Messages in this thread | | | Date | Mon, 12 Oct 2009 13:55:49 +0200 | From | Ingo Molnar <> | Subject | Re: [crash] NULL pointer dereference at IP: [<ffffffff812e9ccb>] uart_close+0x2a/0x1e4 |
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* Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:
> > Unfortunately 46d57a449aa13d9c6adcc9d1dbc7b9a0ecfb69d8 is not easy to > > revert, at all. Would be glad to try any patch - fixes or some manual > > revert as well (if that's feasible). > > The patch doesn't do anything but create local variables of > state->port. I'm now glad I did it that way as it makes it easy to > spot the mistake. > > the tty_port lock is ->lock, the uart lock is ->lock both are > different.. > > Spot the mistake: > > if (state->flags & UIF_INITIALIZED) { > unsigned long flags; > spin_lock_irqsave(&port->lock, flags); > - port->ops->stop_rx(port); > + uport->ops->stop_rx(uport); > spin_unlock_irqrestore(&port->lock, flags); > /* > * Before we drop DTR, make sure the UART transmitter > * has completely drained; this is especially > * important if there is a transmit FIFO! > */ > - uart_wait_until_sent(tty, port->timeout); > + uart_wait_until_sent(tty, uport->timeout); > } > > > so uart_close takes the wrong lock. I've checked the rest of the patch > for the same error and I don't see any other screwups.
Cool! This very much looks like something that could fix both problems. I've started testing your fix.
And yeah, i too never ever regretted having done 'too finegrained' patches. (only ever the other way around) They are a pleasure to bisect back to.
> [...] The race in question is very hard to hit but fortunately Ingo > hit it twice..
a hundred thousand bootups a year go a long way in finding narrow races ;-)
Ingo
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