On (01/16/17 12:00), Petr Mladek wrote: [..] > > Makes perfect sense to me. The only thing that worries me is that it > > does change the logic slightly, and I'm not sure if this will have any > > ramifications with it. That is, console_unlock() use to always leave > > with console_may_schedule equal to zero, where console_unlock() clears > > it. With this change, console_unlock() no longer clears that variable. > > Will that have any side effects that we are unaware of? > > Good question! it does look a bit worrisome. > If I get it correctly, the variable should never be used without the > console semaphore. IMHO, if it was used without the semaphore or if > it was not set correctly when the semaphore was taken, it would be a > bug. It means that leaving the variable set might actually help > to find a buggy usage if there is any. > > My findings: > > + console_may_lock is set only by functions that get the console > semaphore. > > + The function that takes the semaphore and does not set the > variable is resume_console(). IMHO, it is a bug. > > We are on the safe side because the function is called from > the same context as suspend_console() and it allows rescheduling. > > > + I am not aware of any use of the variable without the > semaphore. But it is not easy to prove just be reading > the code. there is a function that clears @console_may_schedule out of console_sem scope - console_flush_on_panic(). so I *may be* can think about a worst case scenario of race condition between console_flush_on_panic()->console_may_schedule = 0 on panic CPU and console_unlock()->console_may_schedule = 1 from CPU that panic CPU failed to stop (smp_send_stop() can return with secondary CPUs still being online). thoughts? -ss -- To unsubscribe from this list: send the line "unsubscribe linux-fbdev" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
