Messages in this thread | | | Date | Thu, 21 Nov 2019 21:01:55 +0000 | From | Sudip Mukherjee <> | Subject | Re: [PATCH v2 2/2] tty: use tty_init_dev_retry() to workaround a race condition |
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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.
> This feels like it should be fixed by the caller, not in the tty core. > Any reason that can not happen?
tty_port_register_device_attr_serdev() is part of tty core. Or is my above understanding wrong?
-- Regards Sudip
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