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Re: [PATCH v2 18/29] hw/vfio/ap: Fix missing ERRP_GUARD() for error_prep

From: Cédric Le Goater
Subject: Re: [PATCH v2 18/29] hw/vfio/ap: Fix missing ERRP_GUARD() for error_prepend()
Date: Mon, 11 Mar 2024 08:42:54 +0100
User-agent: Mozilla Thunderbird

On 3/11/24 04:38, Zhao Liu wrote:
From: Zhao Liu <zhao1.liu@intel.com>

As the comment in qapi/error, passing @errp to error_prepend() requires

* = Why, when and how to use ERRP_GUARD() =
* Without ERRP_GUARD(), use of the @errp parameter is restricted:
* - It should not be passed to error_prepend(), error_vprepend() or
*   error_append_hint(), because that doesn't work with &error_fatal.
* ERRP_GUARD() lifts these restrictions.
* To use ERRP_GUARD(), add it right at the beginning of the function.
* @errp can then be used without worrying about the argument being
* NULL or &error_fatal.

ERRP_GUARD() could avoid the case when @errp is &error_fatal, the user
can't see this additional information, because exit() happens in
error_setg earlier than information is added [1].

The vfio_ap_realize() passes @errp to error_prepend(), and as a
DeviceClass.realize method, there are too many possible callers to check
the impact of this defect; it may or may not be harmless. Thus it is
necessary to protect @errp with ERRP_GUARD().

To avoid the issue like [1] said, add missing ERRP_GUARD() at the
beginning of this function.

[1]: Issue description in the commit message of commit ae7c80a7bd73
      ("error: New macro ERRP_GUARD()").

Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: "Cédric Le Goater" <clg@redhat.com>
Cc: Tony Krowiak <akrowiak@linux.ibm.com>
Cc: Halil Pasic <pasic@linux.ibm.com>
Cc: Jason Herne <jjherne@linux.ibm.com>
Cc: Thomas Huth <thuth@redhat.com>
Cc: qemu-s390x@nongnu.org
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>

Reviewed-by: Cédric Le Goater <clg@redhat.com>



v2: Use Markus' sentence to polish commit message. (Markus)
  hw/vfio/ap.c | 1 +
  1 file changed, 1 insertion(+)

diff --git a/hw/vfio/ap.c b/hw/vfio/ap.c
index e157aa1ff79c..7c4caa593863 100644
--- a/hw/vfio/ap.c
+++ b/hw/vfio/ap.c
@@ -155,6 +155,7 @@ static void vfio_ap_unregister_irq_notifier(VFIOAPDevice 
static void vfio_ap_realize(DeviceState *dev, Error **errp)
+    ERRP_GUARD();
      int ret;
      Error *err = NULL;
      VFIOAPDevice *vapdev = VFIO_AP_DEVICE(dev);

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