On Mon, Oct 26, 2009 at 12:11:51PM +1030, Rusty Russell wrote:
> On Mon, 26 Oct 2009 03:33:40 am Michael S. Tsirkin wrote:
> > virtio net used to unlink skbs from send queues on error,
> > but ever since 48925e372f04f5e35fec6269127c62b2c71ab794
> > we do not do this. This causes guest data corruption and crashes
> > with vhost since net core can requeue the skb or free it without
> > it being taken off the list.
> >
> > This patch fixes this by queueing the skb after successfull
> > transmit.
>
> I originally thought that this was racy: as soon as we do add_buf, we need to
> make sure we're ready for the callback (for virtio_pci, it's ->kick, but we
> shouldn't rely on that).
Modified the guest slightly, and I am getting crashes again.
I didn't have time to debug this, but based on previous experience,
I reverted 48925e372f04f5e35fec6269127c62b2c71ab794,
and the crash went away.
Rusty, what do you say we just revert 48925e372f04f5e35fec6269127c62b2c71ab794
for now?
How to reproduce: I used my vhost trees, and modified drivers/vhost/vhost.c :
- vhost_workqueue = create_workqueue("vhost");
+ vhost_workqueue = create_singlethread_workqueue("vhost");
My guess is this modifies timing and uncovers more races,
but of course there is a possibility that the bug is in vhost.
Still, the fact that 2.6.31 and 48925e372f04f5e35fec6269127c62b2c71ab794
as a guest are both fine, this is a strong hint that
48925e372f04f5e35fec6269127c62b2c71ab794 is to blame.
[ 24.555691] BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
[ 24.556658] IP: [<ffffffffa003f1b1>] free_old_xmit_skbs+0x66/0xcd [virtio_net]
[ 24.556658] PGD 3e9ee067 PUD 3f38d067 PMD 0
[ 24.556658] Thread overran stack, or stack corrupted
[ 24.556658] Oops: 0002 [#1] SMP
[ 24.556658] last sysfs file: /sys/devices/virtual/input/input1/capabilities/sw
[ 24.556658] CPU 0
[ 24.556658] Modules linked in: virtio_net virtio_blk virtio_pci virtio_ring virtio af_packet aacraid [last unloaded: scsi_wait_scan]
[ 24.556658] Pid: 0, comm: swapper Tainted: G W 2.6.32-rc4-net #6
[ 24.556658] RIP: 0010:[<ffffffffa003f1b1>] [<ffffffffa003f1b1>] free_old_xmit_skbs+0x66/0xcd [virtio_net]
[ 24.556658] RSP: 0018:ffff880001c03d70 EFLAGS: 00010202
[ 24.556658] RAX: ffff88003e951418 RBX: ffff88003e953398 RCX: 0000000000000000
[ 24.556658] RDX: 0000000000000000 RSI: ffff880001c03d84 RDI: ffff88003e953398
[ 24.556658] RBP: ffff880001c03db0 R08: ffff88003e2c949c R09: 00000000ffffffff
[ 24.556658] R10: ffff880001c03f78 R11: 00000000fffbcc57 R12: ffff88003e65cdc0
[ 24.556658] R13: 0000000000000000 R14: 2000000000000000 R15: ffff880001c03d84
[ 24.556658] FS: 0000000000000000(0000) GS:ffff880001c00000(0000) knlGS:0000000000000000
[ 24.556658] CS: 0010 DS: 0018 ES: 0018 CR0: 000000008005003b
[ 24.556658] CR2: 0000000000000008 CR3: 000000003eee4000 CR4: 00000000000006b0
[ 24.556658] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 24.556658] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[ 24.556658] Process swapper (pid: 0, threadinfo ffffffff8174e000, task ffffffff817c09f0)
[ 24.556658] Stack:
[ 24.556658] 0000000000000002 0000000000000000 0000000000000000 ffff88003e953398
[ 24.556658] <0> ffff88003e953398 ffff88003e65cdc0 ffff88003e65c800 ffff88003e65ce70
[ 24.556658] <0> ffff880001c03df0 ffffffffa003fb35 ffff88003e65cc28 ffff88003e953398
[ 24.556658] Call Trace:
[ 24.556658] <IRQ>
[ 24.556658] [<ffffffffa003fb35>] start_xmit+0x38/0x15f [virtio_net]
[ 24.556658] [<ffffffff813ff768>] dev_hard_start_xmit+0x26c/0x2d3
[ 24.556658] [<ffffffff81412016>] sch_direct_xmit+0x5a/0x157
[ 24.556658] [<ffffffff814121cf>] __qdisc_run+0xbc/0xdd
[ 24.556658] [<ffffffff813fce1c>] net_tx_action+0xc2/0x120
[ 24.556658] [<ffffffff81047efe>] __do_softirq+0xd8/0x192
[ 24.556658] [<ffffffff8100cb3c>] call_softirq+0x1c/0x28
[ 24.556658] [<ffffffff8100ddb7>] do_softirq+0x33/0x6b
[ 24.556658] [<ffffffff81047d5c>] irq_exit+0x36/0x75
[ 24.556658] [<ffffffff8100d692>] do_IRQ+0xa8/0xbf
[ 24.556658] [<ffffffff8100c3d3>] ret_from_intr+0x0/0xa
[ 24.556658] <EOI>
[ 24.556658] [<ffffffff81011de3>] ? default_idle+0x31/0x46
[ 24.556658] [<ffffffff81011dc5>] ? default_idle+0x13/0x46
[ 24.556658] [<ffffffff8100ae53>] ? cpu_idle+0x55/0x8d
[ 24.556658] [<ffffffff814d1982>] ? rest_init+0x66/0x68
[ 24.556658] [<ffffffff818adc5d>] ? start_kernel+0x360/0x36b
[ 24.556658] [<ffffffff818ad29a>] ? x86_64_start_reservations+0xaa/0xae
[ 24.556658] [<ffffffff818ad37f>] ? x86_64_start_kernel+0xe1/0xe8
[ 24.556658] Code: fc 26 00 00 00 75 75 41 ff 8c 24 c0 00 00 00 48 89 df 48 8b 13 48 8b 43 08 48 c7 03 00 00 00 00 48 c7 43 08 00 00 00 00 48 89 10 <48> 89 42 08 49 8b 54 24 20 8b 43 68 48 01 82 98 00 00 00 49 8b
[ 24.556658] RIP [<ffffffffa003f1b1>] free_old_xmit_skbs+0x66/0xcd [virtio_net]
[ 24.556658] RSP <ffff880001c03d70>
[ 24.556658] CR2: 0000000000000008
[ 24.722629] ---[ end trace 6ac04221a0ae018b ]---
[ 24.725010] Kernel panic - not syncing: Fatal exception in interrupt
[ 24.727696] Pid: 0, comm: swapper Tainted: G D W 2.6.32-rc4-net #6
[ 24.730447] Call Trace:
[ 24.732443] <IRQ> [<ffffffff814eb553>] panic+0x75/0x127
[ 24.735097] [<ffffffff814ee350>] oops_end+0xaa/0xba
[ 24.737520] [<ffffffff81029002>] no_context+0x1ea/0x1f9
[ 24.740024] [<ffffffff810291c4>] __bad_area_nosemaphore+0x1b3/0x1d9
[ 24.742779] [<ffffffff810291f8>] bad_area_nosemaphore+0xe/0x10
[ 24.745399] [<ffffffff814ef73c>] do_page_fault+0x186/0x2c3
[ 24.748009] [<ffffffff814ed8bf>] page_fault+0x1f/0x30
[ 24.750463] [<ffffffffa003f1b1>] ? free_old_xmit_skbs+0x66/0xcd [virtio_net]
[ 24.753299] [<ffffffffa003fb35>] start_xmit+0x38/0x15f [virtio_net]
[ 24.755990] [<ffffffff813ff768>] dev_hard_start_xmit+0x26c/0x2d3
[ 24.758635] [<ffffffff81412016>] sch_direct_xmit+0x5a/0x157
[ 24.761204] [<ffffffff814121cf>] __qdisc_run+0xbc/0xdd
[ 24.763693] [<ffffffff813fce1c>] net_tx_action+0xc2/0x120
[ 24.766236] [<ffffffff81047efe>] __do_softirq+0xd8/0x192
[ 24.768754] [<ffffffff8100cb3c>] call_softirq+0x1c/0x28
[ 24.771326] [<ffffffff8100ddb7>] do_softirq+0x33/0x6b
[ 24.773793] [<ffffffff81047d5c>] irq_exit+0x36/0x75
[ 24.776241] [<ffffffff8100d692>] do_IRQ+0xa8/0xbf
[ 24.778705] [<ffffffff8100c3d3>] ret_from_intr+0x0/0xa
[ 24.781191] <EOI> [<ffffffff81011de3>] ? default_idle+0x31/0x46
[ 24.783961] [<ffffffff81011dc5>] ? default_idle+0x13/0x46
[ 24.786487] [<ffffffff8100ae53>] ? cpu_idle+0x55/0x8d
[ 24.788967] [<ffffffff814d1982>] ? rest_init+0x66/0x68
[ 24.791448] [<ffffffff818adc5d>] ? start_kernel+0x360/0x36b
[ 24.794014] [<ffffffff818ad29a>] ? x86_64_start_reservations+0xaa/0xae
[ 24.796747] [<ffffffff818ad37f>] ? x86_64_start_kernel+0xe1/0xe8
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