Re: [PATCH] call_usermodehelper hang

[Brian King]

Andrew Morton wrote:
> Greg KH <greg@xxxxxxxxx> wrote:
>
> > > The deadlock opportunity occurs during the call_usermodehelper() handoff to
> >
> > > keventd, which is synchronous.
> > > 
> > > 2-3 years back I did have a call_usermodehelper() which was fully async. 
> > > It was pretty unpleasant because of the need to atomically allocate
> > > arbitrary amounts of memory to hold the argv[] and endp[] arrays, to pass
> > > them between a couple of threads and to then correctly free it all up
> > > again.
> >
> > Ok, you've convinced me of the mess that would cause.  So what should we
> > do to help fix this?  Serialize call_usermodehelper()?
>
>
> May as well bring back call_usermodehelper_async() I guess.
>
>
> There are two patches here, and they are totally untested...

I loaded the patches on my ppc64 box and they worked fine after I fixed a compile
bug. The attached patch fixes the compile bug and changes the call_usermodehelper
call in kset_hotplug to call_usermodehelper_async.

-Brian




--
Brian King
eServer Storage I/O
IBM Linux Technology Center

Fixes a compile error in call_usermodehelper_async and changes kset_hotplug 
to use call_usermodehelper_async, since it is called with a semaphore held,
which can result in a deadlock.


---


diff -puN kernel/kmod.c~call_usermodehelper_kobject kernel/kmod.c
--- linux-2.6.5/kernel/kmod.c~call_usermodehelper_kobject	Mon Apr 12 08:27:20 2004
+++ linux-2.6.5-bjking1/kernel/kmod.c	Mon Apr 12 08:27:44 2004
@@ -296,7 +296,7 @@ int call_usermodehelper_async(char *path
 {
 	struct subprocess_info *sub_info;
 
-	if (system_state != SYSTEM_RUNNING)
+	if (!system_running)
 		return -EBUSY;
 	if (path[0] == '\0')
 		goto out;
diff -puN lib/kobject.c~call_usermodehelper_kobject lib/kobject.c
--- linux-2.6.5/lib/kobject.c~call_usermodehelper_kobject	Mon Apr 12 08:28:07 2004
+++ linux-2.6.5-bjking1/lib/kobject.c	Mon Apr 12 08:28:28 2004
@@ -187,7 +187,7 @@ static void kset_hotplug(const char *act
 
 	pr_debug ("%s: %s %s %s %s %s %s %s\n", __FUNCTION__, argv[0], argv[1],
 		  envp[0], envp[1], envp[2], envp[3], envp[4]);
-	retval = call_usermodehelper (argv[0], argv, envp, 0);
+	retval = call_usermodehelper_async (argv[0], argv, envp, GFP_KERNEL);
 	if (retval)
 		pr_debug ("%s - call_usermodehelper returned %d\n",
 			  __FUNCTION__, retval);

_