[PATCH 19/19] UML - Make mconsole version requests happen in a process

[PATCH 19/19] UML - Make mconsole version requests happen in a process

[Jeff Dike]

Handling a host mconsole version request must be done in a process context
rather than interrupt context now that utsname information can be 
process-specific rather than global.

Signed-off-by: Jeff Dike <jdike@addtoit.com>

Index: linux-2.6.16/arch/um/drivers/mconsole_user.c
===================================================================
--- linux-2.6.16.orig/arch/um/drivers/mconsole_user.c
+++ linux-2.6.16/arch/um/drivers/mconsole_user.c
@@ -18,7 +18,12 @@
 #include "umid.h"
 
 static struct mconsole_command commands[] = {
-	{ "version", mconsole_version, MCONSOLE_INTR },
+	/* With uts namespaces, uts information becomes process-specific, so
+	 * we need a process context.  If we try handling this in interrupt
+	 * context, we may hit an exiting process without a valid uts
+	 * namespace.
+	 */
+	{ "version", mconsole_version, MCONSOLE_PROC },
 	{ "halt", mconsole_halt, MCONSOLE_PROC },
 	{ "reboot", mconsole_reboot, MCONSOLE_PROC },
 	{ "config", mconsole_config, MCONSOLE_PROC },

RE: [uml-devel] [PATCH 19/19] UML - Make mconsole version requestshappen in a process

[Brock, Anthony - NET]

So what impact does this have on the following quote from
http://user-mode-linux.sourceforge.net/mconsole.html :


It's a simple no-op which can be used to check that a UML is running.
It's also a way of sending an interrupt to the UML. This is sometimes
useful on SMP hosts, where there's a bug which causes signals to UML to
be lost, often causing it to appear to hang. Sending such a UML the
mconsole version command is a good way to 'wake it up' before networking
has been enabled, as it does not do anything to the function of the UML.


I'm running UML on an SMP machine, but have never encountered the "hang"
issue. Is this text still accurate? Also, can this command still be used
to "wake up" a UML process? Is this still the recommended means for
verifying that a UML process if running?

Tony

> -----Original Message-----
> From: user-mode-linux-devel-bounces@lists.sourceforge.net 
> [mailto:user-mode-linux-devel-bounces@lists.sourceforge.net] 
> On Behalf Of Jeff Dike
> Sent: Thursday, July 06, 2006 5:34 PM
> To: akpm@osdl.org
> Cc: linux-kernel@vger.kernel.org; 
> user-mode-linux-devel@lists.sourceforge.net
> Subject: [uml-devel] [PATCH 19/19] UML - Make mconsole 
> version requestshappen in a process
> 
> Handling a host mconsole version request must be done in a 
> process context
> rather than interrupt context now that utsname information can be 
> process-specific rather than global.
> 
> Signed-off-by: Jeff Dike <jdike@addtoit.com>
> 
> Index: linux-2.6.16/arch/um/drivers/mconsole_user.c
> ===================================================================
> --- linux-2.6.16.orig/arch/um/drivers/mconsole_user.c
> +++ linux-2.6.16/arch/um/drivers/mconsole_user.c
> @@ -18,7 +18,12 @@
>  #include "umid.h"
>  
>  static struct mconsole_command commands[] = {
> -	{ "version", mconsole_version, MCONSOLE_INTR },
> +	/* With uts namespaces, uts information becomes 
> process-specific, so
> +	 * we need a process context.  If we try handling this 
> in interrupt
> +	 * context, we may hit an exiting process without a valid uts
> +	 * namespace.
> +	 */
> +	{ "version", mconsole_version, MCONSOLE_PROC },
>  	{ "halt", mconsole_halt, MCONSOLE_PROC },
>  	{ "reboot", mconsole_reboot, MCONSOLE_PROC },
>  	{ "config", mconsole_config, MCONSOLE_PROC },
> 
> 
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> User-mode-linux-devel@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
> 

Re: [uml-devel] [PATCH 19/19] UML - Make mconsole version requestshappen in a process

[Jeff Dike]

On Fri, Jul 07, 2006 at 08:31:50AM -0700, Brock, Anthony - NET wrote:
> I'm running UML on an SMP machine, but have never encountered the "hang"
> issue. Is this text still accurate? 

No, it's ancient history.  No one ever figured out what the problem was,
but it hasn't been seen in ages.

> Also, can this command still be used
>  to "wake up" a UML process? Is this still the recommended means for
> verifying that a UML process if running?

No, and no.

				Jeff

RE: [uml-devel] [PATCH 19/19] UML - Make mconsole versionrequestshappen in a process

[Brock, Anthony - NET]

> -----Original Message-----
> > Also, can this command still be used
> >  to "wake up" a UML process? Is this still the recommended means for
> > verifying that a UML process if running?
> 
> No, and no.

What is the recommended means for verifying that a UML process is
running?

Tony

Re: [uml-devel] [PATCH 19/19] UML - Make mconsole versionrequestshappen in a process

[Jeff Dike]

On Fri, Jul 07, 2006 at 10:07:25AM -0700, Brock, Anthony - NET wrote:
> What is the recommended means for verifying that a UML process is
> running?

Depends on what level of "running" you want to check for.  Ping will
tell you if the kernel can respond to interrupts.  mconsole version
(now) will tell you whether it can schedule processes.  mconsole sysrq
is another way to check that it is alive enough to respond to
interrupts.

				Jeff