On 12/03/2013 09:48 PM, Ding Tianhong wrote: > I have met the oops in Suse11 SP2, the kernel is 2.6.32.59-0.7-default: > > [64306.089036] BUG: unable to handle kernel NULL pointer dereference at 0000000000000008 > [64306.089343] IP: [<ffffffff812f8e36>] neigh_timer_handler+0x116/0x3b0 > [64306.089535] PGD 0 > [64306.089706] Oops: 0000 [#1] SMP > [64306.089935] last sysfs file: /sys/devices/pci0000:00/0000:00:03.0/0000:02:00.0/host0/target0:1:0/0:1:0:0/scsi_generic/sg0/dev > [64306.090142] Die func triggered, code:1 > [64306.090147] CPU 1 > [64306.090258] Supported: Yes, External > [64306.090262] Pid: 58359, comm: socknal_cd04 Tainted: P N 2.6.32.59-0.7-default #1 T3500 G3 > [64306.090266] RIP: 0010:[<ffffffff812f8e36>] [<ffffffff812f8e36>] neigh_timer_handler+0x116/0x3b0 > [64306.090272] RSP: 0018:ffff880c273499d8 EFLAGS: 00010206 > [64306.090275] RAX: 0000000000000000 RBX: ffff8801cddf1500 RCX: ffff8801cddf14f2 > [64306.090278] RDX: 0000000000000000 RSI: ffff8805e40d3a28 RDI: ffff8801cddf1500 > [64306.090281] RBP: ffff8805e40d3a28 R08: ffff8801cddf1530 R09: ffff880c27349b17 > [64306.090284] R10: 000000000000000e R11: ffffffff812f8e22 R12: ffff880185c0e840 > [64306.090287] R13: 0000000000000000 R14: ffff8805e40d3a60 R15: 0000000003484560 > [64306.090291] FS: 00007f081210e700(0000) GS:ffff880036420000(0000) knlGS:0000000000000000 > [64306.090295] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b > [64306.090297] CR2: 0000000000000008 CR3: 0000000001804000 CR4: 00000000000406e0 > [64306.090301] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > [64306.090304] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 > [64306.090308] Process socknal_cd04 (pid: 58359, threadinfo ffff880c27348000, task ffff880c25d02300) > [64306.090310] Stack: > [64306.090426] ffffffff8131f8e0 0000000000000003 ffff8801c189eb40 000000000000000a > [64306.090437] <0> ffffffff00000000 0000000000000002 ffff880c27349a30 ffffffffa304790c > [64306.090444] <0> 0000000000000246 000051010a010000 ffffffff81318357 31312d3300007fff > [64306.090450] <0> ffff880c27349bb8 0248456003484560 ffff8801c189eb40 ffffffff81869300 > [64306.090456] <0> ffff880185c0e840 ffff8801cddf1514 ffff8805e40d3a28 00000000000000d0 > [64306.090464] Call Trace: > > --------------------------- cut here ------------------------------------- > > I found the NULL place int the neigh_timer_handler, the neigh->ops is NULL, > so the calling of neigh->ops->solicit(neigh, skb) will panic, I found the > neigh has been freed via the kdump, the so I think the neigh was kfreed while > the neigh timer handler is running. > > The situation is that there are several server in the local lan: > A: 128.5.10.83 > B: 128.5.10.85 > C: 128.5.10.xx > > I panic the A by manual, and set B's IP to 128.5.10.83, so send broadcast to tell > the lan that B is 128.5.10.83, then the B panic, it is hard to appeared again, so > I only met once. > > I think the reason is that: > > CPU0 CPU1 > ----- ----- > <SOFTIRQ> > call_timer_fn(); > base->running_timer = neigh->timer; > neigh_timer_handler(); > neigh_release(); > write_lock(&neigh->lock); > del_timer(neigh->timer); > write_unlock(&neigh->lock); > write_lock(&neigh->lock); > kfree(neigh); > neigh->ops->solicit(); > > -------------------------------------------------------------------------- > > The reason is : besides deactivating the timer it also makes sure the handler > has finished executing on other CPUs, But the del_timer() just only detach the > timer and not wait for the timer finish executing on other CPUs. > the neigh->timer has the reference to the neigh, and this reference is released at the end of neigh_timer_handler. so the neigh should not be freed before the timer handler finished. As your description, some logic ignores the reference of neigh and calls neigh_destroy directly. You should find out the incorrect destroying of the neigh. > According to the David's opinion, the del_timer_sync() should belongs in > neigh_del_timer(), but the neigh_del_timer() will be called in > write_lock(&neigh->lock), it will occur deadlock if the timer is calling the same > lock, so del_timer_sync() should not be used in neigh_del_timer(). > > I fix the problem by add neigh->dead check in neigh_timer_handler(), because > if the neigh is in release path, the neigh is already in dead state, if the > timer is running on other CPUs, the timer will be finished and no problems > will occur when kfree the neighbour. > > I think the latest kernel still has the problem and make the patch for it. > > Suggested-by: David S. Miller <davem@xxxxxxxxxxxxx> > Signed-off-by: Ding Tianhong <dingtianhong@xxxxxxxxxx> > --- > net/core/neighbour.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/net/core/neighbour.c b/net/core/neighbour.c > index ca15f32..38f3d23 100644 > --- a/net/core/neighbour.c > +++ b/net/core/neighbour.c > @@ -888,6 +888,11 @@ static void neigh_timer_handler(unsigned long arg) > > write_lock(&neigh->lock); > > + if (neigh->dead) { > + pr_warn("neighbour is dead and should be destroyed\n"); > + goto out; > + } > + > state = neigh->nud_state; > now = jiffies; > next = now + HZ; > -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html