Messages in this thread | | | Date | Thu, 4 Nov 2010 13:47:18 +0800 | From | Américo Wang <> | Subject | Re: [regression, 2.6.37-rc1] 'ip link tap0 up' stuck in do_exit() |
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On Thu, Nov 04, 2010 at 11:21:40AM +1100, Dave Chinner wrote: >On Wed, Nov 03, 2010 at 10:29:36PM +1100, Dave Chinner wrote: >> On Wed, Nov 03, 2010 at 09:34:48PM +1100, Dave Chinner wrote: >> > On Wed, Nov 03, 2010 at 08:13:22AM +0100, Eric Dumazet wrote: >> > > Le mercredi 03 novembre 2010 à 17:26 +1100, Dave Chinner a écrit : >> > > > Folks, >> > > > >> > > > Starting up KVM on a current mainline kernel using the tap >> > > > device for the networking is resulting in the ip process tryin gto >> > > > up the tap interface hanging. KVM is started with this networking >> > > > config: >> > > > >> > > > .... >> > > > -net nic,vlan=0,macaddr=00:e4:b6:63:63:6d,model=virtio \ >> > > > -net tap,vlan=0,script=/vm-images/qemu-ifup,downscript=no \ >> > > > .... >> > > > >> > > > And the script is effectively: >> > > > >> > > > switch=br0 >> > > > if [ -n "$1" ];then >> > > > /usr/bin/sudo /sbin/ip link set $1 up >> > > > sleep 0.5s >> > > > /usr/bin/sudo /usr/sbin/brctl addif $switch $1 >> > > > exit 0 >> > > > fi >> > > > exit 1 >> > > > >> > > > This is resulting in the command 'ip link set tap0 up' hanging as a zombie: >> > > > >> > > > root 3005 1 0 16:53 pts/3 00:00:00 /bin/sh /vm-images/qemu-ifup tap0 >> > > > root 3011 3005 0 16:53 pts/3 00:00:00 /usr/bin/sudo /sbin/ip link set tap0 up >> > > > root 3012 3011 0 16:53 pts/3 00:00:00 [ip] <defunct> >> > > > >> > > > In do_exit() with this trace: >> > > > >> > > > [ 1630.782255] ip x ffff88063fcb3600 0 3012 3011 0x00000000 >> > > > [ 1630.789121] ffff880631328000 0000000000000046 0000000000000000 ffff880633104380 >> > > > [ 1630.796524] 0000000000013600 ffff88062f031fd8 0000000000013600 0000000000013600 >> > > > [ 1630.803925] ffff8806313282d8 ffff8806313282e0 ffff880631328000 0000000000013600 >> > > > [ 1630.811324] Call Trace: >> > > > [ 1630.813760] [<ffffffff8104a90d>] ? do_exit+0x716/0x724 >> > > > [ 1630.818964] [<ffffffff8104a995>] ? do_group_exit+0x7a/0xa4 >> > > > [ 1630.824512] [<ffffffff8104a9d1>] ? sys_exit_group+0x12/0x16 >> > > > [ 1630.830149] [<ffffffff81009a82>] ? system_call_fastpath+0x16/0x1b >> > > > >> > > > The address comes down to the schedule() call: >> > > > >> > > > (gdb) l *(do_exit+0x716) >> > > > 0xffffffff8104a90d is in do_exit (kernel/exit.c:1034). >> > > > 1029 preempt_disable(); >> > > > 1030 exit_rcu(); >> > > > 1031 /* causes final put_task_struct in finish_task_switch(). */ >> > > > 1032 tsk->state = TASK_DEAD; >> > > > 1033 schedule(); >> > > > 1034 BUG(); >> > > > 1035 /* Avoid "noreturn function does return". */ >> > > > 1036 for (;;) >> > > > 1037 cpu_relax(); /* For when BUG is null */ >> > > > 1038 } >> > > > >> > > > Needless to say, KVM is not starting up. This works just fine on >> > > > 2.6.35.1 and so is a regression. I can't do a lot of testing on this as >> > > > the host is the machine that hosts all my build and test environments.... >> > > > >> > > > Cheers, >> > > > >> > > > Dave. >> > > >> > > Could it be the same problem than >> > > >> > > http://kerneltrap.com/mailarchive/linux-netdev/2010/10/23/6288128 >> > > >> > > Try to revert bee31369ce16fc3898ec9a54161248c9eddb06bc ? >> > >> > It's working fine on 2.6.36 right now, so it's something that came in >> > with the .37 merge cycle... >> >> Actually, the machine isn't running a 2.6.36 kernel (it had booted >> to the working .35 kernel and I didn't notice). So i've just tested >> a 2.6.36 kernel, and the problem _is present_ in 2.6.36. I've >> reverted the above commit but that does not fix the problem. > >Ok, so further investigation has shown I can reproduce this on >2.6.32 and 2.6.35. It's not a new bug, nor do I think that it is >a networking bug as it is not specific to the ip command. > >The trigger for the problem is actually an upgrade of the sudo >package in debian unstable which changed the behaviour of sudo (has >some per-login/pty restriction on it now). Basically, the startup >script I'm running does: > >sudo kvm ..... > >which then executes the qemu-ifup bash script which does: > > sudo ip .... > sudo brctl ... > >because at one point KVM did not create the tap device automatically >and so kvm could be run as a user with only the ifup script >requiring privileges to create the tap device and mark it up. When >KVM started creating the tap device, I added the sudo to the KVM >script, an everything worked again. > >Now if I take the 'sudo' out of the ifup script, the hang goes away. >I first removed it from the ip command, and then the brctl command >hung in the same way the ip command was hanging. Hence my thoughts >that it is not directly related to networking utilities. >Unfortunately, it is not trivial to reproduce as I could only >trigger it through this kvm method, not on the command line. e.g: > >$ sudo bash -c "sudo ip link set tap1 up" > >does not hang. > >This sudo package upgrade coincided with kernel upgrades, and so >that lead to my confusion about where it occurred and what triggered >it. Still, it appears to be a bug that has been around for some >time..... >
Interesting, the scheduler failed to put the dead task out of run queue, so to me this is likely to be a scheduler bug. I have no idea how sudo can change the behaviour here.
Another guess is we need a smp_wmb() before schedule() above.
We need to Cc Oleg and Ingo. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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