Re: [PATCH] Always reset btree cursor after an insert

[Lachlan McIlroy <lachlan@sgi.com>]

Dave Chinner wrote:
> On Mon, Jun 16, 2008 at 12:21:33PM +1000, Lachlan McIlroy wrote:
>> After a btree insert operation a cursor can be invalid due to block
>> splits and a maybe a new root block.  We reset the cursor in
>> xfs_bmbt_insert() in the cases where we think we need to but it
>> isn't enough as we still see assertions.  Just do what we do elsewhere
>> and reset the cursor unconditionally.
> 
> Ok, so you should also kill the new code in the btree insert that
> revalidates the btree cursor. IIRC, this was the only place it was
> needed for....

That was the plan.

> 
>> --- fs/xfs/xfs_bmap.c_1.392	2008-06-03 12:20:14.000000000 +1000
>> +++ fs/xfs/xfs_bmap.c	2008-06-16 12:11:47.000000000 +1000
>> @@ -1745,11 +1745,17 @@ xfs_bmap_add_extent_unwritten_real(
>> 			if ((error = xfs_bmbt_insert(cur, &i)))
>> 				goto done;
>> 			ASSERT(i == 1);
>> -			if ((error = xfs_bmbt_increment(cur, 0, &i)))
>> +			/*
>> +			 * Reset the cursor, don't trust it after any insert
>> +			 * operation.
>> +			 */
> 
> /*
>  * reset the cursor to the position of the new extent we are about
>  * to insert as we can't trust it after the previous insert
>  */

Fair enough.

> 
>> +			if ((error = xfs_bmbt_lookup_eq(cur, new->br_startoff,
>> +					new->br_startblock, new->br_blockcount,
>> +					&i)))
>> 				goto done;
> 
> 
> 			error = xfs_bmbt_lookup_eq(cur, new->br_startoff,
> 					br_startblock, new->br_blockcount, &i);
> 			if (error)
> 				goto done;
> 
>> -			ASSERT(i == 1);
>> +			ASSERT(i == 0);
> 
> ASSERT? How about a WANT_CORRUPTED_GOTO()?

I was just being consistent with the rest of the code.  If you think this
ASSERT should be changed then what about all of them?

> 
>> 			/* new middle extent - newext */
>> -			cur->bc_rec.b = *new;
>> +			cur->bc_rec.b.br_state = new->br_state;
>> 			if ((error = xfs_bmbt_insert(cur, &i)))
>> 				goto done;
>> 			ASSERT(i == 1);
> 
> Cheers,
> 
> Dave.