Re: [Qemu-devel] [RFC PATCH v4 14/15] slirp: handle race condition

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2013-04-17 10:39, Liu Ping Fan wrote:
> From: Liu Ping Fan <pingfank@linux.vnet.ibm.com>
> 
> Slirp and its peer can run on different context at the same time.
> Using lock to protect

What are the usage rules for this lock, what precisely is it protecting?
Is it ensured that we do not take the BQL while holding this one?

Jan

> 
> Signed-off-by: Liu Ping Fan <pingfank@linux.vnet.ibm.com>
> ---
>  slirp/slirp.c |   16 ++++++++++++++--
>  slirp/slirp.h |    3 +++
>  2 files changed, 17 insertions(+), 2 deletions(-)
> 
> diff --git a/slirp/slirp.c b/slirp/slirp.c
> index 883b7bd..6bfcc67 100644
> --- a/slirp/slirp.c
> +++ b/slirp/slirp.c
> @@ -206,6 +206,7 @@ Slirp *slirp_init(int restricted, struct in_addr vnetwork,
>  
>      slirp_init_once();
>  
> +    qemu_mutex_init(&slirp->lock);
>      slirp->restricted = restricted;
>  
>      if_init(slirp);
> @@ -248,6 +249,7 @@ void slirp_cleanup(Slirp *slirp)
>  
>      ip_cleanup(slirp);
>      m_cleanup(slirp);
> +    qemu_mutex_destroy(&slirp->lock);
>  
>      g_free(slirp->vdnssearch);
>      g_free(slirp->tftp_prefix);
> @@ -411,6 +413,7 @@ gboolean slirp_handler(gpointer data)
>      struct socket *so, *so_next;
>      int ret;
>  
> +    qemu_mutex_lock(&slirp->lock);
>      /*
>       * See if anything has timed out
>       */
> @@ -594,6 +597,7 @@ gboolean slirp_handler(gpointer data)
>      }
>  
>      if_start(slirp);
> +    qemu_mutex_unlock(&slirp->lock);
>      return true;
>  }
>  
> @@ -665,6 +669,7 @@ void slirp_input(Slirp *slirp, const uint8_t *pkt, int pkt_len)
>          return;
>  
>      proto = ntohs(*(uint16_t *)(pkt + 12));
> +    qemu_mutex_lock(&slirp->lock);
>      switch(proto) {
>      case ETH_P_ARP:
>          arp_input(slirp, pkt, pkt_len);
> @@ -688,6 +693,7 @@ void slirp_input(Slirp *slirp, const uint8_t *pkt, int pkt_len)
>      default:
>          break;
>      }
> +    qemu_mutex_unlock(&slirp->lock);
>  }
>  
>  /* Output the IP packet to the ethernet device. Returns 0 if the packet must be
> @@ -860,15 +866,21 @@ void slirp_socket_recv(Slirp *slirp, struct in_addr guest_addr, int guest_port,
>                         const uint8_t *buf, int size)
>  {
>      int ret;
> -    struct socket *so = slirp_find_ctl_socket(slirp, guest_addr, guest_port);
> +    struct socket *so;
> +
> +    qemu_mutex_lock(&slirp->lock);
> +    so = slirp_find_ctl_socket(slirp, guest_addr, guest_port);
>  
> -    if (!so)
> +    if (!so) {
> +        qemu_mutex_unlock(&slirp->lock);
>          return;
> +    }
>  
>      ret = soreadbuf(so, (const char *)buf, size);
>  
>      if (ret > 0)
>          tcp_output(sototcpcb(so));
> +    qemu_mutex_unlock(&slirp->lock);
>  }
>  
>  static void slirp_tcp_save(QEMUFile *f, struct tcpcb *tp)
> diff --git a/slirp/slirp.h b/slirp/slirp.h
> index 008360e..7ab0c70 100644
> --- a/slirp/slirp.h
> +++ b/slirp/slirp.h
> @@ -135,6 +135,7 @@ void free(void *ptr);
>  
>  #include "qemu/queue.h"
>  #include "qemu/sockets.h"
> +#include "qemu/thread.h"
>  
>  #include "libslirp.h"
>  #include "ip.h"
> @@ -207,6 +208,8 @@ struct Slirp {
>      u_int last_slowtimo;
>      int do_slowtimo;
>  
> +    /* lock to protect slirp running both on frontend or SlirpState context */
> +    QemuMutex lock;
>      /* virtual network configuration */
>      struct in_addr vnetwork_addr;
>      struct in_addr vnetwork_mask;
> 

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