Messages in this thread | | | Date | Wed, 8 Jun 2011 11:28:28 +0300 | From | Felipe Balbi <> | Subject | Re: tty breakage in X (Was: tty vs workqueue oddities) |
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Hi,
On Tue, Jun 07, 2011 at 07:44:48PM -0700, Linus Torvalds wrote: > On Mon, Jun 6, 2011 at 7:24 AM, Guillaume Chazarain <guichaz@gmail.com> wrote: > > > > After reverting http://git.kernel.org/linus/a5660b4 "tty: fix endless > > work loop when the buffer fills up" I cannot reproduce the hangs on > > SMP anymore but it brings back the busy loop on UP. > > Hmm. The n_tty layer has some rather distressing locking, and doesn't > lock "tty->receive_room" changes at all, for example (and uses > multiple locks for some other things). > > It may well be that there is some SMP race there. The n_tty line > discipline has its own locking for its counts, and the tty buffer code > has its own locking, and "receive_room" kind o fends up being in the > middle between them. > > The sad part is that the patch that made receive_buf() return the > amout of bytes received was actually trying to do the right thing, it > just did it entirely in the wrong way (re-introducing the crazy > re-arming of the workqueue from within itself, and using all the wrong > sign issues).
yeah sorry about that. I originally wrote that patch over one year ago and had to send it three times until it was finally noticed. Then I had to do a quick rebase and things went pretty bad.
Should've checked better and forget about loosing another merge window.
> I'd love to get rid of receive_room entirely - and just letting the > tty line discipline handler say how much it actually received. in > other words, having receive_buf() just tell us how much it used, and > not looking at receive_room in the caller is absolutely the right > thing.
that was the idea, unfortunately I missed the last part. Sorry about that.
-- balbi [unhandled content-type:application/pgp-signature] | |