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From: Greg KH on 12 Mar 2010 19:40
2.6.32-stable review patch. If anyone has any objections, please let me know.

----------------
From: Mikulas Patocka <mpatocka(a)redhat.com>

commit a97f925a32aad2a37971d7bfb657006acf04e42d upstream.

Free the dm_io structure before calling bio_endio() instead of after it,
to ensure that the io_pool containing it is not referenced after it is
freed.

This partially fixes a problem described here
https://www.redhat.com/archives/dm-devel/2010-February/msg00109.html

thread 1:
bio_endio(bio, io_error);
/* scheduling happens */
thread 2:
close the device
remove the device
thread 1:
free_io(md, io);

Thread 2, when removing the device, sees non-empty md->io_pool (because the
io hasn't been freed by thread 1 yet) and may crash with BUG in mempool_free.
Thread 1 may also crash, when freeing into a nonexisting mempool.

To fix this we must make sure that bio_endio() is the last call and
the md structure is not accessed afterwards.

There is another bio_endio in process_barrier, but it is called from the thread
and the thread is destroyed prior to freeing the mempools, so this call is
not affected by the bug.

A similar bug exists with module unloads - the module may be unloaded
immediately after bio_endio - but that is more difficult to fix.

Signed-off-by: Mikulas Patocka <mpatocka(a)redhat.com>
Signed-off-by: Alasdair G Kergon <agk(a)redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.de>

---
drivers/md/dm.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -614,8 +614,10 @@ static void dec_pending(struct dm_io *io
if (!md->barrier_error && io_error != -EOPNOTSUPP)
md->barrier_error = io_error;
end_io_acct(io);
+ free_io(md, io);
} else {
end_io_acct(io);
+ free_io(md, io);

if (io_error != DM_ENDIO_REQUEUE) {
trace_block_bio_complete(md->queue, bio);
@@ -623,8 +625,6 @@ static void dec_pending(struct dm_io *io
bio_endio(bio, io_error);
}
}
-
- free_io(md, io);
}
}



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