Re: [PATCH RESEND] block: warn if tag is greater than real_max_depth.

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Mon, Dec 19, 2011 at 5:11 PM, Tao Ma <tm@xxxxxx> wrote:
>>> Looks good, better than what we had. Applied.
>>
>> This appears to interact badly with scsi_adjust_queue_depth() when the
>> tag space shrinks.  I can reproduce a similar crash as reported in
>> "3.2-rc2+git: kernel BUG at block/blk-core.c:1000!
>> (__scsi_queue_insert)" [1].
>>
>> I can hit "kernel BUG at block/blk-core.c:2268!" which is the same
>> BUG_ON(blk_queued_rq(rq)) check reliably with:
>> # for i in $(seq 0 10); do dd if=/dev/zero of=/dev/sdX & done
>> # echo 4 > /sys/class/block/sdX/device/queue_depth
>>
>> The following fixes it for me, if this looks ok (versus reverting
>> commit 5e081591) I'll roll it into a formal patch with Ed and Meelis'
>> Reported-by.
> Interesting. If I read the code correctly, real_max_depth is the maximum
> queue depth we ever have and max_depth is the current depth.
>
> In your fix, we never resize the tag size to be smaller than max_depth.
> So I think this patch does expose some problem, but not lead to the BUG.

Yes, if we keep the "if (unlikely(tag >= bqt->max_depth))" check in
blk_queue_end_tag() then the side effect is that we can never shrink
the tag depth, which I don't think was intended.

> And in your new comment, you mentioned that "request between new_depth
> and max_depth can be in-flight", but max_depth <= real_max_depth, so
> what's wrong with the comment? Sorry, but am I missing something here?

Prior to the change blk_queue_end_tag() would continue to complete
requests with a tag > max_depth, now it silently drops them on the
floor leaving BUG_ON(blk_queued_rq(rq)) to trigger when we try to end
the request

> Having said that, I have tried the test in my machine here, but have no
> luck by now. My kernel version is 3.2.0-rc5+.

What controller are you using?  I am using the isci driver with a sas
disk.  Meelis saw it with aic7xxx on a parallel scsi disk.

--
Dan
--
To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html


[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Index of Archives]     [SCSI Target Devel]     [Linux SCSI Target Infrastructure]     [Kernel Newbies]     [IDE]     [Security]     [Git]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Linux ATA RAID]     [Linux IIO]     [Samba]     [Device Mapper]
  Powered by Linux