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    SubjectRe: [mm-patch] bluetooth: use GFP_ATOMIC in *_sock_create's sk_alloc
    From
    > 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):

    static int __sock_create(int family, int type, int protocol, struct socket **res, int kern)
    {
    ...
    net_family_read_lock();
    ...
    if ((err = net_families[family]->create(sock, protocol)) < 0) {
    sock->ops = NULL;
    goto out_module_put;
    }
    ...
    net_family_read_unlock();
    return err;
    }

    I can find GFP_KERNEL is used to allocate object in
    net_families[family]->create(sock, protocol). e.g.:

    net/ipv4/af_inet.c:
    static int inet_create(struct socket *sock, int protocol)
    {
    ...
    sk = sk_alloc(PF_INET, GFP_KERNEL, answer_prot, 1);
    ...
    }

    Tricks are in net_family_read_lock and net_family_read_unlock:

    net/socket.c:
    static __inline__ void net_family_read_lock(void)
    {
    atomic_inc(&net_family_lockct);
    spin_unlock_wait(&net_family_lock);
    }

    static __inline__ void net_family_read_unlock(void)
    {
    atomic_dec(&net_family_lockct);
    }

    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 wonder which is better.

    Masatake YAMATO
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