[PATCH v2] xen: don't continue xenstore initialization in case of errors

[PATCH v2] xen: don't continue xenstore initialization in case of errors

[Stefano Stabellini]

From: Stefano Stabellini <stefano.stabellini@xilinx.com>

In case of errors in xenbus_init (e.g. missing xen_store_gfn parameter),
we goto out_error but we forget to reset xen_store_domain_type to
XS_UNKNOWN. As a consequence xenbus_probe_initcall and other initcalls
will still try to initialize xenstore resulting into a crash at boot.

[    2.479830] Call trace:
[    2.482314]  xb_init_comms+0x18/0x150
[    2.486354]  xs_init+0x34/0x138
[    2.489786]  xenbus_probe+0x4c/0x70
[    2.498432]  xenbus_probe_initcall+0x2c/0x7c
[    2.503944]  do_one_initcall+0x54/0x1b8
[    2.507358]  kernel_init_freeable+0x1ac/0x210
[    2.511617]  kernel_init+0x28/0x130
[    2.516112]  ret_from_fork+0x10/0x20

Cc: <Stable@vger.kernel.org>
Cc: jbeulich@suse.com
Signed-off-by: Stefano Stabellini <stefano.stabellini@xilinx.com>
---
Changes in v2:
- use return 0 for the success case
- remove err initializer as it is not useful any longer
---
 drivers/xen/xenbus/xenbus_probe.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
index bd003ca8acbe..5967aa937255 100644
--- a/drivers/xen/xenbus/xenbus_probe.c
+++ b/drivers/xen/xenbus/xenbus_probe.c
@@ -909,7 +909,7 @@ static struct notifier_block xenbus_resume_nb = {
 
 static int __init xenbus_init(void)
 {
-	int err = 0;
+	int err;
 	uint64_t v = 0;
 	xen_store_domain_type = XS_UNKNOWN;
 
@@ -983,8 +983,10 @@ static int __init xenbus_init(void)
 	 */
 	proc_create_mount_point("xen");
 #endif
+	return 0;
 
 out_error:
+	xen_store_domain_type = XS_UNKNOWN;
 	return err;
 }
 
-- 
2.25.1

Re: [PATCH v2] xen: don't continue xenstore initialization in case of errors

[Jan Beulich]

On 15.11.2021 23:27, Stefano Stabellini wrote:
> From: Stefano Stabellini <stefano.stabellini@xilinx.com>
> 
> In case of errors in xenbus_init (e.g. missing xen_store_gfn parameter),
> we goto out_error but we forget to reset xen_store_domain_type to
> XS_UNKNOWN. As a consequence xenbus_probe_initcall and other initcalls
> will still try to initialize xenstore resulting into a crash at boot.
> 
> [    2.479830] Call trace:
> [    2.482314]  xb_init_comms+0x18/0x150
> [    2.486354]  xs_init+0x34/0x138
> [    2.489786]  xenbus_probe+0x4c/0x70
> [    2.498432]  xenbus_probe_initcall+0x2c/0x7c
> [    2.503944]  do_one_initcall+0x54/0x1b8
> [    2.507358]  kernel_init_freeable+0x1ac/0x210
> [    2.511617]  kernel_init+0x28/0x130
> [    2.516112]  ret_from_fork+0x10/0x20
> 
> Cc: <Stable@vger.kernel.org>
> Cc: jbeulich@suse.com
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xilinx.com>

For the immediate purpose as described this looks okay, so
Reviewed-by: Jan Beulich <jbeulich@suse.com>

However, aren't there further pieces missing on this error patch:
- clearing of xenstored_ready in case it got set,
- rolling back xenstored_local_init() (XS_LOCAL) and xen_remap()
  (XS_HVM).
And shouldn't xs_init() failure when called from xenbus_probe()
also result in the driver not giving the appearance of being usable?

> --- a/drivers/xen/xenbus/xenbus_probe.c
> +++ b/drivers/xen/xenbus/xenbus_probe.c
> @@ -909,7 +909,7 @@ static struct notifier_block xenbus_resume_nb = {
>  
>  static int __init xenbus_init(void)
>  {
> -	int err = 0;
> +	int err;
>  	uint64_t v = 0;
>  	xen_store_domain_type = XS_UNKNOWN;
>  

Minor remark: You may want to take the opportunity and add the
missing blank line here to visually separate the assignment from
the declarations.

Jan

Re: [PATCH v2] xen: don't continue xenstore initialization in case of errors

[Stefano Stabellini]

On Tue, 16 Nov 2021, Jan Beulich wrote:
> On 15.11.2021 23:27, Stefano Stabellini wrote:
> > From: Stefano Stabellini <stefano.stabellini@xilinx.com>
> > 
> > In case of errors in xenbus_init (e.g. missing xen_store_gfn parameter),
> > we goto out_error but we forget to reset xen_store_domain_type to
> > XS_UNKNOWN. As a consequence xenbus_probe_initcall and other initcalls
> > will still try to initialize xenstore resulting into a crash at boot.
> > 
> > [    2.479830] Call trace:
> > [    2.482314]  xb_init_comms+0x18/0x150
> > [    2.486354]  xs_init+0x34/0x138
> > [    2.489786]  xenbus_probe+0x4c/0x70
> > [    2.498432]  xenbus_probe_initcall+0x2c/0x7c
> > [    2.503944]  do_one_initcall+0x54/0x1b8
> > [    2.507358]  kernel_init_freeable+0x1ac/0x210
> > [    2.511617]  kernel_init+0x28/0x130
> > [    2.516112]  ret_from_fork+0x10/0x20
> > 
> > Cc: <Stable@vger.kernel.org>
> > Cc: jbeulich@suse.com
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@xilinx.com>
> 
> For the immediate purpose as described this looks okay, so
> Reviewed-by: Jan Beulich <jbeulich@suse.com>

Thank you!


> However, aren't there further pieces missing on this error patch:
> - clearing of xenstored_ready in case it got set,
> - rolling back xenstored_local_init() (XS_LOCAL) and xen_remap()
>   (XS_HVM).
> And shouldn't xs_init() failure when called from xenbus_probe()
> also result in the driver not giving the appearance of being usable?

I prioritized this patch because I have a direct test case for this
issue and I can see that this patch solves it. But what you wrote is
true, and I can have a look in the following weeks.


> > --- a/drivers/xen/xenbus/xenbus_probe.c
> > +++ b/drivers/xen/xenbus/xenbus_probe.c
> > @@ -909,7 +909,7 @@ static struct notifier_block xenbus_resume_nb = {
> >  
> >  static int __init xenbus_init(void)
> >  {
> > -	int err = 0;
> > +	int err;
> >  	uint64_t v = 0;
> >  	xen_store_domain_type = XS_UNKNOWN;
> >  
> 
> Minor remark: You may want to take the opportunity and add the
> missing blank line here to visually separate the assignment from
> the declarations.
> 
> Jan
> 

Re: [PATCH v2] xen: don't continue xenstore initialization in case of errors

[Boris Ostrovsky]

On 11/15/21 5:27 PM, Stefano Stabellini wrote:
> From: Stefano Stabellini <stefano.stabellini@xilinx.com>
>
> In case of errors in xenbus_init (e.g. missing xen_store_gfn parameter),
> we goto out_error but we forget to reset xen_store_domain_type to
> XS_UNKNOWN. As a consequence xenbus_probe_initcall and other initcalls
> will still try to initialize xenstore resulting into a crash at boot.
>
> [    2.479830] Call trace:
> [    2.482314]  xb_init_comms+0x18/0x150
> [    2.486354]  xs_init+0x34/0x138
> [    2.489786]  xenbus_probe+0x4c/0x70
> [    2.498432]  xenbus_probe_initcall+0x2c/0x7c
> [    2.503944]  do_one_initcall+0x54/0x1b8
> [    2.507358]  kernel_init_freeable+0x1ac/0x210
> [    2.511617]  kernel_init+0x28/0x130
> [    2.516112]  ret_from_fork+0x10/0x20
>
> Cc: <Stable@vger.kernel.org>
> Cc: jbeulich@suse.com
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xilinx.com>



Applied to for-linus-5.16c


-boris