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

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Date:	Mon, 11 Aug 2014 14:44:01 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Richard Weinberger <richard@....at>
Cc:	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	user-mode-linux-devel <user-mode-linux-devel@...ts.sourceforge.net>,
	sahne@...0.at
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))
--
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