Re: [Qemu-devel] [PULL 3/6] iscsi: Fix divide-by-zero regression on raw SG devices

[Paolo Bonzini]

On 22/09/2016 19:34, Eric Blake wrote:
> On 09/22/2016 11:52 AM, Paolo Bonzini wrote:
>> From: Eric Blake <address@hidden>
>>
>> When qemu uses iscsi devices in sg mode, iscsilun->block_size
>> is left at 0.  Prior to commits cf081fca and similar, when
>> block limits were tracked in sectors, this did not matter:
>> various block limits were just left at 0.  But when we started
>> scaling by block size, this caused SIGFPE.
>>
> 
>> +++ b/block/iscsi.c
>> @@ -1813,19 +1813,23 @@ static void iscsi_refresh_limits(BlockDriverState 
>> *bs, Error **errp)
>>  
>>      IscsiLun *iscsilun = bs->opaque;
>>      uint64_t max_xfer_len = iscsilun->use_16_for_rw ? 0xffffffff : 0xffff;
>> +    unsigned int block_size = MIN_NON_ZERO(BDRV_SECTOR_SIZE,
>> +                                           iscsilun->block_size);
>>  
>> -    bs->bl.request_alignment = iscsilun->block_size;
>> +    assert(iscsilun->block_size >= BDRV_SECTOR_SIZE || bs->sg);
>> +
>> +    bs->bl.request_alignment = block_size;
> 
> Ouch. If iscsilun->block_size is 4k, this ends up changing
> bs->bl.request_alignment to 512, which is wrong. :(
> 
> If I'm in time, let's drop this from the pull request, and I'll send a
> followup patch.
> 

Fixed myself (s/MIN_NON_ZERO/MAX/) and v2 sent.

Paolo

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