Comment 178 for bug 620074

With the last patch, the problem is permanent on my notebook on a ext4 and ext3 partition. The io wait time is at 100% with heavy io. Mouse clicks are not recognised very often, or the keyboard input is delayed for up to 10 seconds (all under xorg).

I got a deadlock with the patch on kernel 2.6.28.2, but only once. The io wait time was at 100%, but there was no disc io any more. I could not start any programs or save some data, but I was able to use the running programs. I am not sure, if this is a problem caused by the patch or it is our problem. I got a complete freeze with clocksource=jiffies on a unpatched kernel with heavy io and heavy cpu usage too.

I have checked some timings in the block and elevator functions
(__make_request, get_request, get_request_wait, blk_complete_request, cfq_service_tree_add and cfq_add_rq_rb).
All the timings where below 5µs. At some points they are climbing to 80µs. But it looks good for me. In get_request_wait the writing dd processes are waiting up to one second for a new free request. It was only the dd processes or sometime the pdflush process. Should be OK.

Can prepare_to_wait_exclusive(&rl->wait[rw], &wait, TASK_UNINTERRUPTIBLE) in get_request_wait (blk-core.c) cause such a problem?