[RFC 4/4] {RFC} kmod.c: Add new call_usermodehelper_timeout() API

[Boaz Harrosh <bharrosh@panasas.com>]

In the blasphemous occasions that a the Kernel must call a user-mode program
half of the times it is more robust to not wait forever but limit the wait
for a specified timeout.

So add a new  call_usermodehelper_timeout() that implements that.
(Users of this new API will be added once this API is in mainline)

call_usermodehelper_fns() is added an extra timeout parameter which
is then implemented in call_usermodehelper_exec. The few users of
call_usermodehelper_fns() are also changed in this patch.

Since now the executing threads might come back after the waiting
thread has returned, do to a timeout. I used a simple kref pattern
to govern the life time of the subprocess_info struct.

Should some wait-forever callers today, be converted to this new
schema?

CC: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
---
 fs/exec.c                   |    2 +-
 include/linux/kmod.h        |   15 +++++++++++++--
 kernel/kmod.c               |   29 +++++++++++++++++++++--------
 kernel/sys.c                |    2 +-
 security/keys/request_key.c |    2 +-
 5 files changed, 37 insertions(+), 13 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 92ce83a..e696081 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -2197,7 +2197,7 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
 		}
 
 		retval = call_usermodehelper_fns(helper_argv[0], helper_argv,
-					NULL, UMH_WAIT_EXEC, umh_pipe_setup,
+					NULL, UMH_WAIT_EXEC, 0, umh_pipe_setup,
 					NULL, &cprm);
 		argv_free(helper_argv);
 		if (retval) {
diff --git a/include/linux/kmod.h b/include/linux/kmod.h
index 5a89c00..eccc3f5 100644
--- a/include/linux/kmod.h
+++ b/include/linux/kmod.h
@@ -25,6 +25,7 @@
 #include <linux/compiler.h>
 #include <linux/workqueue.h>
 #include <linux/sysctl.h>
+#include <linux/kref.h>
 
 #define KMOD_PATH_LEN 256
 
@@ -55,12 +56,14 @@ enum umh_wait {
 };
 
 struct subprocess_info {
+	struct kref kref;
 	struct work_struct work;
 	struct completion *complete;
 	char *path;
 	char **argv;
 	char **envp;
 	enum umh_wait wait;
+	unsigned long wait_timeout;
 	int retval;
 	int (*init)(struct subprocess_info *info, struct cred *new);
 	void (*cleanup)(struct subprocess_info *info);
@@ -69,14 +72,22 @@ struct subprocess_info {
 
 extern int
 call_usermodehelper_fns(char *path, char **argv, char **envp,
-			enum umh_wait wait,
+			enum umh_wait wait, unsigned long timeout,
 			int (*init)(struct subprocess_info *info, struct cred *new),
 			void (*cleanup)(struct subprocess_info *), void *data);
 
 static inline int
 call_usermodehelper(char *path, char **argv, char **envp, enum umh_wait wait)
 {
-	return call_usermodehelper_fns(path, argv, envp, wait,
+	return call_usermodehelper_fns(path, argv, envp, wait, 0,
+				       NULL, NULL, NULL);
+}
+
+static inline int
+call_usermodehelper_timeout(char *path, char **argv, char **envp,
+			    enum umh_wait wait, unsigned long timeout)
+{
+	return call_usermodehelper_fns(path, argv, envp, wait, timeout,
 				       NULL, NULL, NULL);
 }
 
diff --git a/kernel/kmod.c b/kernel/kmod.c
index 3cb7457..a72eefa 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -129,7 +129,7 @@ int __request_module(bool wait, const char *fmt, ...)
 	trace_module_request(module_name, wait, _RET_IP_);
 
 	ret = call_usermodehelper_fns(modprobe_path, argv, envp,
-			wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC,
+			wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC, 0,
 			NULL, NULL, NULL);
 
 	atomic_dec(&kmod_concurrent);
@@ -191,8 +191,11 @@ fail:
 	do_exit(0);
 }
 
-static void call_usermodehelper_freeinfo(struct subprocess_info *info)
+static void call_usermodehelper_freeinfo(struct kref *kref)
 {
+	struct subprocess_info *info =
+		container_of(kref, struct subprocess_info, kref);
+
 	if (info->cleanup)
 		(*info->cleanup)(info);
 	kfree(info);
@@ -235,6 +238,7 @@ static int wait_for_helper(void *data)
 	}
 
 	complete(sub_info->complete);
+	kref_put(&sub_info->kref, call_usermodehelper_freeinfo);
 	return 0;
 }
 
@@ -258,7 +262,8 @@ static void __call_usermodehelper(struct work_struct *work)
 
 	switch (wait) {
 	case UMH_NO_WAIT:
-		call_usermodehelper_freeinfo(sub_info);
+		kref_put(&sub_info->kref,  call_usermodehelper_freeinfo);
+		kref_put(&sub_info->kref,  call_usermodehelper_freeinfo);
 		break;
 
 	case UMH_WAIT_PROC:
@@ -269,6 +274,7 @@ static void __call_usermodehelper(struct work_struct *work)
 		if (pid < 0)
 			sub_info->retval = pid;
 		complete(sub_info->complete);
+		kref_put(&sub_info->kref, call_usermodehelper_freeinfo);
 	}
 }
 
@@ -387,6 +393,7 @@ struct subprocess_info *call_usermodehelper_setup(char *path, char **argv,
 	if (!sub_info)
 		goto out;
 
+	kref_init(&sub_info->kref);
 	INIT_WORK(&sub_info->work, __call_usermodehelper);
 	sub_info->path = path;
 	sub_info->argv = argv;
@@ -452,22 +459,27 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info,
 
 	sub_info->complete = &done;
 	sub_info->wait = wait;
+	if (!sub_info->wait_timeout)
+		sub_info->wait_timeout = MAX_SCHEDULE_TIMEOUT;
 
+	/* Balanced in __call_usermodehelper or wait_for_helper */
+	kref_get(&sub_info->kref);
 	queue_work(khelper_wq, &sub_info->work);
 	if (wait == UMH_NO_WAIT)	/* task has freed sub_info */
 		goto unlock;
-	wait_for_completion(&done);
-	retval = sub_info->retval;
-
+	if (likely(wait_for_completion_timeout(&done, sub_info->wait_timeout)))
+		retval = sub_info->retval;
+	else
+		retval = -ETIMEDOUT;
 out:
-	call_usermodehelper_freeinfo(sub_info);
+	kref_put(&sub_info->kref, call_usermodehelper_freeinfo);
 unlock:
 	helper_unlock();
 	return retval;
 }
 
 int call_usermodehelper_fns(char *path, char **argv, char **envp,
-			enum umh_wait wait,
+			enum umh_wait wait, unsigned long timeout,
 			int (*init)(struct subprocess_info *info, struct cred *new),
 			void (*cleanup)(struct subprocess_info *), void *data)
 {
@@ -480,6 +492,7 @@ int call_usermodehelper_fns(char *path, char **argv, char **envp,
 		return -ENOMEM;
 
 	call_usermodehelper_setfns(info, init, cleanup, data);
+	info->wait_timeout = timeout;
 
 	return call_usermodehelper_exec(info, wait);
 }
diff --git a/kernel/sys.c b/kernel/sys.c
index 9947fb0..a9079d1 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2013,7 +2013,7 @@ int orderly_poweroff(bool force)
 		goto out;
 	}
 
-	ret = call_usermodehelper_fns(argv[0], argv, envp, UMH_NO_WAIT,
+	ret = call_usermodehelper_fns(argv[0], argv, envp, UMH_NO_WAIT, 0,
 				      NULL, argv_cleanup, NULL);
 
   out:
diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index b8cc38c..28050ea 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -93,7 +93,7 @@ static void umh_keys_cleanup(struct subprocess_info *info)
 static int call_usermodehelper_keys(char *path, char **argv, char **envp,
 			 struct key *session_keyring, enum umh_wait wait)
 {
-	return call_usermodehelper_fns(path, argv, envp, wait,
+	return call_usermodehelper_fns(path, argv, envp, wait, 0,
 				       umh_keys_init, umh_keys_cleanup,
 				       key_get(session_keyring));
 }
-- 
1.7.6.2