linux-kernel - Re: [RFC][PATCHv5 7/7] printk: remove zap

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Date:   Mon, 12 Dec 2016 17:37:27 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, Jan Kara <jack@...e.cz>,
        Tejun Heo <tj@...nel.org>, Calvin Owens <calvinowens@...com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [RFC][PATCHv5 7/7] printk: remove zap_locks() function

On Thu 2016-12-01 22:55:46, Sergey Senozhatsky wrote:
> We use printk-safe now which makes printk-recursion detection code
> in vprintk_emit() unreachable. The tricky thing here is that, apart
> from detecting and reporting printk recursions, that code also used
> to zap_locks() in case of panic() from the same CPU. However,
> zap_locks() does not look to be needed anymore:
> 
> 1) Since commit 08d78658f393 ("panic: release stale console lock to
>    always get the logbuf printed out") panic flushing of `logbuf' to
>    console ignores the state of `console_sem' by doing
>    	panic()
> 		console_trylock();
> 		console_unlock();
> 
> 2) Since commit cf9b1106c81c ("printk/nmi: flush NMI messages on the
>    system panic") panic attempts to zap the `logbuf_lock' spin_lock to
>    successfully flush nmi messages to `logbuf'.
> 
> Basically, it seems that we either already do what zap_locks() used to
> do but in other places or we ignore the state of the lock. The only
> reaming difference is that we don't re-init the console semaphore in
> printk_safe_flush_on_panic(), but this is not necessary because we
> don't call console drivers from printk_safe_flush_on_panic() due to
> the fact that we are using a deferred printk() version (as was
> suggested by Petr Mladek).
> 
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>

I like this patch. The code is unused after protecting the section
by printk_safe_enter()/exit(). And also the panic mode is handled
by the commits mentioned above.

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr