Re: [PATCH 5/5] btrfs: add allocator_hint mode

[Goffredo Baroncelli <kreijack@libero.it>]

On 2/5/21 12:24 AM, Zygo Blaxell wrote:
> On Mon, Feb 01, 2021 at 10:28:20PM +0100, Goffredo Baroncelli wrote:
>> From: Goffredo Baroncelli <kreijack@inwind.it>
[...]
Hi Zygo
> 
> Well, I guess if you're going to keep putting the mount option in each
> new patch version, then I'm going to keep saying "please remove the
> mount option" from each new patch version.
> 
> The right side of this || can be deleted, and the entire patch 4/5
> (which adds the mount option).

In the next iteration I will move the "mount option" patch at the end of the chain; this will help you to remove this part of the patch that you don't like.

[...]



> 	(gdb) l *(btrfs_alloc_chunk+0x74b)
> 	0xffffffff8190c3ab is in btrfs_alloc_chunk (fs/btrfs/volumes.c:5047).
> 	5042            ndevs = 0;
> 	5043            while (ndevs < ctl->ndevs) {
> 	5044                    hint = devices_info[ndevs++].alloc_hint;

> 	5045                    while (devices_info[ndevs].alloc_hint == hint &&
> 	5046                           ndevs < ctl->ndevs)

this check is WRONG. The left and right side of && have to be swapped. Otherwise it is possible
an access to the last element+1 of the array before the out of bound check.
My fault.

> 	5047                                    ndevs++;
> 	5048                    if (ndevs >= ctl->devs_min)
> 	5049                            break;
> 	5050            }
> 	5051

BR
G.Baroncelli


> 
>> +		if (ndevs >= ctl->devs_min)
>> +			break;
>> +	}
>> +
>> +	BUG_ON(ndevs > ctl->ndevs);
>> +	ctl->ndevs = ndevs;
>> +
>>   	return 0;
>>   }
>>   
>> diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
>> index d776b7f55d56..31a3e4cf93b5 100644
>> --- a/fs/btrfs/volumes.h
>> +++ b/fs/btrfs/volumes.h
>> @@ -364,6 +364,7 @@ struct btrfs_device_info {
>>   	u64 dev_offset;
>>   	u64 max_avail;
>>   	u64 total_avail;
>> +	int alloc_hint;
>>   };
>>   
>>   struct btrfs_raid_attr {
>> -- 
>> 2.30.0
>>


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