Re: 2.4.20: Proccess stuck in __lock_page ...

[Andrea Arcangeli <andrea@suse.de>]

On Tue, May 27, 2003 at 01:50:55PM -0700, manish wrote:
> Andrea Arcangeli wrote:
> 
> >On Tue, May 27, 2003 at 01:42:32PM -0700, manish wrote:
> >
> >>Marc-Christian Petersen wrote:
> >>
> >>>On Tuesday 27 May 2003 22:20, Andrea Arcangeli wrote:
> >>>
> >>>Hi Andrea,
> >>>
> >>>
> >>>>>1. Stock 2.4.20
> >>>>>2. 2.4.20 with the io_request_lock removed.
> >>>>>The tests on the first one are still going. The tests on the second one
> >>>>>showed processes getting stuck for long times (> 5 minutes) and not
> >>>>>paused ...
> >>>>>
> >>>>sorry if it's a dumb question but what is the "io_request_lock removed"
> >>>>thing? Hope you didn't delete any io_request_lock, if you did you can
> >>>>get worse things than crashes (i.e. mm/fs corruption). the pausing bug
> >>>>was a genuine race (quite innocent, if you could trigger a disk unplug
> >>>>you could recover from it)
> >>>>
> >>>>Andrea
> >>>>
> >>>funny. I asked him the same ;)
> >>>
> >>>see his response:
> >>>
> >>>-----------------------------------------------------------------------
> >>>
> >>>>what is this io_request_lock patch you are talking about?
> >>>>
> >>>>ciao, Marc
> >>>>
> >>>We made some changes to the 2.4.20 kernel to remove the io_request_lock 
> >>>and replace with queue_lock and host_lock.
> >>>-----------------------------------------------------------------------
> >>>
> >>>ciao, Marc
> >>>
> >>We made a change in the 2.4.20 kernel to remove the io_request_lock and 
> >>replace with the host_lock and the queue_lock.  Probably, not a right 
> >>thing to do
> >>
> >
> >right you are, but never mind, only remeber e2fsck the fs before
> >booting the box so you don't risk fs corruption later with the solid
> >kernels.
> >
> >Andrea
> >
> So, does it imply that we cannot remove the io_request_lock in 2.4 at all?

io_request_lock can be at most made per-device in 2.4, this is just the
case in my tree for istance. Locks are there for a reason, unless you
redesign the code to work more scalar, you can't just drop them and
expect stuff to work. But the io_request_lock has nothing to do with
both the hangs and the delays, it only hurts scalability if you've lots
of devices and lots of cpus.

Andrea