On 09/01/2014 08:08, Mark Roszko : > Just to sumarize the bug after poking before the patch: > systemd calls open/close on /dev/ttyS0 per line > atmel_shutdown executes on close > uart_timer_callback may fire during shutdown before timer is killed > tasklet gets scheduled after tasklet_kill > atmel_shutdown returns back to uart_close > dice roll: > if the tasklet executes before uart_close kills the tty references, > the kernel is fine <--- I saw this happening more often than > panics, around once every 3 resets > if the tasklet executes after uart_close kills the tty references, it panics > > I tested the patch by old fashion way of manual board resets with a > total of 70 resets each on two individual SAMA5D34-EK boards I have in > my possession programmed with the same patched kernel image and > rootfs. They did not panic once with the patch applied. Typically > before the patch the panic would occur around once every 10 resets if > not more often to the point it occured for 4 resets straight. > > I have been trying to automate the testing, even If I make sure > nothing is using ttyS0 and then run a program that spams open() > writev() and close() (systemd uses the syscalls) to print messages, it > will never panic so I'm possibly misunderstanding how the driver > startup/shutdown ops get triggered(which should just be open/close > respectively) or variable length of messages from systemd and timing > between messages contributes to being unlucky and having the timer > fire at the wrong time. > > But from manual testing I'm pretty confident the bug is fixed. Nice, thanks for the detailed feedback. So I send the patch for inclusion to Greg. Thanks for your help Mark. Best regards, -- Nicolas Ferre -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
