On Fri 2016-12-23 10:46:43, Sergey Senozhatsky wrote: > not every switch to printk_safe is "dictated" by logbuf_lock. > down_trylock_console_sem(), for instance, takes semaphore spin_lock > which already may be locked on the same CPU (*), so we need to be > in safe mode: > > vprintk_emit() > down_trylock() > raw_spin_lock_irqsave(&sem->lock, flags); > ... > raw_spin_unlock_irqrestore(&sem->lock, flags); > spin_dump() > printk() > vprintk_emit() > down_trylock() > raw_spin_lock_irqsave(&sem->lock, flags) << deadlock > > > and so on. IOW, "printk_save_enter()" != "logbuf_lock is acquired".
You are right. It seems that the printk_safe_enter_irq() printk_safe_exit_irq() printk_safe_enter_irqsave(flags) printk_safe_exit_irqrestore(flags) variants make sense and we will need them together with the logbuf_lock_*() stuff. > [..] > > PS: I still think if we could come with a better name than > > printk_safe() but I cannot find one. > > well, not that I'm the fan of printk_safe name, but can't think > of anything better. we make printk calls safe (deadlock safe) in > places where previously it was unsafe... quick-&-dirty name that > is implementation-specific -- printk_percpu_enter/exit, or > printk_pcpu_enter/exit... dunno. OK, let's stay with printk_safe :-) Best Reagards, Petr
