linux-kernel - Re: [Ext2-devel] [PATCH] fix ext3 mounts at 16T

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Date:	Fri, 18 Aug 2006 18:56:58 -0500
From:	Eric Sandeen <esandeen@...hat.com>
To:	Eric Sandeen <esandeen@...hat.com>, Mingming Cao <cmm@...ibm.com>,
	sho@...s.nec.co.jp, ext2-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: Re: [Ext2-devel] [PATCH] fix ext3 mounts at 16T

Andreas Dilger wrote:
> On Aug 18, 2006  12:39 -0500, Eric Sandeen wrote:
>> @@ -168,7 +168,7 @@ goal_in_my_reservation(struct ext3_reser
>>  	ext3_fsblk_t group_first_block, group_last_block;
>>  
>>  	group_first_block = ext3_group_first_block_no(sb, group);
>> -	group_last_block = group_first_block + EXT3_BLOCKS_PER_GROUP(sb) - 1;
>> +	group_last_block = group_first_block + (EXT3_BLOCKS_PER_GROUP(sb) - 1);
>>  
>>  	if ((rsv->_rsv_start > group_last_block) ||
>>  	    (rsv->_rsv_end < group_first_block))
>> @@ -897,7 +897,7 @@ static int alloc_new_reservation(struct 
>>  	spinlock_t *rsv_lock = &EXT3_SB(sb)->s_rsv_window_lock;
>>  
>>  	group_first_block = ext3_group_first_block_no(sb, group);
>> -	group_end_block = group_first_block + EXT3_BLOCKS_PER_GROUP(sb) - 1;
>> +	group_end_block = group_first_block + (EXT3_BLOCKS_PER_GROUP(sb) - 1);
>>  
>>  	if (grp_goal < 0)
>>  		start_block = group_first_block;
> 
> I don't see how these can make a difference?  Surely, if the intermediate
> sum overflows it will then underflow when "- 1" is done?  Not that I mind,
> per-se, just curious why you think this fixes anything.

Well, you're right, if it overflows then it will underflow again.  And I've not 
observed any actual failures, and I don't expect to.  But personally I guess I'd 
rather avoid the whole overflow in the first place... maybe I'm being silly.  :)

If you think it's unnecessary code churn then we can not make this change...

-Eric
-
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