Messages in this thread | | | Subject | Re: [PATCH v2 2/2] tty: use tty_init_dev_retry() to workaround a race condition | From | Jiri Slaby <> | Date | Fri, 22 Nov 2019 10:05:09 +0100 |
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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. >>> 'tty->port' will be set by the driver and if the driver has not yet done >>> it before we open the tty device we can get to this situation. By adding >>> some extra debug prints, I noticed that: >>> >>> 6.650130: uart_add_one_port >>> 6.663849: register_console >>> 6.664846: tty_open >>> 6.674391: tty_init_dev >>> 6.675456: tty_port_link_device >>> >>> 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?
thanks, -- js suse labs
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