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SubjectRe: [3.1.6] Deadlock upon recursive call_usermodehelper_exec().
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Additional info. I added debug printk()

--- a/lib/kobject_uevent.c
+++ b/lib/kobject_uevent.c
@@ -305,8 +305,13 @@ int kobject_uevent_env(struct kobject *k
if (retval)
goto exit;

+ printk(KERN_INFO "*** Calling call_usermodehelper(\"%s\")\n",
+ argv[0]);
retval = call_usermodehelper(argv[0], argv,
env->envp, UMH_WAIT_EXEC);
+ printk(KERN_INFO
+ "*** Returned from call_usermodehelper(\"%s\")\n",
+ argv[0]);
}

exit:
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1435,7 +1435,14 @@ int search_binary_handler(struct linux_b
break; /* -ENOEXEC */
if (try)
break; /* -ENOEXEC */
+ printk(KERN_INFO
+ "*** Calling request_module(\"binfmt-%04x\")\n",
+ *(unsigned short *)(&bprm->buf[2]));
request_module("binfmt-%04x", *(unsigned short *)(&bprm->buf[2]));
+ printk(KERN_INFO
+ "*** Returned from "
+ "request_module(\"binfmt-%04x\")\n",
+ *(unsigned short *)(&bprm->buf[2]));
}
#else
break;
and got below output just before deadlock.

*** Calling call_usermodehelper("/sbin/hotplug")
*** Calling request_module("binfmt-0000")
So, this deadlock occurs when call_usermodehelper(UMH_WAIT_EXEC) is called and
request_module() is also called from search_binary_handler() when processing
call_usermodehelper(UMH_WAIT_EXEC).

This would not hanppen for normal condition, but 100% happens when the
userspace helper program is damaged.


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