Re: "resource: provide new functions to walk through resources" breaks UML

[Daniel Walter <sahne@0x90.at>]

----- Original Message -----
> From: "Vivek Goyal" <vgoyal@redhat.com>
> To: "Richard Weinberger" <richard@nod.at>
> Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, "user-mode-linux-devel"
> <user-mode-linux-devel@lists.sourceforge.net>, sahne@0x90.at
> Sent: Monday, August 11, 2014 7:44:01 PM
> Subject: Re: "resource: provide new functions to walk through resources" breaks UML
> 
> On Mon, Aug 11, 2014 at 02:25:56PM +0200, Richard Weinberger wrote:
> > Hi Vivek,
> > 
> > Am 11.08.2014 14:22, schrieb Vivek Goyal:
> > > On Sun, Aug 10, 2014 at 06:56:14PM +0200, Richard Weinberger
> > > wrote:
> > >> Hi Vivek,
> > >>
> > >> Daniel Walter reported that UML is currently broken.
> > >> The offending commit is:
> > >>
> > > 
> > > Hi Richard,
> > > 
> > > Thanks for pointing it out. I will look into it.
> > > 
> > > Would you have link to the report Daniel sent. I am interested in
> > > looking at backtrace.
> > 
> > he reported it on IRC to me.
> > 
> > Here is a backtrace:
> > RIP: 0033:[<0000000060039b9f>]
> > RSP: 0000000081459da0  EFLAGS: 00010202
> > RAX: 0000000000000000 RBX: 00000000219b3fff RCX: 000000006010d1d9
> > RDX: 0000000000000001 RSI: 00000000602dfb94 RDI: 0000000081459df8
> > RBP: 0000000081459de0 R08: 00000000601b59f4 R09: ffffffff0000ff00
> > R10: ffffffff0000ff00 R11: 0000000081459e88 R12: 0000000081459df8
> > R13: 00000000219b3fff R14: 00000000602dfb94 R15: 0000000000000000
> > Kernel panic - not syncing: Segfault with no mm
> > CPU: 0 PID: 1 Comm: swapper Not tainted 3.16.0-10454-g58d08e3 #13
> > Stack:
> >  00000000 000080d0 81459df0 219b3fff
> >  81459e70 6010d1d9 ffffffff 6033e010
> >  81459e50 6003a269 81459e30 00000000
> > Call Trace:
> >  [<6010d1d9>] ? kclist_add_private+0x0/0xe7
> >  [<6003a269>] walk_system_ram_range+0x61/0xb7
> >  [<6000e859>] ? proc_kcore_init+0x0/0xf1
> >  [<6010d574>] kcore_update_ram+0x4c/0x168
> >  [<6010d72e>] ? kclist_add+0x0/0x2e
> >  [<6000e943>] proc_kcore_init+0xea/0xf1
> >  [<6000e859>] ? proc_kcore_init+0x0/0xf1
> >  [<6000e859>] ? proc_kcore_init+0x0/0xf1
> >  [<600189f0>] do_one_initcall+0x13c/0x204
> >  [<6004ca46>] ? parse_args+0x1df/0x2e0
> >  [<6004c82d>] ? parameq+0x0/0x3a
> >  [<601b5990>] ? strcpy+0x0/0x18
> >  [<60001e1a>] kernel_init_freeable+0x240/0x31e
> >  [<6026f1c0>] kernel_init+0x12/0x148
> >  [<60019fad>] new_thread_handler+0x81/0xa3
> > 
> > RIP is at kernel/resource.c:66.
> 
> Hi Richard,
> 
> Can you please give the attached patch a try and see if it fixes the
> UML
> issue.
> 
> I noticed that previous code had a for() loop which will not execute
> if p was null. I have resorted back to same code now.
> 
> Thanks
> Vivek
> 
> 
> ---
>  kernel/resource.c |   11 ++++-------
>  1 file changed, 4 insertions(+), 7 deletions(-)
> 
> Index: linux-2.6/kernel/resource.c
> ===================================================================
> --- linux-2.6.orig/kernel/resource.c	2014-08-11 13:36:19.942423192
> -0400
> +++ linux-2.6/kernel/resource.c	2014-08-11 13:50:20.529387653 -0400
> @@ -351,15 +351,12 @@ static int find_next_iomem_res(struct re
>  	end = res->end;
>  	BUG_ON(start >= end);
>  
> -	read_lock(&resource_lock);
> -
> -	if (first_level_children_only) {
> -		p = iomem_resource.child;
> +	if (first_level_children_only)
>  		sibling_only = true;
> -	} else
> -		p = &iomem_resource;
>  
> -	while ((p = next_resource(p, sibling_only))) {
> +	read_lock(&resource_lock);
> +
> +	for (p = iomem_resource.child; p; p = next_resource(p,
> sibling_only)) {
>  		if (p->flags != res->flags)
>  			continue;
>  		if (name && strcmp(p->name, name))
> 

Looks good to me, tested it on top of current HEAD (c8d6637d0497d62093dbba0694c7b3a80b79bfe1)
for x86_64. 

Thanks,

daniel