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SubjectRe: [PATCH] call_usermodehelper hang
Andrew Morton wrote:
> Greg KH <greg@kroah.com> 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);
_
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