On Fri, 28 Jan 2011, Eric Sandeen wrote:
> This is for the latest reported module unload oops in
> kernel.org bugzilla #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.
It looks good. Thanks for covering that Eric.
-Lukas
>
> Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
> ---
>
> Index: linux-2.6/fs/ext4/super.c
> ===================================================================
> --- linux-2.6.orig/fs/ext4/super.c
> +++ linux-2.6/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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