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
