Re: [mm-patch] bluetooth: use GFP_ATOMIC in *_sock_create's sk_alloc

Masatake YAMATO
2006-07-28T13:13:16Z

Hi,

> On Fri, Jul 28, 2006 at 06:17:56PM +0900, Masatake YAMATO wrote:
> > > I think that the bluetooth-guard-bt_proto-with-rwlock.patch introduced the following
> > > BUG:
> > > [ 43.232000] BUG: sleeping function called from invalid context at mm/slab.c:2903
> > > [ 43.232000] in_atomic():1, irqs_disabled():0
> > > [ 43.232000] [<c0104114>] show_trace_log_lvl+0x197/0x1ba
> > > [ 43.232000] [<c010415e>] show_trace+0x27/0x29
> > > [ 43.232000] [<c010426e>] dump_stack+0x26/0x28
> > > [ 43.232000] [<c011ad1c>] __might_sleep+0xa2/0xaa
> > > [ 43.232000] [<c0173085>] __kmalloc+0x9c/0xb3
> > > [ 43.232000] [<c02f9295>] sk_alloc+0x1bc/0x1de
> > > [ 43.232000] [<c036d689>] hci_sock_create+0x42/0x8a
> > > [ 43.236000] [<c0366f40>] bt_sock_create+0xb5/0x154
> > > [ 43.236000] [<c02f69dc>] __sock_create+0x131/0x356
> > > [ 43.236000] [<c02f6c2f>] sock_create+0x2e/0x30
> > > [ 43.236000] [<c02f6c88>] sys_socket+0x27/0x53
> > > [ 43.240000] [<c02f7db5>] sys_socketcall+0xa9/0x277
> > > [ 43.240000] [<c0103131>] sysenter_past_esp+0x56/0x8d
> > > [ 43.240000] [<b7f38410>] 0xb7f38410
> > >
> > >
> > > This patch makes sk_alloc GFP_ATOMIC, because we are holding the bt_proto_rwlock, for
> > > the following functions:
> > > - bnep_sock_create
> > > - cmtp_sock_create
> > > - hci_sock_create
> > > - hidp_sock_create
> > > - l2cap_sock_create
> > > - rfcomm_sock_create
> > > - sco_sock_create
> >
> > There is very similar code in i net/socket.c(I guess some part of
> > bluetooth/af_bluetooth.c is derived from net/socket.c):
> >
> [... skip net/socket.c code ...]
> >
> > So there are two ways to avoid the bug:
> > 1. As proposed by Frederik, use sk_alloc with GFP_ATOMIC or
> > 2. use net_family_{read|writ}_{lock|unlock} in af_bluetooth.c.
> >
> I'd say that using a net_family_* like function set is much better,
> if only in terms of preemptibility.
>
> I'll write an implementation that allows to use the same code
> in socket.c and in af_bluetooth.c
>
> Regards,
> Frederik

I found one more similar code set at net/dccp/ccid.c for the same purpose:

/*
* The strategy is: modifications ccids vector are short, do not sleep and
* veeery rare, but read access should be free of any exclusive locks.
*/
static void ccids_write_lock(void)
{
spin_lock(&ccids_lock);
while (atomic_read(&ccids_lockct) != 0) {
spin_unlock(&ccids_lock);
yield();
spin_lock(&ccids_lock);
}
}

static inline void ccids_write_unlock(void)
{
spin_unlock(&ccids_lock);
}

static inline void ccids_read_lock(void)
{
atomic_inc(&ccids_lockct);
spin_unlock_wait(&ccids_lock);
}

static inline void ccids_read_unlock(void)
{
atomic_dec(&ccids_lockct);
}

I'm new to the kernel, however, I think it is better to unify
them into one and to give a good name.

Masatake YAMATO