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Subject[132/272] ext4: fix panic on module unload when stopping lazyinit thread
2.6.37-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Eric Sandeen <sandeen@redhat.com>

commit 8f1f745331c1b560f53c0d60e55a4f4f43f7cce5 upstream.

https://bugzilla.kernel.org/show_bug.cgi?id=27652

If the lazyinit thread is running, the teardown function
ext4_destroy_lazyinit_thread() has problems:

ext4_clear_request_list();
while (ext4_li_info->li_task) {
wake_up(&ext4_li_info->li_wait_daemon);
wait_event(ext4_li_info->li_wait_task,
ext4_li_info->li_task == NULL);
}

Clearing the request list will cause the thread to exit and free
ext4_li_info, so then we're waiting on something which is getting
freed.

Fix this up by making the thread respond to kthread_stop, and exit,
without the need to wait for that exit in some other homegrown way.

Reported-and-Tested-by: Tao Ma <boyu.mt@taobao.com>
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
fs/ext4/super.c | 27 ++++++++++++++-------------
1 file changed, 14 insertions(+), 13 deletions(-)

--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -77,6 +77,7 @@ static struct dentry *ext4_mount(struct
const char *dev_name, void *data);
static void ext4_destroy_lazyinit_thread(void);
static void ext4_unregister_li_request(struct super_block *sb);
+static void ext4_clear_request_list(void);

#if !defined(CONFIG_EXT3_FS) && !defined(CONFIG_EXT3_FS_MODULE) && defined(CONFIG_EXT4_USE_FOR_EXT23)
static struct file_system_type ext3_fs_type = {
@@ -2704,6 +2705,8 @@ static void ext4_unregister_li_request(s
mutex_unlock(&ext4_li_info->li_list_mtx);
}

+static struct task_struct *ext4_lazyinit_task;
+
/*
* This is the function where ext4lazyinit thread lives. It walks
* through the request list searching for next scheduled filesystem.
@@ -2772,6 +2775,10 @@ cont_thread:
if (time_before(jiffies, next_wakeup))
schedule();
finish_wait(&eli->li_wait_daemon, &wait);
+ if (kthread_should_stop()) {
+ ext4_clear_request_list();
+ goto exit_thread;
+ }
}

exit_thread:
@@ -2796,6 +2803,7 @@ exit_thread:
wake_up(&eli->li_wait_task);

kfree(ext4_li_info);
+ ext4_lazyinit_task = NULL;
ext4_li_info = NULL;
mutex_unlock(&ext4_li_mtx);

@@ -2818,11 +2826,10 @@ static void ext4_clear_request_list(void

static int ext4_run_lazyinit_thread(void)
{
- struct task_struct *t;
-
- t = kthread_run(ext4_lazyinit_thread, ext4_li_info, "ext4lazyinit");
- if (IS_ERR(t)) {
- int err = PTR_ERR(t);
+ ext4_lazyinit_task = kthread_run(ext4_lazyinit_thread,
+ ext4_li_info, "ext4lazyinit");
+ if (IS_ERR(ext4_lazyinit_task)) {
+ int err = PTR_ERR(ext4_lazyinit_task);
ext4_clear_request_list();
del_timer_sync(&ext4_li_info->li_timer);
kfree(ext4_li_info);
@@ -2973,16 +2980,10 @@ static void ext4_destroy_lazyinit_thread
* If thread exited earlier
* there's nothing to be done.
*/
- if (!ext4_li_info)
+ if (!ext4_li_info || !ext4_lazyinit_task)
return;

- ext4_clear_request_list();
-
- while (ext4_li_info->li_task) {
- wake_up(&ext4_li_info->li_wait_daemon);
- wait_event(ext4_li_info->li_wait_task,
- ext4_li_info->li_task == NULL);
- }
+ kthread_stop(ext4_lazyinit_task);
}

static int ext4_fill_super(struct super_block *sb, void *data, int silent)



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