[linux-lvm] Re: [OOPS] full snapshot (with test vfs locking patch for reiserfs snapshots in 11-pre)

[Chris Mason <mason@suse.com>]

On Monday, October 08, 2001 01:05:48 PM -0400 Ed Tomlinson <tomlins@CAM.ORG> wrote:

> On October 8, 2001 12:54 pm, Chris Mason wrote:
>> On Monday, October 08, 2001 11:53:46 AM -0400 Ed Tomlinson
>> 
>> <tomlins@CAM.ORG> wrote:
>> > Hi Chris,
>> > 
>> > To summerize, with 2.4.11-pre5 and lvm-1.01-rc4 + your test vfslocking
>> > patch  for 2.4.11-pre I, unlike you, was able to make snapshots and
>> > reiserfsck them without  problems.  Then I tried a debench 50 run and
>> > got an oops.
>> 
>> Confirmed, similar oops here.  Do you get this with rc4 in 2.4.10?
> 
> Funny you should ask...  Guess what was runing when this email arrived?
> The  answer is that with 2.4.10 + lvm 1.01-rc4 the snapshot deactivates
> correctly -  I do not see an oops.
>

Hmmm, looks like pure luck then.  It does not look like all the callers of lvm_snapshot_remap_block are properly checking to make sure the snapshot is still valid (hasn't been run through lvm_snapshot_release).

Try this:

-chris

Index: 0.21/drivers/md/lvm-snap.c
--- 0.21/drivers/md/lvm-snap.c Sat, 06 Oct 2001 00:07:22 -0400 
+++ 0.21(w)/drivers/md/lvm-snap.c Mon, 08 Oct 2001 13:35:41 -0400 
@@ -108,6 +108,9 @@
 	lv_block_exception_t * ret;
 	int i = 0;
 
+	if (!hash_table || !lv->lv_block_exception)
+		return NULL ;
+
 	hash_table = &hash_table[hashfn(org_dev, org_start, mask, chunk_size)];
 	ret = NULL;
 	for (next = hash_table->next; next != hash_table; next = next->next)
@@ -140,6 +143,8 @@
 	unsigned long mask = lv->lv_snapshot_hash_mask;
 	int chunk_size = lv->lv_chunk_size;
 
+	if (!hash_table)
+		BUG() ;
 	hash_table = &hash_table[hashfn(org_dev, org_start, mask, chunk_size)];
 	list_add(&exception->hash, hash_table);
 }