On Mon, Jul 10, 2017 at 2:59 PM, Petr Mladek <pmladek@xxxxxxxx> wrote: > On Sat 2017-07-08 22:30:47, Tetsuo Handa wrote: >> What I want to mention here is that messages which were sent to printk() >> were not printed to not only /dev/tty0 but also /dev/ttyS0 (I'm passing >> "console=ttyS0,115200n8 console=tty0" to kernel command line.) I don't care >> if output to /dev/tty0 is delayed, but I expect that output to /dev/ttyS0 >> is not delayed, for I'm anayzing things using printk() output sent to serial >> console (serial.log in my VMware configuration). Hitting this problem when we >> cannot allocate memory results in failing to save printk() output. Oops, it >> is sad. > > Would it be acceptable to remove "console=tty0" parameter and push > the messages only to the serial console? > > Also there is the patchset from Peter Zijlstra that allows to > use early console all the time, see > https://lkml.kernel.org/r/20161018170830.405990950@xxxxxxxxxxxxx > > > The current code flushes each line to all enabled consoles one > by one. If there is a deadlock in one console, everything > gets blocked. > > We are trying to make printk() more robust. But it is much more > complicated than we anticipated. Many changes open another can > of worms. It seems to be a job for years. > > >> Hmm... should we consider addressing console_sem problem before >> introducing printing kernel thread and offloading to that kernel thread? > > As Sergey said, the console rework seems to be much bigger task > than introducing the kthread. > > Also if we would want to handle each console separately (as a > fallback) it would be helpful to have separate kthread for each > enabled console or for the less reliable consoles at least. Since the console-loggin-in-kthread comes up routinely, and equally often people say "but I dont want to make my serial console delayed": Should we make kthread-based printk a per-console opt-in? fbcon and other horror shows with deep nesting of entire subsystems and their locking hierarchy would do that. Truly simple console drivers like serial or maybe logging to some firmware/platform service for recovery after rebooting would not. Of course we'd also need one kthread per console, and we'd need to have at least some per-console locking (plus an overall console lock on top for both registering/unregistering consoles and all the legacy users like fbdev that need much more work to untangle). We could even restrict the per-console locking (i.e. those which can go ahead while someone else is holding the main or other console_locks) just for those console drivers which do not use a kthread, to cut down the audit burden to something manageable. Just my 2 cents, thrown in from the sideline. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
