linux-kernel - [104/151] dm snapshot: cope with chunk size larger than origin

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Date:	Wed, 16 Dec 2009 19:56:41 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Mikulas Patocka <mpatocka@...hat.com>,
	Alasdair G Kergon <agk@...hat.com>
Subject: [104/151] dm snapshot: cope with chunk size larger than origin

2.6.32-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Mikulas Patocka <mpatocka@...hat.com>

commit 8e87b9b81b3c370f7e53c1ab6e1c3519ef37a644 upstream.

Under some special conditions the snapshot hash_size is calculated as zero.
This patch instead sets a minimum value of 64, the same as for the
pending exception table.

rounddown_pow_of_two(0) is an undefined operation (it expands to shift
by -1).  init_exception_table with an argument of 0 would fail with -ENOMEM.

The way to trigger the problem is to create a snapshot with a chunk size
that is larger than the origin device.

Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>
Signed-off-by: Alasdair G Kergon <agk@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

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

--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -553,6 +553,8 @@ static int init_hash_tables(struct dm_sn
 	hash_size = min(origin_dev_size, cow_dev_size) >> s->store->chunk_shift;
 	hash_size = min(hash_size, max_buckets);
 
+	if (hash_size < 64)
+		hash_size = 64;
 	hash_size = rounddown_pow_of_two(hash_size);
 	if (init_exception_table(&s->complete, hash_size,
 				 DM_CHUNK_CONSECUTIVE_BITS))


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