On Thu, Feb 14, 2013 at 09:01:06PM +0100, Thomas Gleixner wrote: > commit 9ec1882df2 (tty: serial: imx: console write routing is unsafe > on SMP) introduced a recursive locking bug in imx_console_write(). > > The callchain is: > > imx_rxint() > spin_lock_irqsave(&sport->port.lock,flags); > ... > uart_handle_sysrq_char(); > sysrq_function(); > printk(); > imx_console_write(); > spin_lock_irqsave(&sport->port.lock,flags); <--- DEAD > > The bad news is that the kernel debugging facilities can dectect the > problem, but the printks never surface on the serial console for > obvious reasons. > > There is a similar issue with oops_in_progress. If the kernel crashes > we really don't want to be stuck on the lock and unable to tell what > happened. > > In general most UP originated drivers miss these checks and nobody > ever notices because CONFIG_PROVE_LOCKING seems to be still ignored by > a large number of developers. > > The solution is to avoid locking in the sysrq case and trylock in the > oops_in_progress case. > > This scheme is used in other drivers as well and it would be nice if > we could move this to a common place, so the usual copy/paste/modify > bugs can be avoided. I agree, making this easier to handle would be nice, patches are always accepted :) thanks, greg k-h -- 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
