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SubjectRe: [2.6.23 PATCH 07/18] dm io: fix panic on large request
Chuck Ebbert wrote:

>> [ 126.754204] BUG: unable to handle kernel NULL pointer dereference at
>> virtual address 00000000

> mempool_free() was called with a NULL pool. That can't be good.
Yes, it is really not good :)

Attached patch fixes this problem, fix needed for stable tree too,
this is not regression, just very old bug...


From: Milan Broz <>

Flush workqueue before releasing bioset and mopools
in dm-crypt.
There can be finished but not yet released request.

Call chain causing oops:
run workqueue
<remove device request - remove mempool>
mempool_free(io, cc->io_pool);

This usually happens when cryptsetup create temporary
luks mapping in the beggining of crypt device activation.

When dm-core calls destructor crypt_dtr, no new request
are possible.

Signed-off-by: Milan Broz <>

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

Index: linux-2.6.22/drivers/md/dm-crypt.c
--- linux-2.6.22.orig/drivers/md/dm-crypt.c 2007-07-17 21:56:36.000000000 +0200
+++ linux-2.6.22/drivers/md/dm-crypt.c 2007-07-19 11:55:13.000000000 +0200
@@ -920,6 +920,8 @@ static void crypt_dtr(struct dm_target *
struct crypt_config *cc = (struct crypt_config *) ti->private;

+ flush_workqueue(_kcryptd_workqueue);

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