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    SubjectRe: [patch] xenfb: fix xenfb suspend/resume race
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    On Thu, 2010-12-30 at 16:40 +0000, Konrad Rzeszutek Wilk wrote:
    > On Thu, Dec 30, 2010 at 08:56:16PM +0800, Joe Jin wrote:
    > > Hi,
    >
    > Joe,
    >
    > Patch looks good, however..
    >
    > I am unclear from your description whether the patch fixes
    > the problem (I would presume so). Or does it take a long time
    > to hit this race?

    I also don't see how the patch relates to the stack trace.

    Is the issue is that xenfb_send_event is called between xenfb_resume
    (which tears down the state, including evtchn->irq binding) and the
    probe/connect of the new fb?

    I suspect xenfb_resume should set info->update_wanted to 0. This will
    defer updates until we have successfully reconnected.

    Otherwise, since xenfb_resume also calls xenfb_connect I presume the
    call of xenfb_send_event is asynchronous. Which would suggest that some
    other locking is missing.

    Ian.


    >
    > >
    > > when do migration test, we hit the panic as below:
    > > <1>BUG: unable to handle kernel paging request at 0000000b819fdb98
    > > <1>IP: [<ffffffff812a588f>] notify_remote_via_irq+0x13/0x34
    > > <4>PGD 94b10067 PUD 0
    > > <0>Oops: 0000 [#1] SMP
    > > <0>last sysfs file: /sys/class/misc/autofs/dev
    > > <4>CPU 3
    > > <4>Modules linked in: autofs4(U) hidp(U) nfs(U) fscache(U) nfs_acl(U)
    > > auth_rpcgss(U) rfcomm(U) l2cap(U) bluetooth(U) rfkill(U) lockd(U) sunrpc(U)
    > > nf_conntrack_netbios_ns(U) ipt_REJECT(U) nf_conntrack_ipv4(U)
    > > nf_defrag_ipv4(U) xt_state(U) nf_conntrack(U) iptable_filter(U) ip_tables(U)
    > > ip6t_REJECT(U) xt_tcpudp(U) ip6table_filter(U) ip6_tables(U) x_tables(U)
    > > ipv6(U) parport_pc(U) lp(U) parport(U) snd_seq_dummy(U) snd_seq_oss(U)
    > > snd_seq_midi_event(U) snd_seq(U) snd_seq_device(U) snd_pcm_oss(U)
    > > snd_mixer_oss(U) snd_pcm(U) snd_timer(U) snd(U) soundcore(U)
    > > snd_page_alloc(U) joydev(U) xen_netfront(U) pcspkr(U) xen_blkfront(U)
    > > uhci_hcd(U) ohci_hcd(U) ehci_hcd(U)
    > > Pid: 18, comm: events/3 Not tainted 2.6.32
    > > RIP: e030:[<ffffffff812a588f>] [<ffffffff812a588f>]
    > > ify_remote_via_irq+0x13/0x34
    > > RSP: e02b:ffff8800e7bf7bd0 EFLAGS: 00010202
    > > RAX: ffff8800e61c8000 RBX: ffff8800e62f82c0 RCX: 0000000000000000
    > > RDX: 00000000000001e3 RSI: ffff8800e7bf7c68 RDI: 0000000bfffffff4
    > > RBP: ffff8800e7bf7be0 R08: 00000000000001e2 R09: ffff8800e62f82c0
    > > R10: 0000000000000001 R11: ffff8800e6386110 R12: 0000000000000000
    > > R13: 0000000000000007 R14: ffff8800e62f82e0 R15: 0000000000000240
    > > FS: 00007f409d3906e0(0000) GS:ffff8800028b8000(0000)
    > > GS:0000000000000000
    > > CS: e033 DS: 0000 ES: 0000 CR0: 000000008005003b
    > > CR2: 0000000b819fdb98 CR3: 000000003ee3b000 CR4: 0000000000002660
    > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    > > DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
    > > Process events/3 (pid: 18, threadinfo ffff8800e7bf6000, task
    > > f8800e7bf4540)
    > > Stack:
    > > 0000000000000200 ffff8800e61c8000 ffff8800e7bf7c00 ffffffff812712c9
    > > <0> ffffffff8100ea5f ffffffff81438d80 ffff8800e7bf7cd0 ffffffff812714ee
    > > <0> 0000000000000000 ffffffff81270568 000000000000e030 0000000000010202
    > > Call Trace:
    > > [<ffffffff812712c9>] xenfb_send_event+0x5c/0x5e
    > > [<ffffffff8100ea5f>] ? xen_restore_fl_direct_end+0x0/0x1
    > > [<ffffffff81438d80>] ? _spin_unlock_irqrestore+0x16/0x18
    > > [<ffffffff812714ee>] xenfb_refresh+0x1b1/0x1d7
    > > [<ffffffff81270568>] ? sys_imageblit+0x1ac/0x458
    > > [<ffffffff81271786>] xenfb_imageblit+0x2f/0x34
    > > [<ffffffff8126a3e5>] soft_cursor+0x1b5/0x1c8
    > > [<ffffffff8126a137>] bit_cursor+0x4b6/0x4d7
    > > [<ffffffff8100ea5f>] ? xen_restore_fl_direct_end+0x0/0x1
    > > [<ffffffff81438d80>] ? _spin_unlock_irqrestore+0x16/0x18
    > > [<ffffffff81269c81>] ? bit_cursor+0x0/0x4d7
    > > [<ffffffff812656b7>] fb_flashcursor+0xff/0x111
    > > [<ffffffff812655b8>] ? fb_flashcursor+0x0/0x111
    > > [<ffffffff81071812>] worker_thread+0x14d/0x1ed
    > > [<ffffffff81075a8c>] ? autoremove_wake_function+0x0/0x3d
    > > [<ffffffff81438d80>] ? _spin_unlock_irqrestore+0x16/0x18
    > > [<ffffffff810716c5>] ? worker_thread+0x0/0x1ed
    > > [<ffffffff810756e3>] kthread+0x6e/0x76
    > > [<ffffffff81012dea>] child_rip+0xa/0x20
    > > [<ffffffff81011fd1>] ? int_ret_from_sys_call+0x7/0x1b
    > > [<ffffffff8101275d>] ? retint_restore_args+0x5/0x6
    > > [<ffffffff81012de0>] ? child_rip+0x0/0x20
    > > Code: 6b ff 0c 8b 87 a4 db 9f 81 66 85 c0 74 08 0f b7 f8 e8 3b ff ff ff c9
    > > c3 55 48 89 e5 48 83 ec 10 0f 1f 44 00 00 89 ff 48 6b ff 0c <8b> 87 a4 db 9f
    > > 81 66 85 c0 74 14 48 8d 75 f0 0f b7 c0 bf 04 00
    > > RIP [<ffffffff812a588f>] notify_remote_via_irq+0x13/0x34
    > > RSP <ffff8800e7bf7bd0>
    > > CR2: 0000000b819fdb98
    > > ---[ end trace 098b4b74827595d0 ]---
    > > Kernel panic - not syncing: Fatal exception
    > > Pid: 18, comm: events/3 Tainted: G D 2.6.32
    > > Call Trace:
    > > [<ffffffff812a029e>] ? card_probe+0x99/0x123
    > > [<ffffffff81056a96>] panic+0xa5/0x162
    > > [<ffffffff8100ea5f>] ? xen_restore_fl_direct_end+0x0/0x1
    > > [<ffffffff81438d80>] ? _spin_unlock_irqrestore+0x16/0x18
    > > [<ffffffff81079824>] ? down_trylock+0x30/0x38
    > > [<ffffffff812a029e>] ? card_probe+0x99/0x123
    > > [<ffffffff8105744c>] ? console_unblank+0x23/0x6f
    > > [<ffffffff81056763>] ? print_oops_end_marker+0x23/0x25
    > > [<ffffffff812a029e>] ? card_probe+0x99/0x123
    > > [<ffffffff81439c76>] oops_end+0xb7/0xc7
    > > [<ffffffff810366de>] no_context+0x1f1/0x200
    > > [<ffffffff812a029e>] ? card_probe+0x99/0x123
    > > [<ffffffff81036931>] __bad_area_nosemaphore+0x183/0x1a6
    > > [<ffffffff812af119>] ? extract_buf+0xbd/0x134
    > > [<ffffffff81030c7b>] ? pvclock_clocksource_read+0x47/0x9e
    > > [<ffffffff810369de>] bad_area_nosemaphore+0x13/0x15
    > > [<ffffffff8143b0ed>] do_page_fault+0x147/0x26c
    > > [<ffffffff81439185>] page_fault+0x25/0x30
    > > [<ffffffff812a588f>] ? notify_remote_via_irq+0x13/0x34
    > > [<ffffffff812712c9>] xenfb_send_event+0x5c/0x5e
    > > [<ffffffff8100ea5f>] ? xen_restore_fl_direct_end+0x0/0x1
    > > [<ffffffff81438d80>] ? _spin_unlock_irqrestore+0x16/0x18
    > > [<ffffffff812714ee>] xenfb_refresh+0x1b1/0x1d7
    > > [<ffffffff81270568>] ? sys_imageblit+0x1ac/0x458
    > > [<ffffffff81271786>] xenfb_imageblit+0x2f/0x34
    > > [<ffffffff8126a3e5>] soft_cursor+0x1b5/0x1c8
    > > [<ffffffff8126a137>] bit_cursor+0x4b6/0x4d7
    > > [<ffffffff8100ea5f>] ? xen_restore_fl_direct_end+0x0/0x1
    > > [<ffffffff81438d80>] ? _spin_unlock_irqrestore+0x16/0x18
    > > [<ffffffff81269c81>] ? bit_cursor+0x0/0x4d7
    > > [<ffffffff812656b7>] fb_flashcursor+0xff/0x111
    > > [<ffffffff812655b8>] ? fb_flashcursor+0x0/0x111
    > > [<ffffffff81071812>] worker_thread+0x14d/0x1ed
    > > [<ffffffff81075a8c>] ? autoremove_wake_function+0x0/0x3d
    > > [<ffffffff81438d80>] ? _spin_unlock_irqrestore+0x16/0x18
    > > [<ffffffff810716c5>] ? worker_thread+0x0/0x1ed
    > > [<ffffffff810756e3>] kthread+0x6e/0x76
    > > [<ffffffff81012dea>] child_rip+0xa/0x20
    > > [<ffffffff81011fd1>] ? int_ret_from_sys_call+0x7/0x1b
    > > [<ffffffff8101275d>] ? retint_restore_args+0x5/0x6
    > > [<ffffffff81012de0>] ? child_rip+0x0/0x20
    > > [<ffffffff81012de0>] ? child_rip+0x0/0x20
    > >
    > > Check the source found this maybe caused by kernel tried to used not ready
    > > xenfb when resume.
    > >
    > > Below is the potential fix, please reivew it
    > >
    > > Signed-off-by: Joe Jin <joe.jin@oracle.com>
    > > Cc: Ian Campbell <ian.campbell@citrix.com>
    > > Cc: Jeremy Fitzhardinge <jeremy@goop.org>
    > > Cc: Andrew Morton <akpm@linux-foundation.org>
    > >
    > > ---
    > > xen-fbfront.c | 19 +++++++++++--------
    > > 1 file changed, 11 insertions(+), 8 deletions(-)
    > >
    > > diff --git a/drivers/video/xen-fbfront.c b/drivers/video/xen-fbfront.c
    > > index dc72563..367fb1c 100644
    > > --- a/drivers/video/xen-fbfront.c
    > > +++ b/drivers/video/xen-fbfront.c
    > > @@ -561,26 +561,24 @@ static void xenfb_init_shared_page(struct xenfb_info *info,
    > > static int xenfb_connect_backend(struct xenbus_device *dev,
    > > struct xenfb_info *info)
    > > {
    > > - int ret, evtchn;
    > > + int ret, evtchn, irq;
    > > struct xenbus_transaction xbt;
    > >
    > > ret = xenbus_alloc_evtchn(dev, &evtchn);
    > > if (ret)
    > > return ret;
    > > - ret = bind_evtchn_to_irqhandler(evtchn, xenfb_event_handler,
    > > + irq = bind_evtchn_to_irqhandler(evtchn, xenfb_event_handler,
    > > 0, dev->devicetype, info);
    > > - if (ret < 0) {
    > > + if (irq < 0) {
    > > xenbus_free_evtchn(dev, evtchn);
    > > xenbus_dev_fatal(dev, ret, "bind_evtchn_to_irqhandler");
    > > - return ret;
    > > + return irq;
    > > }
    > > - info->irq = ret;
    > > -
    > > again:
    > > ret = xenbus_transaction_start(&xbt);
    > > if (ret) {
    > > xenbus_dev_fatal(dev, ret, "starting transaction");
    > > - return ret;
    > > + goto unbind_irq;
    > > }
    > > ret = xenbus_printf(xbt, dev->nodename, "page-ref", "%lu",
    > > virt_to_mfn(info->page));
    > > @@ -602,15 +600,20 @@ static int xenfb_connect_backend(struct xenbus_device *dev,
    > > if (ret == -EAGAIN)
    > > goto again;
    > > xenbus_dev_fatal(dev, ret, "completing transaction");
    > > - return ret;
    > > + goto unbind_irq;
    > > }
    > >
    > > xenbus_switch_state(dev, XenbusStateInitialised);
    > > + info->irq = irq;
    > > return 0;
    > >
    > > error_xenbus:
    > > xenbus_transaction_end(xbt, 1);
    > > xenbus_dev_fatal(dev, ret, "writing xenstore");
    > > + unbind_irq:
    > > + printk(KERN_ERR "xenfb_connect_backend failed!\n");
    > > + unbind_from_irqhandler(irq, info);
    > > + xenbus_free_evtchn(dev, evtchn);
    > > return ret;
    > > }
    > >
    > >
    > >
    > > --
    > > Oracle <http://www.oracle.com>
    > > Joe Jin | Team Leader, Software Development | +8610.8278.6295
    > > ORACLE | Linux and Virtualization
    > > Incubator Building 2-A ZPark | Beijing China, 100094
    > >
    > >
    > > --
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