Re: [PATCH] Bluetooth: fix crash by disabling tasklet in sock accept

["Gustavo F. Padovan" <padovan@profusion.mobi>]

Hi Andrei,

* Andrei Emeltchenko <andrei.emeltchenko.news@gmail.com> [2011-01-19 17:37:50 +0200]:

> Hi,
> 
> > From: Andrei Emeltchenko <andrei.emeltchenko@nokia.com>
> > 
> > Crash can happen when tasklet handling connect/disconnect requests
> > preempts socket accept. Can be reproduced with "l2test -r" on one
> > side and several "l2test -c -b 1000 -i hci0 -P 10 <bdaddr>" on the
> > other side.
> > 
> > ...
> > [ 3555.897247] Unable to handle kernel NULL pointer dereference at
> > virtual address 000000bc
> > [ 3555.915039] pgd = cab9c000
> > [ 3555.917785] [000000bc] *pgd=8bf3d031, *pte=00000000, *ppte=00000000
> > [ 3555.928314] Internal error: Oops: 17 [#1] PREEMPT
> > [ 3555.999786] CPU: 0       Not tainted   (2.6.32.21-13874-g67918ef #65)
> > ...
> > [ 3556.005981] PC is at bt_accept_unlink+0x20/0x58 [bluetooth]
> > [ 3556.011627] LR is at bt_accept_dequeue+0x3c/0xe8 [bluetooth]
> > ...
> > [ 3556.161285] [<bf0007fc>] (bt_accept_unlink+0x20/0x58 [bluetooth]) from
> > [<bf000870>] (bt_accept_dequeue+0x3c/0xe8 [bluetooth])
> > [ 3556.172729] [<bf000870>] (bt_accept_dequeue+0x3c/0xe8 [bluetooth])
> > from [<bf324df8>] (l2cap_sock_accept+0x100/0x15c [l2cap])
> > [ 3556.184082] [<bf324df8>] (l2cap_sock_accept+0x100/0x15c [l2cap]) from
> > [<c026a0a8>] (sys_accept4+0x120/0x1e0)
> > [ 3556.193969] [<c026a0a8>] (sys_accept4+0x120/0x1e0) from [<c002c9a0>]
> > (ret_fast_syscall+0x0/0x2c)
> > [ 3556.202819] Code: e5813000 e5901164 e580c160 e580c15c (e1d13bbc)
> > ...
> > 
> > Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@nokia.com>
> > ---
> >   net/bluetooth/af_bluetooth.c |       4 ++++
> >   1 files changed, 4 insertions(+), 0 deletions(-)
> > 
> > diff --git a/net/bluetooth/af_bluetooth.c b/net/bluetooth/af_bluetooth.c
> > index a6732b5..86386e9 100644
> > --- a/net/bluetooth/af_bluetooth.c
> > +++ b/net/bluetooth/af_bluetooth.c
> > @@ -199,6 +199,7 @@ struct sock *bt_accept_dequeue(struct sock *parent,
> > struct socket *newsock) 
> >       BT_DBG("parent %p", parent);
> >   
> > +    local_bh_disable();
> >       list_for_each_safe(p, n, &bt_sk(parent)->accept_q) {
> >           sk = (struct sock *) list_entry(p, struct bt_sock, accept_q);
> >   
> > @@ -217,11 +218,14 @@ struct sock *bt_accept_dequeue(struct sock
> > *parent, struct socket *newsock)             if (newsock)
> >                   sock_graft(sk, newsock);
> >               release_sock(sk);
> 
> I will change lock,release_sock to bh_lock,unlock_sock
> 
> when bh are disabled we do not need to mark
> socket as owned.

Looks a better idea.

-- 
Gustavo F. Padovan
http://profusion.mobi