On Mon, 2008-11-03 at 17:01 -0800, ron minnich wrote: > On Sun, Nov 2, 2008 at 9:55 PM, Roman Shaposhnik <[EMAIL PROTECTED]> wrote: > > when somebody tries to stop a process that is waiting for the IO the process > > doesn't get transferred to a Stopped state immediately but only when > > the scheduler sees it for the first time. This leads to a process writing to > > a /proc/n/ctl being put in a Stopwait state which is a bit inconvenient. > > > > Is there any way I can poke the target process so that it gets attention > > from the scheduler an can be put in a Stopped state? > > > > Hi Roman, what's the bigger picture here? I am trying to understand > ... sorry if I'm missing the obvious.
I'm glad you've asked ;-) In fact, there's a bigger context and it is around managing processes run by cpu(1) from the terminal host. I was planning on writing an email on that subject to this list over the weekend but I need to amass some level of intelligence in that area first. For now, though, the easiest way to illustrate my problem would be to imagine a situation where you want to write some data into a Data segment of the process that is waiting for the IO. Now, waiting for the IO is almost as good as state as Stopped (the process is stuck in kernel waiting to be put back on the runqueue) so one would expect the transition between these 2 states to be almost trivial. Literally, all I'm asking is -- "dear kernel, please don't advance this process even if you otherwise can". All I need is a frozen state so that I can manipulate some data. Yet, I can't figure out how to do that: term% ps | grep 310 glenda 310 0:00 0:00 24K Pread cat term% cat /proc/310/seg* Stack 0f000000 10000000 0 Text R 00001000 00006000 0 Data 00006000 00007000 0 Bss 00007000 00007000 0 term% dd -if /dev/zero -bs 1 -count 1 -of /proc/310/mem -seek 6100 write: bad process or channel control request 1+0 records in 0+0 records out Of course, the process is Spleeping, so we need to stop it: term% echo stop > /proc/310/ctl This hangs, so I'll provide some input to 'cat' so that it becomes Stopped and I can do: term% dd -if /dev/zero -bs 1 -count 1 -of /proc/310/mem -seek 6100 1+0 records in 1+0 records out But! I'm really stuck if I can't give that input to something that is Pread. How are debugging/analysis tools supposed to deal with a situation like that? I would imagine this to be a pretty common situation for them, right? Thanks, Roman.
