Re: [PATCHv5 05/17] tty: don't allow ldisc dcd_change() after ldischalt

[Alan Cox]

> Yes, indeed, it's a bug. Please consider the following example:
> 
>      CPU1                                      CPU2
> =========================================================
> uart_handle_dcd_change() {		tty_set_ldisc() {
>   ld = tty_ldisc_ref(...)			  ...

[We have a reference]
>   ...					  tty_ldisc_halt(...)
					  [Should block]

> I think tty code is exactly the right place to fix this bug; this is
> what my patch is for.

More special case magic on top of the current crap isn't the right fix
here, tty_ldisc_halt needs to wait for the references to hit zero.

Alan
 

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