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

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Date:   Tue, 16 Nov 2021 08:44:52 +0100
From:   Jan Beulich <jbeulich@...e.com>
To:     Stefano Stabellini <sstabellini@...nel.org>
Cc:     boris.ostrovsky@...cle.com, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org,
        Stefano Stabellini <stefano.stabellini@...inx.com>,
        Stable@...r.kernel.org, jgross@...e.com
Subject: Re: [PATCH v2] xen: don't continue xenstore initialization in case of
 errors

On 15.11.2021 23:27, Stefano Stabellini wrote:
> From: Stefano Stabellini <stefano.stabellini@...inx.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@...r.kernel.org>
> Cc: jbeulich@...e.com
> Signed-off-by: Stefano Stabellini <stefano.stabellini@...inx.com>

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