From 034f1b331e2c152e8e8954d715fa9a84f7b48d64 Mon Sep 17 00:00:00 2001
From: Brian Behlendorf <behlendorf1@llnl.gov>
Date: Tue, 18 Dec 2012 17:02:27 -0800
Subject: [PATCH] Fix spl_kmem_init_kallsyms_lookup() panic

Due to I/O buffering the helper may return successfully before
the proc handler has a chance to execute.  To catch this case
wait up to 1 second to verify spl_kallsyms_lookup_name_fn was
updated to a non SYMBOL_POISON value.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes zfsonlinux/zfs#699
Closes zfsonlinux/zfs#859
---
 include/linux/kallsyms_compat.h |  1 +
 module/spl/spl-generic.c        | 19 +++++++++++++++++++
 module/spl/spl-proc.c           |  2 ++
 3 files changed, 22 insertions(+)

diff --git a/include/linux/kallsyms_compat.h b/include/linux/kallsyms_compat.h
index 34c45ea3..fbe33e8e 100644
--- a/include/linux/kallsyms_compat.h
+++ b/include/linux/kallsyms_compat.h
@@ -34,6 +34,7 @@
 
 #else
 
+extern wait_queue_head_t spl_kallsyms_lookup_name_waitq;
 typedef unsigned long (*kallsyms_lookup_name_t)(const char *);
 extern kallsyms_lookup_name_t spl_kallsyms_lookup_name_fn;
 #define spl_kallsyms_lookup_name(name) spl_kallsyms_lookup_name_fn(name)
diff --git a/module/spl/spl-generic.c b/module/spl/spl-generic.c
index cc276645..22ea5078 100644
--- a/module/spl/spl-generic.c
+++ b/module/spl/spl-generic.c
@@ -64,6 +64,7 @@ proc_t p0 = { 0 };
 EXPORT_SYMBOL(p0);
 
 #ifndef HAVE_KALLSYMS_LOOKUP_NAME
+DECLARE_WAIT_QUEUE_HEAD(spl_kallsyms_lookup_name_waitq);
 kallsyms_lookup_name_t spl_kallsyms_lookup_name_fn = SYMBOL_POISON;
 #endif
 
@@ -607,6 +608,24 @@ set_kallsyms_lookup_name(void)
 	int rc;
 
 	rc = call_usermodehelper(argv[0], argv, envp, 1);
+
+	/*
+	 * Due to I/O buffering the helper may return successfully before
+	 * the proc handler has a chance to execute.  To catch this case
+	 * wait up to 1 second to verify spl_kallsyms_lookup_name_fn was
+	 * updated to a non SYMBOL_POISON value.
+	 */
+	if (rc == 0) {
+		rc = wait_event_timeout(spl_kallsyms_lookup_name_waitq,
+		    spl_kallsyms_lookup_name_fn != SYMBOL_POISON, HZ);
+		if (rc == 0)
+			rc = -ETIMEDOUT;
+		else if (spl_kallsyms_lookup_name_fn == SYMBOL_POISON)
+			rc = -EFAULT;
+		else
+			rc = 0;
+	}
+
 	if (rc)
 		printk("SPL: Failed user helper '%s %s %s', rc = %d\n",
 		       argv[0], argv[1], argv[2], rc);
diff --git a/module/spl/spl-proc.c b/module/spl/spl-proc.c
index 152abff7..2fb29543 100644
--- a/module/spl/spl-proc.c
+++ b/module/spl/spl-proc.c
@@ -546,6 +546,8 @@ SPL_PROC_HANDLER(proc_dokallsyms_lookup_name)
 
                 spl_kallsyms_lookup_name_fn =
 			(kallsyms_lookup_name_t)simple_strtoul(str, &end, 16);
+		wake_up(&spl_kallsyms_lookup_name_waitq);
+
 		if (str == end)
 			SRETURN(-EINVAL);