[PATCH] Check for error returned by kthread_create on creating journal thread

[Pavel Emelianov]

If the thread failed to create the subsequent wait_event
will hang forever.

This is likely to happen if kernel hits max_threads limit.

Will be critical for virtualization systems that limit the
number of tasks and kernel memory usage within the container.

--- ./fs/jbd/journal.c.jbdthreads       2007-04-16 11:17:36.000000000 +0400
+++ ./fs/jbd/journal.c  2007-04-16 11:30:09.000000000 +0400
@@ -211,10 +211,16 @@ end_loop:
        return 0;
 }
 
-static void journal_start_thread(journal_t *journal)
+static int journal_start_thread(journal_t *journal)
 {
-       kthread_run(kjournald, journal, "kjournald");
+       struct task_struct *t;
+
+       t = kthread_run(kjournald, journal, "kjournald");
+       if (IS_ERR(t))
+               return PTR_ERR(t);
+
        wait_event(journal->j_wait_done_commit, journal->j_task != 0);
+       return 0;
 }
 
 static void journal_kill_thread(journal_t *journal)
@@ -840,8 +846,7 @@ static int journal_reset(journal_t *jour
 
        /* Add the dynamic fields and write it to disk. */
        journal_update_superblock(journal, 1);
-       journal_start_thread(journal);
-       return 0;
+       return journal_start_thread(journal);
 }
 
 /**
--- ./fs/jbd2/journal.c.jbdthreads      2007-04-16 11:17:36.000000000 +0400
+++ ./fs/jbd2/journal.c 2007-04-16 11:27:45.000000000 +0400
@@ -211,10 +211,16 @@ end_loop:
        return 0;
 }
 
-static void jbd2_journal_start_thread(journal_t *journal)
+static int jbd2_journal_start_thread(journal_t *journal)
 {
-       kthread_run(kjournald2, journal, "kjournald2");
+       struct task_struct *t;
+
+       t = kthread_run(kjournald2, journal, "kjournald2");
+       if (IS_ERR(t))
+               return PTR_ERR(t);
+
        wait_event(journal->j_wait_done_commit, journal->j_task != 0);
+       return 0;
 }
 
 static void journal_kill_thread(journal_t *journal)
@@ -840,8 +846,7 @@ static int journal_reset(journal_t *jour
 
        /* Add the dynamic fields and write it to disk. */
        jbd2_journal_update_superblock(journal, 1);
-       jbd2_journal_start_thread(journal);
-       return 0;
+       return jbd2_journal_start_thread(journal);
 }
 
 /**