linux-ext4 - Re: [PATCH] jbd2: Fix oops in jbd2_journal_remove_journal

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Message-ID: <20110606141630.GK7180@thunk.org>
Date:	Mon, 6 Jun 2011 10:16:30 -0400
From:	Ted Ts'o <tytso@....edu>
To:	Jan Kara <jack@...e.cz>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH] jbd2: Fix oops in jbd2_journal_remove_journal_head()

On Mon, May 30, 2011 at 05:12:58PM +0200, Jan Kara wrote:
>  /*
> - * For the unlocked version of this call, also make sure that any
> - * hanging journal_head is cleaned up if necessary.
> + * For the unlocked version of this call, also drop buffer_head reference.
>   *
>   * __jbd2_journal_refile_buffer is usually called as part of a single locked
     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Doesn't this paragraph refer to jbd2_journal_refile_buffer(), not
__jbd2_journal_refile_buffer()?  Or am I missing something?

>  void jbd2_journal_refile_buffer(journal_t *journal, struct journal_head *jh)
>  {
>  	struct buffer_head *bh = jh2bh(jh);
>  
> +	/* Get reference so that buffer cannot be freed before we unlock it */
> +	get_bh(bh);

OK, so we're adding a get_bh(bh) call to jbd2_journal_refile_buffer(),
which we're not freeing later in the function.  So this means every
single place where we call jbd2_journal_refile_buffer(), we'd better
add put_bh(bh) or bhrelse(bh) call, right?

So in fs/jbd2/commit.c, line 418, in jbd2_journal_commit_transaction(),
I see a call to jbd2_journal_refile_buffer(), which the patch doesn't
seem to adjust.  Looks like this could cause a buffer leak?

In your testing, have you checked to the slab cache to make sure there
isn't any memory leakage going on with buffer heads?

      	  	 	       	       - Ted
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