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

[liu ping fan <qemulist@gmail.com>]

On Thu, Apr 18, 2013 at 3:13 PM, Jan Kiszka <jan.kiszka@siemens.com> wrote:
> 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?
>
It protect the slirp state, since slirp can be touched by slrip_input
called by frontend(ex, e1000), also it can be touched by its event
handler.  With this lock, we do not need BQL

Regards,
Pingfan


> 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;
>>
>
> --
> Siemens AG, Corporate Technology, CT RTC ITP SDP-DE
> Corporate Competence Center Embedded Linux