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[PATCH] Fix race in do_get_write_access()

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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: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Jan Kara 2005-09-06 15:19:17 -07:00 committed by Linus Torvalds
parent e39f07c83b
commit 4407c2b6b2
1 changed files with 20 additions and 17 deletions
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37
fs/jbd/transaction.c
View file

@ -490,23 +490,21 @@ 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
* move the dirty bit to the journal's own internal
* JBDDirty bit. */
jlist = jh->b_jlist;
/* 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
* move the dirty bit to the journal's own internal
* JBDDirty bit. */
jlist = jh->b_jlist;
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);
}
}
if (jlist == BJ_Metadata || jlist == BJ_Reserved ||
jlist == BJ_Shadow || jlist == BJ_Forget) {
struct buffer_head *bh = jh2bh(jh);
if (test_clear_buffer_dirty(bh))
set_buffer_jbddirty(bh);
}
}
@ -574,9 +572,14 @@ 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);
JBUFFER_TRACE(jh, "Unexpected dirty buffer");
jbd_unexpected_dirty_buffer(jh);
}
}
/*
* 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);