Re: port-xen/47057: Xen NetBSD DomU file system trash under Linux Dom0

[Roger Pau Monné <royger%NetBSD.org@localhost>]

The following reply was made to PR port-xen/47057; it has been noted by GNATS.

From: =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= <royger%NetBSD.org@localhost>
To: gnats-bugs%netbsd.org@localhost
Cc: port-xen-maintainer%netbsd.org@localhost, gnats-admin%netbsd.org@localhost, 
        netbsd-bugs%netbsd.org@localhost
Subject: Re: port-xen/47057: Xen NetBSD DomU file system trash under Linux Dom0
Date: Fri, 12 Oct 2012 17:52:22 +0200

 On Thu, Oct 11, 2012 at 7:30 PM, Manuel Bouyer 
<bouyer%antioche.eu.org@localhost> wrote:
 > The following reply was made to PR port-xen/47057; it has been noted by 
 > GNATS.
 >
 > From: Manuel Bouyer <bouyer%antioche.eu.org@localhost>
 > To: gnats-bugs%NetBSD.org@localhost
 > Cc: port-xen-maintainer%NetBSD.org@localhost, 
 > gnats-admin%NetBSD.org@localhost,
 >         netbsd-bugs%NetBSD.org@localhost
 > Subject: Re: port-xen/47057: Xen NetBSD DomU file system trash under Linux
 >  Dom0
 > Date: Thu, 11 Oct 2012 19:28:51 +0200
 >
 >  On Thu, Oct 11, 2012 at 05:20:00PM +0000, royger%NetBSD.org@localhost wrote:
 >  > >Fix:
 >  > I'm not sure about this, but I think we have a problem with reentrancy of 
 > the xen event channel callback (do_hypervisor_callback in 
 > hypervisor_machdep.c), but I haven't been able to find a fix for this.
 >
 >
 >  Can you expand on this ? AFAIK this code is safe.
 
 I'm not sure, but I think we might have a problem when we call
 intr_biglock_wrapper, this function takes the kernel_lock, but just
 before calling it we call sti(), which allows further hypervisor
 callbacks. Isn't it posible that another hypervisor callback
 interrupts the execution of the handler, leaving the kernel_lock held
 and thus locking the system when this new callback tries to execute a
 handler?