[Qemu-devel] [PATCH] spapr: fix xics_system_init() error path

[Qemu-devel] [PATCH] spapr: fix xics_system_init() error path

[Greg Kurz]

Commit 3d85885a1b1f3 tried to fix error handling, but it actually
went into the wrong direction by dropping the local Error *.

In the default KVM case, the rationale is to try the in-kernel XICS first,
and if not possible, to fallback to userland XICS. Passing errp everywhere
makes this fallback impossible if errp is &error_fatal (which happens to
be the case). And anyway, if the caller would pass a regular &local_err,
things would be worse: we could possibly pass an already set *errp to
error_setg() and crash, or return an error even in case of success.

So we definitely need a local Error * and only propagate it when we're
done with the fallback logic. This is what this patch does.

Signed-off-by: Greg Kurz <groug@kaod.org>
---
 hw/ppc/spapr.c |   22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index f59999daacfc..db0fb385d4e0 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -186,27 +186,33 @@ static int xics_max_server_number(sPAPRMachineState *spapr)
 static void xics_system_init(MachineState *machine, int nr_irqs, Error **errp)
 {
     sPAPRMachineState *spapr = SPAPR_MACHINE(machine);
+    Error *local_err = NULL;
 
     if (kvm_enabled()) {
         if (machine_kernel_irqchip_allowed(machine) &&
-            !xics_kvm_init(spapr, errp)) {
+            !xics_kvm_init(spapr, &local_err)) {
             spapr->icp_type = TYPE_KVM_ICP;
-            spapr->ics = spapr_ics_create(spapr, TYPE_ICS_KVM, nr_irqs, errp);
+            spapr->ics = spapr_ics_create(spapr, TYPE_ICS_KVM, nr_irqs,
+                                          &local_err);
         }
         if (machine_kernel_irqchip_required(machine) && !spapr->ics) {
-            error_prepend(errp, "kernel_irqchip requested but unavailable: ");
-            return;
+            error_prepend(&local_err,
+                          "kernel_irqchip requested but unavailable: ");
+            goto error;
         }
+        error_free(local_err);
+        local_err = NULL;
     }
 
     if (!spapr->ics) {
         xics_spapr_init(spapr);
         spapr->icp_type = TYPE_ICP;
-        spapr->ics = spapr_ics_create(spapr, TYPE_ICS_SIMPLE, nr_irqs, errp);
-        if (!spapr->ics) {
-            return;
-        }
+        spapr->ics = spapr_ics_create(spapr, TYPE_ICS_SIMPLE, nr_irqs,
+                                      &local_err);
     }
+
+error:
+    error_propagate(errp, local_err);
 }
 
 static int spapr_fixup_cpu_smt_dt(void *fdt, int offset, PowerPCCPU *cpu,

Re: [Qemu-devel] [PATCH] spapr: fix xics_system_init() error path

[David Gibson]

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On Fri, Jun 15, 2018 at 06:58:00PM +0200, Greg Kurz wrote:
> Commit 3d85885a1b1f3 tried to fix error handling, but it actually
> went into the wrong direction by dropping the local Error *.
> 
> In the default KVM case, the rationale is to try the in-kernel XICS first,
> and if not possible, to fallback to userland XICS. Passing errp everywhere
> makes this fallback impossible if errp is &error_fatal (which happens to
> be the case). And anyway, if the caller would pass a regular &local_err,
> things would be worse: we could possibly pass an already set *errp to
> error_setg() and crash, or return an error even in case of success.
> 
> So we definitely need a local Error * and only propagate it when we're
> done with the fallback logic. This is what this patch does.
> 
> Signed-off-by: Greg Kurz <groug@kaod.org>

Applied to ppc-for-3.0, thanks.

> ---
>  hw/ppc/spapr.c |   22 ++++++++++++++--------
>  1 file changed, 14 insertions(+), 8 deletions(-)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index f59999daacfc..db0fb385d4e0 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -186,27 +186,33 @@ static int xics_max_server_number(sPAPRMachineState *spapr)
>  static void xics_system_init(MachineState *machine, int nr_irqs, Error **errp)
>  {
>      sPAPRMachineState *spapr = SPAPR_MACHINE(machine);
> +    Error *local_err = NULL;
>  
>      if (kvm_enabled()) {
>          if (machine_kernel_irqchip_allowed(machine) &&
> -            !xics_kvm_init(spapr, errp)) {
> +            !xics_kvm_init(spapr, &local_err)) {
>              spapr->icp_type = TYPE_KVM_ICP;
> -            spapr->ics = spapr_ics_create(spapr, TYPE_ICS_KVM, nr_irqs, errp);
> +            spapr->ics = spapr_ics_create(spapr, TYPE_ICS_KVM, nr_irqs,
> +                                          &local_err);
>          }
>          if (machine_kernel_irqchip_required(machine) && !spapr->ics) {
> -            error_prepend(errp, "kernel_irqchip requested but unavailable: ");
> -            return;
> +            error_prepend(&local_err,
> +                          "kernel_irqchip requested but unavailable: ");
> +            goto error;
>          }
> +        error_free(local_err);
> +        local_err = NULL;
>      }
>  
>      if (!spapr->ics) {
>          xics_spapr_init(spapr);
>          spapr->icp_type = TYPE_ICP;
> -        spapr->ics = spapr_ics_create(spapr, TYPE_ICS_SIMPLE, nr_irqs, errp);
> -        if (!spapr->ics) {
> -            return;
> -        }
> +        spapr->ics = spapr_ics_create(spapr, TYPE_ICS_SIMPLE, nr_irqs,
> +                                      &local_err);
>      }
> +
> +error:
> +    error_propagate(errp, local_err);
>  }
>  
>  static int spapr_fixup_cpu_smt_dt(void *fdt, int offset, PowerPCCPU *cpu,
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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