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Date: Fri, 23 Dec 2016 10:53:41 +0100 From: Petr Mladek <pmladek@...e.com> To: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com> Cc: Linus Torvalds <torvalds@...ux-foundation.org>, Andrew Morton <akpm@...ux-foundation.org>, Jan Kara <jack@...e.cz>, Tejun Heo <tj@...nel.org>, Calvin Owens <calvinowens@...com>, Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Andy Lutomirski <luto@...nel.org>, Peter Hurley <peter@...leysoftware.com>, linux-kernel@...r.kernel.org, Sergey Senozhatsky <sergey.senozhatsky@...il.com> Subject: Re: [PATCHv6 6/7] printk: use printk_safe buffers in printk 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
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