solos-pci: Fix race condition in tasklet RX handling

commit 1f6ea6e511e5ec730d8e88651da1b7b6e8fd1333 upstream.

We were seeing faults in the solos-pci receive tasklet when packets
arrived for a VCC which was currently being closed:

[18842.727906] EIP: [<e082f490>] br2684_push+0x19/0x234 [br2684] SS:ESP 0068:dfb89d14

[18845.090712] [<c13ecff3>] ? do_page_fault+0x0/0x2e1
[18845.120042] [<e082f490>] ? br2684_push+0x19/0x234 [br2684]
[18845.153530] [<e084fa13>] solos_bh+0x28b/0x7c8 [solos_pci]
[18845.186488] [<e084f711>] ? solos_irq+0x2d/0x51 [solos_pci]
[18845.219960] [<c100387b>] ? handle_irq+0x3b/0x48
[18845.247732] [<c10265cb>] ? irq_exit+0x34/0x57
[18845.274437] [<c1025720>] tasklet_action+0x42/0x69
[18845.303247] [<c102643f>] __do_softirq+0x8e/0x129
[18845.331540] [<c10264ff>] do_softirq+0x25/0x2a
[18845.358274] [<c102664c>] _local_bh_enable_ip+0x5e/0x6a
[18845.389677] [<c102666d>] local_bh_enable+0xb/0xe
[18845.417944] [<e08490a8>] ppp_unregister_channel+0x32/0xbb [ppp_generic]
[18845.458193] [<e08731ad>] pppox_unbind_sock+0x18/0x1f [pppox]

This patch uses an RCU-inspired approach to fix it. In the RX tasklet's
find_vcc() function we first refuse to use a VCC which already has the
ATM_VF_READY bit cleared. And in the VCC close function, we synchronise
with the tasklet to ensure that it can't still be using the VCC before
we continue and allow the VCC to be destroyed.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Tested-by: Nathan Williams <nathan@traverse.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/atm/solos-pci.c b/drivers/atm/solos-pci.c
index ded76c4c9f4f1599d6b8087eff93d9247e4f8526..36134221abd409d1dc1105b946ad59bd937654ce 100644 (file)
--- a/drivers/atm/solos-pci.c
+++ b/drivers/atm/solos-pci.c
@@ -781,7 +781,8 @@ static struct atm_vcc *find_vcc(struct atm_dev *dev, short vpi, int vci)
        sk_for_each(s, node, head) {
                vcc = atm_sk(s);
                if (vcc->dev == dev && vcc->vci == vci &&
-                   vcc->vpi == vpi && vcc->qos.rxtp.traffic_class != ATM_NONE)
+                   vcc->vpi == vpi && vcc->qos.rxtp.traffic_class != ATM_NONE &&
+                   test_bit(ATM_VF_READY, &vcc->flags))
                        goto out;
        }
        vcc = NULL;
@@ -907,6 +908,10 @@ static void pclose(struct atm_vcc *vcc)
        clear_bit(ATM_VF_ADDR, &vcc->flags);
        clear_bit(ATM_VF_READY, &vcc->flags);
 
+       /* Hold up vcc_destroy_socket() (our caller) until solos_bh() in the
+          tasklet has finished processing any incoming packets (and, more to
+          the point, using the vcc pointer). */
+       tasklet_unlock_wait(&card->tlet);
        return;
 }