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dm snapshot: cope with chunk size larger than origin 

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.

Cc: stable@kernel.org
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
This commit is contained in:
Mikulas Patocka 2009-12-10 23:51:54 +00:00 committed by Alasdair G Kergon
parent 94e76572b5
commit 8e87b9b81b
1 changed files with 2 additions and 0 deletions
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2
drivers/md/dm-snap.c
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@ -553,6 +553,8 @@ static int init_hash_tables(struct dm_snapshot *s)
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))