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From: Andreas Hartmann <andihartmann@freenet.de>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>,
	linux-pci <linux-pci@vger.kernel.org>
Subject: Re: Hard and silent lock up since linux 3.14 with PCIe pass through (vfio)
Date: Thu, 30 Oct 2014 17:35:52 +0100
Message-ID: <545268E8.3080107@maya.org> (raw)
In-Reply-To: <1414615824.27420.281.camel@ul30vt.home>

Alex Williamson wrote:
> On Wed, 2014-10-29 at 20:43 +0100, Andreas Hartmann wrote:
[...]
>> Therefore, I never should need pci_save_vc_state and
>> pci_restore_vc_state. Thus, it should be ok to add "return" at the
>> beginning of each of these function, true? Then it should work.
>>
>> I tested it. It worked.
>>
>> But if I'm removing only one of these returns either in
>> pci_save_vc_state or pci_restore_vc_state, the machine hangs again.
>>
>> Therefore, there must be something odd going on in the for loops. Isn't
>> it possible to add some useful debug code to these loops to see what's
>> really going on? But the output *must* go to the actual console,
>> otherwise I can't see it!
>>
>>
>> int pci_save_vc_state(struct pci_dev *dev)
>> {
>>         return 0; // must be set
>>         int i;
>>
>>         for (i = 0; i < ARRAY_SIZE(vc_caps); i++) {
		   // continue; -> works
>>                 int pos, ret;
>>                 struct pci_cap_saved_state *save_state;
		   // continue does not work!

--> Most probably the

            struct pci_cap_saved_state *save_state;

    makes the system hang!  ARRAY_SIZE(vc_caps) is 3 and the whole
    function is called 3 times when starting the vm.

>>
>>                 pos = pci_find_ext_capability(dev, vc_caps[i].id);
>>                 if (!pos || !pci_vc_needs_save(dev, vc_caps[i].id))
>>                         continue;
> 
> Take the next logical step, comment out the if here and we'll statically
> take the continue.  Does it still fail?  If so, move the continue above
> the call to pci_find_ext_capability(), if not...
> 
>>
>>                 save_state = pci_find_saved_ext_cap(dev, vc_caps[i].id);
> 
> If not, add a continue; here.  Unless my pci_vc_needs_save() function is
> broken, we shouldn't be getting here anyway.
> 
>>                 if (!save_state) {
>>                         dev_err(&dev->dev, "%s buffer not found in %s\n",
>>                                 vc_caps[i].name, __func__);
>>                         return -ENOMEM;
>>                 }
>>
>>                 printk("%s doing %s save on %s\n", __func__, vc_caps[i].name, pci_name(dev));
>>                 ret = pci_vc_do_save_buffer(dev, pos, save_state, true);
>>                 if (ret) {
>>                         dev_err(&dev->dev, "%s save unsuccessful %s\n",
>>                                 vc_caps[i].name, __func__);
>>                         return ret;
>>                 }
>>         }
>>
>>         return 0;
>> }
>>
>>
>> void pci_restore_vc_state(struct pci_dev *dev)
>> {
>>         return; // must be set
>>         int i;
>>
>>         for (i = 0; i < ARRAY_SIZE(vc_caps); i++) {
>>                 int pos;
>>                 struct pci_cap_saved_state *save_state;
>>
>>                 pos = pci_find_ext_capability(dev, vc_caps[i].id);
>>                 save_state = pci_find_saved_ext_cap(dev, vc_caps[i].id);
> 
> This should never find a save_state with the pci_vc_needs_save() patch,
> so we should always take the branch below.  Comment out the if (... and
> leave the continue, does the behavior change?  If so, add a continue;
> line above pci_find_saved_ext_cap(), does it work?  If not, add another
> continue above pci_find_ext_capability().
> 
>>                 if (!save_state || !pos)
>>                         continue;
>>
>>                 printk("%s doing %s restore on %s\n", __func__, vc_caps[i].name, pci_name(dev));
>>                 pci_vc_do_save_buffer(dev, pos, save_state, false);
>>         }
>> }
> 
> In the "working" case with Bjorn's patch, are you actually trying to use
> the device or just testing to see if the system survives reset?  You
> might at least want to run lspci -xxxx on it after reset to make sure
> it's really there.  Thanks,
> 
> Alex
> 


  parent reply index

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-09-23 19:03 Andreas Hartmann
2014-09-23 20:07 ` Alex Williamson
2014-09-24 14:54   ` Andreas Hartmann
2014-09-24 17:16     ` Andreas Hartmann
2014-10-10  9:39   ` Andreas Hartmann
2014-10-10 14:37     ` Bjorn Helgaas
2014-10-10 14:49       ` Andreas Hartmann
2014-10-10 15:55         ` Bjorn Helgaas
2014-10-10 16:09           ` Andreas Hartmann
2014-10-10 16:41             ` Bjorn Helgaas
2014-10-10 22:32               ` Andreas Hartmann
2014-10-10 22:54                 ` Bjorn Helgaas
2014-10-11  6:20                   ` Andreas Hartmann
2014-10-15  8:04                     ` Alex Williamson
2014-10-17  1:04                       ` Andreas Hartmann
2014-10-21 21:06                         ` Alex Williamson
2014-10-21 21:32                           ` Alex Williamson
2014-10-22 16:22                             ` Andreas Hartmann
2014-10-22 20:36                               ` Alex Williamson
2014-10-23 16:00                                 ` Andreas Hartmann
2014-10-23 16:33                                   ` Alex Williamson
2014-10-23 17:12                                     ` Andreas Hartmann
2014-10-23 17:33                                     ` Andreas Hartmann
2014-10-23 19:37                                       ` Alex Williamson
2014-10-24 14:21                                         ` Andreas Hartmann
2014-10-25  6:03                                         ` Andreas Hartmann
2014-10-28 21:51                                           ` Alex Williamson
2014-10-29 16:47                                             ` Andreas Hartmann
2014-10-29 17:44                                               ` Alex Williamson
2014-10-29 17:57                                                 ` Andreas Hartmann
2014-10-29 18:16                                                   ` Alex Williamson
2014-10-29 19:43                                                     ` Andreas Hartmann
2014-10-29 20:50                                                       ` Alex Williamson
2014-10-29 21:35                                                         ` Andreas Hartmann
2014-10-30 16:35                                                         ` Andreas Hartmann [this message]
2014-10-30 16:58                                                           ` Alex Williamson
2014-10-30 19:09                                                             ` Andreas Hartmann
2014-10-30 19:45                                                               ` Alex Williamson
2014-10-30 20:21                                                                 ` Andreas Hartmann
2014-10-22 15:34                           ` Andreas Hartmann
2014-10-22 16:02                             ` Alex Williamson
2014-10-22 16:20                               ` Andreas Hartmann

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