Messages in this thread | | | Date | Tue, 17 Dec 2019 13:05:15 +0100 | From | Greg Kroah-Hartman <> | Subject | Re: [PATCH v2 2/2] tty: use tty_init_dev_retry() to workaround a race condition |
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On Tue, Dec 17, 2019 at 11:47:25AM +0000, Sudip Mukherjee wrote: > Hi Greg, > > On Thu, Dec 12, 2019 at 11:15 AM Greg Kroah-Hartman > <gregkh@linuxfoundation.org> wrote: > > > > On Tue, Dec 10, 2019 at 11:41:47AM +0000, Sudip Mukherjee wrote: > > > Hi Jiri, > > > > > > On Fri, Nov 22, 2019 at 10:05:09AM +0100, Jiri Slaby wrote: > > > > On 21. 11. 19, 22:01, Sudip Mukherjee wrote: > > > > > Hi Greg, > > > > > > > > > > On Thu, Nov 21, 2019 at 05:41:38PM +0100, Greg Kroah-Hartman wrote: > > > > >> On Thu, Nov 21, 2019 at 03:22:39PM +0000, Sudip Mukherjee wrote: > > > > >>> There seems to be a race condition in tty drivers and I could see on > > > > >>> many boot cycles a NULL pointer dereference as tty_init_dev() tries to > > > > >>> do 'tty->port->itty = tty' even though tty->port is NULL. > > > <snip> > > > > >>> > > > > >>> uart_add_one_port() registers the console, as soon as it registers, the > > > > >>> userspace tries to use it and that leads to tty_open() but > > > > >>> uart_add_one_port() has not yet done tty_port_link_device() and so > > > > >>> tty->port is not yet configured when control reaches tty_init_dev(). > > > > >> > > > > >> Shouldn't we do tty_port_link_device() before uart_add_one_port() to > > > > >> remove that race? Once you register the console, yes, tty_open() can > > > > >> happen, so the driver had better be ready to go at that point in time. > > > > >> > > > > > > > > > > But tty_port_link_device() is done by uart_add_one_port() itself. > > > > > After registering the console uart_add_one_port() will call > > > > > tty_port_register_device_attr_serdev() and tty_port_link_device() is > > > > > called from this. Thats still tty core. > > > > > > > > Interferences of console vs tty code are ugly. Does it help to simply > > > > put tty_port_link_device to uart_add_one_port before uart_configure_port? > > > > > > sorry for the late response, got busy with an out-of-tree driver. > > > > > > It fixes the problem if I put tty_port_link_device() before > > > uart_configure_port(). Please check the attached patch and that > > > completely fixes the problem. Do you want me to send a proper patch for > > > it or do you want me to check more into it? > > > > This looks a lot more sane to me, can you resend it in proper format so > > that I can apply it? > > https://lore.kernel.org/lkml/20191212131602.29504-1-sudipm.mukherjee@gmail.com/
It's in my "to review" queue, don't worry, not lost :)
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