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Commit 4407c2b6 authored by Jan Kara's avatar Jan Kara Committed by Linus Torvalds
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[PATCH] Fix race in do_get_write_access() 



  attached patch should fix the following race:
     Proc 1                               Proc 2

     __flush_batch()
       ll_rw_block()
                                        do_get_write_access()
					   lock_buffer
                                             jh is only waiting for checkpoint
					     -> b_transaction == NULL ->
					     do nothing
                                           unlock_buffer
    test_set_buffer_locked()
    test_clear_buffer_dirty()
                                           __journal_file_buffer()
                                        change the data
    submit_bh()

and we have sent wrong data to disk...  We now clean the dirty buffer flag
under buffer lock in all cases and hence we know that whenever a buffer is
starting to be journaled we either finish the pending write-out before
attaching a buffer to a transaction or we won't write the buffer until the
transaction is going to be committed.

The test in jbd_unexpected_dirty_buffer() is redundant - remove it.
Furthermore we have to clear the buffer dirty bit under the buffer lock to
prevent races with buffer write-out (and hence prevent returning a buffer with
IO happening).

Signed-off-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent e39f07c8

fs/jbd/transaction.c

+21 −18
Original line number Diff line number Diff line
@@ -490,10 +490,8 @@ void journal_unlock_updates (journal_t *journal) 
 */

static void jbd_unexpected_dirty_buffer(struct journal_head *jh)

{

	struct buffer_head *bh = jh2bh(jh);

	int jlist;



	if (buffer_dirty(bh)) {

	/* If this buffer is one which might reasonably be dirty

	 * --- ie. data, or not part of this journal --- then

	 * we're OK to leave it alone, but otherwise we need to
@@ -503,10 +501,10 @@ static void jbd_unexpected_dirty_buffer(struct journal_head *jh) 


	if (jlist == BJ_Metadata || jlist == BJ_Reserved ||

	    jlist == BJ_Shadow || jlist == BJ_Forget) {

			if (test_clear_buffer_dirty(jh2bh(jh))) {

				set_bit(BH_JBDDirty, &jh2bh(jh)->b_state);

			}

		}

		struct buffer_head *bh = jh2bh(jh);



		if (test_clear_buffer_dirty(bh))

			set_buffer_jbddirty(bh);

	}

}
@@ -574,10 +572,15 @@ do_get_write_access(handle_t *handle, struct journal_head *jh, 
			if (jh->b_next_transaction)

				J_ASSERT_JH(jh, jh->b_next_transaction ==

							transaction);

		}

		/*

		 * In any case we need to clean the dirty flag and we must

		 * do it under the buffer lock to be sure we don't race

		 * with running write-out.

		 */

		JBUFFER_TRACE(jh, "Unexpected dirty buffer");

		jbd_unexpected_dirty_buffer(jh);

 	}

 	}



	unlock_buffer(bh);