From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Morton <akpm@osdl.org>
Subject: Re: kjournald() with DIO
Date: Thu, 15 Sep 2005 14:20:54 -0700
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To: Badari Pulavarty <pbadari@us.ibm.com>
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Badari Pulavarty <pbadari@us.ibm.com> wrote:
>
> Here is the race:
> 
> 
>  DIO Process				kjounald()
>  				journal_commit_transaction()
>        					  ...
>          			/* submited buffers for IO */
>          			/* Waiting for IO to complete */
>          			while (t_locked_list) {
>                 			  ...
>                	  		  get_bh(bh);
>                  	          if (buffer_locked(bh)) {
>                         		     spin_unlock(&journal->j_list_lock);
>                          	     wait_on_buffer(bh); 
>                                                                
>  						
>  invalidate_complete_page()
>          ..
>     ext3_releasepage()
>         journal_try_to_free_buffers()
>             journal_put_journal_head()
>                    __journal_try_to_free_buffer()
>                                   <--- freed jh
> 
>             try_to_free_buffers()
>                drop_buffers()
>                      if (buffer_busy(bh))
>                           goto failed;
>   <<--- returns EIO due to b_count

Right.   But there's still a race in there.

invalidate_complete_page() may still fail for these buffers.  The only
blocking it does is lock_buffer().  So if kjournald does:

	get_bh(bh);
	wait_on_bffer(bh);
				<- window
	put_bh(bh);

ext3_invalidatepage() may hit that unlocked, pinned buffer and fail to
release the page.

In that case, truncate_complete_page() will convert the apge into an
anonymous page (if it's mmapped).  If it's just a pagecache page then I
guess it'll be converted into a zero-ref page on the page LRU.

It's not possible for ext3_invalidatepage() to block until a buffer comes
unpinned.  We'd have to add additional stuff for that.  (bring back
wake_up_buffer(), for example).