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

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Date:   Tue, 16 Nov 2021 12:41:12 -0800 (PST)
From:   Stefano Stabellini <sstabellini@...nel.org>
To:     Jan Beulich <jbeulich@...e.com>
cc:     Stefano Stabellini <sstabellini@...nel.org>,
        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 Tue, 16 Nov 2021, Jan Beulich wrote:
> 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>

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
>