Re: [PATCH-rt 1/1] Fix spinlock issue in net/core/sock.c

[Jan Blunck <jblunck@gmail.com>]

On Thu, Jun 25, 2009 at 2:07 PM, Vivek Satpute<vivek@linsyssoft.com> wrote:
> Kernel panic's and reboot while doing network operations such ifconfig
> and ping on MIPS architecture after RT-patches applied.
>
> In case of CONFIG_PREEMPT_RT, after releasing the lock with
> "spin_unlock", context switch might occur before enabling the bottom
> half with local_bh_enable and this causes the kernel to panic.
> The issue is resolved by releasing the lock afer acquiring the mutex
> using spin_unlock_bh.
>
> Tested the fix on MIPS and X86 architecture.
>
> Signed-off-by: Vivek Satpute <vivek@linsyssoft.com>
> ---
> net/core/sock.c |    8 ++++++++
> 1 file changed, 8 insertions(+)
>
> Index: linux-2.6.28.4/net/core/sock.c
> ===================================================================
> --- linux-2.6.28.4.orig/net/core/sock.c
> +++ linux-2.6.28.4/net/core/sock.c
> @@ -1752,12 +1752,20 @@ void lock_sock_nested(struct sock *sk, i
>        if (sk->sk_lock.owned)
>                __lock_sock(sk);
>        sk->sk_lock.owned = 1;
> +
> +#ifndef CONFIG_PREEMPT_RT
>        spin_unlock(&sk->sk_lock.slock);
> +#endif
>        /*
>         * The sk_lock has mutex_lock() semantics here:
>         */
>        mutex_acquire(&sk->sk_lock.dep_map, subclass, 0, _RET_IP_);
> +
> +#ifdef CONFIG_PREEMPT_RT
> +       spin_unlock_bh(&sk->sk_lock.slock);
> +#else
>        local_bh_enable();
> +#endif
>  }
>

I don't think you should move the unlock after the mutex_acquire(). I
guess that this will lead to false positive lockdep warnings.

Anyway, I wonder why using spin_unlock_bh() is fixing the problem that
you are having. Do you have more context about the problem or maybe an
Oops or so?

Thanks,
Jan

>  EXPORT_SYMBOL(lock_sock_nested);
>
>
>
>
> Thanks and Regards,
> Vivek Satpute
> System Software Engineer
> LinSysSoft Technologies, Pune
>
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