jbd: check for error returned by kthread_create on creating journal thread

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.

(akpm: JBD should be converted fully to the kthread API: kthread_should_stop()
and kthread_stop()).

Cc: <linux-ext4@vger.kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 18 insertions, 8 deletions

diff --git a/fs/jbd/journal.c b/fs/jbd/journal.c
index e1eb7e999ae8..46fe7439fb91 100644
--- a/fs/jbd/journal.c
+++ b/fs/jbd/journal.c
@@ -210,10 +210,16 @@ 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)
@@ -839,8 +845,7 @@ static int journal_reset(journal_t *journal)
 
         /* 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);
 }
 
 /**
diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 6b3158ec9e2c..78d63b818f0b 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -210,10 +210,16 @@ 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)
@@ -839,8 +845,7 @@ static int journal_reset(journal_t *journal)
 
         /* 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);
 }
 
 /**