linux-ext4 - Re: [PATCH] ext4: fix panic on module unload when stopping lazyinit thread

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Date:	Mon, 31 Jan 2011 14:08:44 +0100 (CET)
From:	Lukas Czerner <lczerner@...hat.com>
To:	Eric Sandeen <sandeen@...hat.com>
cc:	ext4 development <linux-ext4@...r.kernel.org>,
	Lukáš Czerner <lczerner@...hat.com>
Subject: Re: [PATCH] ext4: fix panic on module unload when stopping lazyinit
 thread

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@...hat.com>
> ---
> 
> 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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