On (03/13/19 09:19), John Ogness wrote: > >> Yes. I will post a series that only implements the ringbuffer using > >> your simplified API. That will be enough to remove printk_safe and > >> actually does most of the work of updating devkmsg, kmsg_dump, and > >> syslog. > > > > This may _not_ be enough to remove printk_safe. One of the reasons > > printk_safe "condom" came into existence was console_sem (which > > is a bit too important to ignore it): > > > > printk() > > console_trylock() > > console_unlock() > > up() > > raw_spin_lock_irqsave(&sem->lock, flags) > > __up() > > wake_up_process() > > WARN/etc > > printk() > > console_trylock() > > down_trylock() > > raw_spin_lock_irqsave(&sem->lock, flags) << deadlock > > > > Back then we were looking at > > > > printk->console_sem->lock->printk->console_sem->lock > > > > deadlock report from LG, if I'm not mistaken. > > The main drawback of printk_safe is the safe buffers, which, aside from > bogus timestamping, may never make it back to the printk log buffer. > > With the new ring buffer the safe buffers are not needed, even in the > recursive situation. As you are pointing out, the notification/wake > component of printk_safe will still be needed. I will leave that (small) > part in printk_safe.c. Yeah, all I'm saying is that as it stands new printk() is missing a huge and necessary part - console semaphore. And things can get very different once you add that missing part. It brings a lot of stuff back to printk. logbuf and logbuf_lock are not really huge printk problems. scheduler, timekeeping locks, etc. are much bigger ones. Those dependencies don't come from logbuf/logbuf_lock. -ss
