linux-kernel - Re: tty breakage in X (Was: tty vs workqueue oddities)

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Message-ID: <BANLkTikYjD2BnJz99xc-OEntAEJ0gUPztg@mail.gmail.com>
Date:	Tue, 7 Jun 2011 20:31:02 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Guillaume Chazarain <guichaz@...il.com>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, gregkh@...e.de,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Felipe Balbi <balbi@...com>, Tejun Heo <tj@...nel.org>
Subject: Re: tty breakage in X (Was: tty vs workqueue oddities)

On Tue, Jun 7, 2011 at 7:44 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> 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.

Actually, I think it's simpler than that.

Does this patch fix things for you? It just removes the "stop if
you've seen the tail, but somebody added a new buffer in the meantime"
logic.

We might want to keep the "re-arm the work" for just that case, but
let's see what happens if we just remove the logic entirely.

                          Linus

View attachment "patch.diff" of type "text/x-patch" (1494 bytes)