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Date:   Thu, 2 Mar 2017 13:12:45 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Wei Liu <wei.liu2@...rix.com>
Cc:     igor.druzhinin@...rix.com,
        xen-devel <xen-devel@...ts.xenproject.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        David Miller <davem@...emloft.net>,
        Paul Durrant <paul.durrant@...rix.com>
Subject: Re: BUG due to "xen-netback: protect resource cleaning on XenBus
 disconnect"

On 02/03/17 13:06, Wei Liu wrote:
> On Thu, Mar 02, 2017 at 12:56:20PM +0100, Juergen Gross wrote:
>> With commits f16f1df65 and 9a6cdf52b we get in our Xen testing:
>>
>> [  174.512861] switch: port 2(vif3.0) entered disabled state
>> [  174.522735] BUG: sleeping function called from invalid context at
>> /home/build/linux-linus/mm/vmalloc.c:1441
>> [  174.523451] in_atomic(): 1, irqs_disabled(): 0, pid: 28, name: xenwatch
>> [  174.524131] CPU: 1 PID: 28 Comm: xenwatch Tainted: G        W
>> 4.10.0upstream-11073-g4977ab6-dirty #1
>> [  174.524819] Hardware name: MSI MS-7680/H61M-P23 (MS-7680), BIOS V17.0
>> 03/14/2011
>> [  174.525517] Call Trace:
>> [  174.526217]  show_stack+0x23/0x60
>> [  174.526899]  dump_stack+0x5b/0x88
>> [  174.527562]  ___might_sleep+0xde/0x130
>> [  174.528208]  __might_sleep+0x35/0xa0
>> [  174.528840]  ? _raw_spin_unlock_irqrestore+0x13/0x20
>> [  174.529463]  ? __wake_up+0x40/0x50
>> [  174.530089]  remove_vm_area+0x20/0x90
>> [  174.530724]  __vunmap+0x1d/0xc0
>> [  174.531346]  ? delete_object_full+0x13/0x20
>> [  174.531973]  vfree+0x40/0x80
>> [  174.532594]  set_backend_state+0x18a/0xa90
>> [  174.533221]  ? dwc_scan_descriptors+0x24d/0x430
>> [  174.533850]  ? kfree+0x5b/0xc0
>> [  174.534476]  ? xenbus_read+0x3d/0x50
>> [  174.535101]  ? xenbus_read+0x3d/0x50
>> [  174.535718]  ? xenbus_gather+0x31/0x90
>> [  174.536332]  ? ___might_sleep+0xf6/0x130
>> [  174.536945]  frontend_changed+0x6b/0xd0
>> [  174.537565]  xenbus_otherend_changed+0x7d/0x80
>> [  174.538185]  frontend_changed+0x12/0x20
>> [  174.538803]  xenwatch_thread+0x74/0x110
>> [  174.539417]  ? woken_wake_function+0x20/0x20
>> [  174.540049]  kthread+0xe5/0x120
>> [  174.540663]  ? xenbus_printf+0x50/0x50
>> [  174.541278]  ? __kthread_init_worker+0x40/0x40
>> [  174.541898]  ret_from_fork+0x21/0x2c
>> [  174.548635] switch: port 2(vif3.0) entered disabled state
>>
>> I believe calling vfree() when holding a spin_lock isn't a good idea.
>>
> 
> Use vfree_atomic instead?

Hmm, isn't this overkill here?

You can just set a local variable with the address and do vfree() after
releasing the lock.


Juergen

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