[PATCH 0/2] xen: An error handling fix

[PATCH 0/2] xen: An error handling fix

[Markus Armbruster]

Question to reviewers: should PATCH 2 downgrade to warning, to info,
or delete the report entirely?

Markus Armbruster (2):
  hw/xen: Fix xen_bus_realize() error handling
  hw/xen: Downgrade a xen_bus_realize() non-error to warning

 hw/xen/xen-bus.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

-- 
2.48.1

[PATCH 1/2] hw/xen: Fix xen_bus_realize() error handling

[Markus Armbruster]

The Error ** argument must be NULL, &error_abort, &error_fatal, or a
pointer to a variable containing NULL.  Passing an argument of the
latter kind twice without clearing it in between is wrong: if the
first call sets an error, it no longer points to NULL for the second
call.

xen_bus_realize() is wrong that way: it passes &local_err to
xs_node_watch() in a loop.  If this fails in more than one iteration,
it can trip error_setv()'s assertion.

Fix by clearing @local_err.

Fixes: c4583c8c394e (xen-bus: reduce scope of backend watch)
Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 hw/xen/xen-bus.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/hw/xen/xen-bus.c b/hw/xen/xen-bus.c
index 8260f1e1bb..2aacc1436f 100644
--- a/hw/xen/xen-bus.c
+++ b/hw/xen/xen-bus.c
@@ -357,6 +357,7 @@ static void xen_bus_realize(BusState *bus, Error **errp)
             error_reportf_err(local_err,
                               "failed to set up '%s' enumeration watch: ",
                               type[i]);
+            local_err = NULL;
         }
 
         g_free(node);
-- 
2.48.1

[PATCH 2/2] hw/xen: Downgrade a xen_bus_realize() non-error to warning

[Markus Armbruster]

xen_bus_realize() reports a failure to set up a watch as error, but it
doesn't treat it as one: it simply continues.  Report a warning
instead.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 hw/xen/xen-bus.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/hw/xen/xen-bus.c b/hw/xen/xen-bus.c
index 2aacc1436f..f808a01813 100644
--- a/hw/xen/xen-bus.c
+++ b/hw/xen/xen-bus.c
@@ -353,10 +353,9 @@ static void xen_bus_realize(BusState *bus, Error **errp)
             xs_node_watch(xenbus->xsh, node, key, xen_bus_backend_changed,
                           xenbus, &local_err);
         if (local_err) {
-            /* This need not be treated as a hard error so don't propagate */
-            error_reportf_err(local_err,
-                              "failed to set up '%s' enumeration watch: ",
-                              type[i]);
+            warn_reportf_err(local_err,
+                             "failed to set up '%s' enumeration watch: ",
+                             type[i]);
             local_err = NULL;
         }
 
-- 
2.48.1

Re: [PATCH 1/2] hw/xen: Fix xen_bus_realize() error handling

[Stefano Stabellini]

On Fri, 14 Mar 2025, Markus Armbruster wrote:
> The Error ** argument must be NULL, &error_abort, &error_fatal, or a
> pointer to a variable containing NULL.  Passing an argument of the
> latter kind twice without clearing it in between is wrong: if the
> first call sets an error, it no longer points to NULL for the second
> call.
> 
> xen_bus_realize() is wrong that way: it passes &local_err to
> xs_node_watch() in a loop.  If this fails in more than one iteration,
> it can trip error_setv()'s assertion.
> 
> Fix by clearing @local_err.
> 
> Fixes: c4583c8c394e (xen-bus: reduce scope of backend watch)
> Signed-off-by: Markus Armbruster <armbru@redhat.com>

Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>


> ---
>  hw/xen/xen-bus.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/hw/xen/xen-bus.c b/hw/xen/xen-bus.c
> index 8260f1e1bb..2aacc1436f 100644
> --- a/hw/xen/xen-bus.c
> +++ b/hw/xen/xen-bus.c
> @@ -357,6 +357,7 @@ static void xen_bus_realize(BusState *bus, Error **errp)
>              error_reportf_err(local_err,
>                                "failed to set up '%s' enumeration watch: ",
>                                type[i]);
> +            local_err = NULL;
>          }
>  
>          g_free(node);
> -- 
> 2.48.1
> 

Re: [PATCH 2/2] hw/xen: Downgrade a xen_bus_realize() non-error to warning

[Stefano Stabellini]

On Fri, 14 Mar 2025, Markus Armbruster wrote:
> xen_bus_realize() reports a failure to set up a watch as error, but it
> doesn't treat it as one: it simply continues.  Report a warning
> instead.
> 
> Signed-off-by: Markus Armbruster <armbru@redhat.com>

Acked-by: Stefano Stabellini <sstabellini@kernel.org>


> ---
>  hw/xen/xen-bus.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/xen/xen-bus.c b/hw/xen/xen-bus.c
> index 2aacc1436f..f808a01813 100644
> --- a/hw/xen/xen-bus.c
> +++ b/hw/xen/xen-bus.c
> @@ -353,10 +353,9 @@ static void xen_bus_realize(BusState *bus, Error **errp)
>              xs_node_watch(xenbus->xsh, node, key, xen_bus_backend_changed,
>                            xenbus, &local_err);
>          if (local_err) {
> -            /* This need not be treated as a hard error so don't propagate */
> -            error_reportf_err(local_err,
> -                              "failed to set up '%s' enumeration watch: ",
> -                              type[i]);
> +            warn_reportf_err(local_err,
> +                             "failed to set up '%s' enumeration watch: ",
> +                             type[i]);
>              local_err = NULL;
>          }
>  
> -- 
> 2.48.1
> 

Re: [PATCH 0/2] xen: An error handling fix

[Markus Armbruster]

Queued for 10.0.