From mboxrd@z Thu Jan  1 00:00:00 1970
From: Keir Fraser <keir@xen.org>
Subject: Re: Xen randomly stuck in mdelay() during MP
 initialization
Date: Wed, 11 Jan 2012 15:27:10 +0000
Message-ID: <CB335ACE.371D2%keir@xen.org>
References: <CAKZ=5EVXak0SBJAY1gft4qxYFsBavrLYjxJV4tViUST_9uNUMw@mail.gmail.com>
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To: Julian Pidancet <julian.pidancet@gmail.com>
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On 11/01/2012 14:51, "Julian Pidancet" <julian.pidancet@gmail.com> wrote:

> On Wed, Jan 11, 2012 at 1:28 PM, Keir Fraser <keir.xen@gmail.com> wrote:
>> On 11/01/2012 13:06, "Julian Pidancet" <julian.pidancet@gmail.com> wrote:
>> =

>>> Hi,
>>> =

>>> When trying to boot xen 4.1 on new hardware, Xen become stuck in
>>> wakeup_secondary_cpu() in the mdelay function.
>>> =

>>> =A0 =A0 Dprintk("Waiting for send to finish...\n");
>>> =A0 =A0 timeout =3D 0;
>>> =A0 =A0 do {
>>> =A0 =A0 =A0 =A0 Dprintk("+");
>>> =A0 =A0 =A0 =A0 udelay(100);
>>> =A0 =A0 =A0 =A0 if ( !x2apic_enabled )
>>> =A0 =A0 =A0 =A0 =A0 =A0 send_status =3D apic_read(APIC_ICR) & APIC_ICR_=
BUSY;
>>> =A0 =A0 } while ( send_status && (timeout++ < 1000) );
>>> =

>>> =A0 =A0 printk("before mdelay\n");
>>> =A0 =A0 mdelay(10);
>>> =A0 =A0 printk("after mdelay\n");
>>> =

>>> =A0 =A0 Dprintk("Deasserting INIT.\n");
>>> =

>>> The hang can happen randomly with any of the CPUs to wake up and
>>> sometime doesn't happen at all.
>>> Replacing mdelay(10) with udelay(10) seems to fix the issue.
>> =

>> Do you see this in xen-unstable? Hopefully it is working there, and we c=
an
>> simply backport the fix.
>> =

> =

> I checked yesterday and the code of this function is the same in
> xen-unstable, but I don't encounter the problem with xen-unstable.

Well that would be because the code of this function is not the same in
xen-4.1 and xen-unstable.

> What concerns me is that this is the only place in the function where
> mdelay() is used, the rest of the function seems to be using udelay().
> What's the difference between the two ?
> Does mdelay() relies on some form of timer to execute ?

mdelay(ms) just calls udelay(1000) ms times.

 -- Keir