[PATCH] kexec/fs2dt.c: wrong dt node fix

[PATCH] kexec/fs2dt.c: wrong dt node fix

[Dave Young]

There is a report for ppc64le kexec fail in below Fedora 23 bug:
https://bugzilla.redhat.com/show_bug.cgi?id=1310495

2nd kernel hangs early because of a regression caused by below commit:
commit 68262155d8c661586b809bc5301a7dff1c378137
Author: Andrew Jones <drjones@redhat.com>
Date:   Fri Nov 20 12:31:53 2015 -0500

    kexec/fs2dt: cleanup pathname
    
    putnode() will add the trailing '/', avoid having two. Also
    pathstart is unused, get rid of it.
    
    Signed-off-by: Andrew Jones <drjones@redhat.com>
    Signed-off-by: Simon Horman <horms@verge.net.au>

The actual purpose of the commit is to avoid double slash in pathname.
But unfortunately in function putnode() we have below magics to get the node
name:
	basename = strrchr(pathname,'/') + 1;
	...
	strcpy((void *)dt, *basename ? basename : "");
	...
	strcat(pathname, "/");

We treat none zero basename as a node name, then concat a slash to open the
directory for later property handling.
pathname originally was "/proc/device-tree/" so for the first run of putnode
it will cause double slashes. With the commit above mentioned there are no
double slashes but we will copy "device-tree" to dt. Thus kexec kernel is not
happy..

Instead let's fix it by only concating slash when the basenanme is not empty
and restore the initial value of pathname as "/proc/device-tree/"

Signed-off-by: Dave Young <dyoung@redhat.com>
---
 kexec/fs2dt.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- kexec-tools.orig/kexec/fs2dt.c
+++ kexec-tools/kexec/fs2dt.c
@@ -577,7 +577,8 @@ static void putnode(void)
 	strcpy((void *)dt, *basename ? basename : "");
 	dt += ((plen + 4)/4);
 
-	strcat(pathname, "/");
+	if (*basename)
+		strcat(pathname, "/");
 	dn = pathname + strlen(pathname);
 
 	putprops(dn, namelist, numlist);
@@ -804,7 +805,7 @@ static void add_boot_block(char **bufp,
 
 void create_flatten_tree(char **bufp, off_t *sizep, const char *cmdline)
 {
-	strcpy(pathname, "/proc/device-tree");
+	strcpy(pathname, "/proc/device-tree/");
 
 	dt_cur_size = INIT_TREE_WORDS;
 	dt_base = malloc(dt_cur_size*4);

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Re: [PATCH] kexec/fs2dt.c: wrong dt node fix

[Dave Young]

Simon,

Oops, the patchlog need a revise since I tested a local branch with latest
upstream kexec-tools, but it is not necessary in F23.

But the code change is still valid to me, will repost with an updated
patch descriptioin.

On 02/26/16 at 11:43am, Dave Young wrote:
> There is a report for ppc64le kexec fail in below Fedora 23 bug:
> https://bugzilla.redhat.com/show_bug.cgi?id=1310495
> 
> 2nd kernel hangs early because of a regression caused by below commit:
> commit 68262155d8c661586b809bc5301a7dff1c378137
> Author: Andrew Jones <drjones@redhat.com>
> Date:   Fri Nov 20 12:31:53 2015 -0500
> 
>     kexec/fs2dt: cleanup pathname
>     
>     putnode() will add the trailing '/', avoid having two. Also
>     pathstart is unused, get rid of it.
>     
>     Signed-off-by: Andrew Jones <drjones@redhat.com>
>     Signed-off-by: Simon Horman <horms@verge.net.au>
> 
> The actual purpose of the commit is to avoid double slash in pathname.
> But unfortunately in function putnode() we have below magics to get the node
> name:
> 	basename = strrchr(pathname,'/') + 1;
> 	...
> 	strcpy((void *)dt, *basename ? basename : "");
> 	...
> 	strcat(pathname, "/");
> 
> We treat none zero basename as a node name, then concat a slash to open the
> directory for later property handling.
> pathname originally was "/proc/device-tree/" so for the first run of putnode
> it will cause double slashes. With the commit above mentioned there are no
> double slashes but we will copy "device-tree" to dt. Thus kexec kernel is not
> happy..
> 
> Instead let's fix it by only concating slash when the basenanme is not empty
> and restore the initial value of pathname as "/proc/device-tree/"
> 
> Signed-off-by: Dave Young <dyoung@redhat.com>
> ---
>  kexec/fs2dt.c |    5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> --- kexec-tools.orig/kexec/fs2dt.c
> +++ kexec-tools/kexec/fs2dt.c
> @@ -577,7 +577,8 @@ static void putnode(void)
>  	strcpy((void *)dt, *basename ? basename : "");
>  	dt += ((plen + 4)/4);
>  
> -	strcat(pathname, "/");
> +	if (*basename)
> +		strcat(pathname, "/");
>  	dn = pathname + strlen(pathname);
>  
>  	putprops(dn, namelist, numlist);
> @@ -804,7 +805,7 @@ static void add_boot_block(char **bufp,
>  
>  void create_flatten_tree(char **bufp, off_t *sizep, const char *cmdline)
>  {
> -	strcpy(pathname, "/proc/device-tree");
> +	strcpy(pathname, "/proc/device-tree/");
>  
>  	dt_cur_size = INIT_TREE_WORDS;
>  	dt_base = malloc(dt_cur_size*4);

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