 51 times at this point in time:
> http://www.kerneloops.org/search.php?search=rfcomm_sock_destruct
>
> Signed-off-by: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
> Acked-by: Marcel Holtmann <marcel@xxxxxxxxxxxx>
> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
> Signed-off-by: Chris Wright <chrisw@xxxxxxxxxxxx>
> ---
>  net/bluetooth/rfcomm/core.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> --- a/net/bluetooth/rfcomm/core.c
> +++ b/net/bluetooth/rfcomm/core.c
> @@ -423,8 +423,8 @@ static int __rfcomm_dlc_close(struct rfc
>
>                rfcomm_dlc_lock(d);
>                d->state = BT_CLOSED;
> -               rfcomm_dlc_unlock(d);
>                d->state_change(d, err);
> +               rfcomm_dlc_unlock(d);
>
>                skb_queue_purge(&d->tx_queue);
>                rfcomm_dlc_unlink(d);
>
> --
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-- 
Regards
dave
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