Re: [PATCH printk v4 0/6] printk: remove safe buffers

From: Petr Mladek <pmladek@suse.com>
To: John Ogness <john.ogness@linutronix.de>
Cc: "Alexey Kardashevskiy" <aik@ozlabs.ru>,
	"Rasmus Villemoes" <linux@rasmusvillemoes.dk>,
	"Wolfram Sang (Renesas)" <wsa+renesas@sang-engineering.com>,
	"Paul Mackerras" <paulus@samba.org>,
	"Tiezhu Yang" <yangtiezhu@loongson.cn>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Marc Zyngier" <maz@kernel.org>,
	"Masahiro Yamada" <masahiroy@kernel.org>,
	"Russell King" <linux@armlinux.org.uk>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Yue Hu" <huyue2@yulong.com>, "Ingo Molnar" <mingo@redhat.com>,
	"Geert Uytterhoeven" <geert@linux-m68k.org>,
	linux-arm-kernel@lists.infradead.org,
	"Valentin Schneider" <valentin.schneider@arm.com>,
	"Kees Cook" <keescook@chromium.org>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	"Anshuman Khandual" <anshuman.khandual@arm.com>,
	"Vipin Sharma" <vipinsh@google.com>,
	"Frederic Weisbecker" <frederic@kernel.org>,
	"Nicholas Piggin" <npiggin@gmail.com>,
	"Nathan Chancellor" <nathan@kernel.org>,
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	"Steven Rostedt" <rostedt@goodmis.org>,
	"Thomas Gleixner" <tglx@linutronix.de>,
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	kexec@lists.infradead.org, linux-kernel@vger.kernel.org,
	"Sergey Senozhatsky" <senozhatsky@chromium.org>,
	"Eric Biederman" <ebiederm@xmission.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	linuxppc-dev@lists.ozlabs.org, "Mike Rapoport" <rppt@kernel.org>,
	"Cédric Le Goater" <clg@kaod.org>
Subject: Re: [PATCH printk v4 0/6] printk: remove safe buffers
Date: Tue, 27 Jul 2021 09:26:54 +0200	[thread overview]
Message-ID: <YP+1PqaKTfZXHjmU@alley> (raw)
In-Reply-To: <20210715193359.25946-1-john.ogness@linutronix.de>

On Thu 2021-07-15 21:39:53, John Ogness wrote:
> Hi,
> 
> Here is v4 of a series to remove the safe buffers. v3 can be
> found here [0]. The safe buffers are no longer needed because
> messages can be stored directly into the log buffer from any
> context.
> 
> However, the safe buffers also provided a form of recursion
> protection. For that reason, explicit recursion protection is
> implemented for this series.
> 
> The safe buffers also implicitly provided serialization
> between multiple CPUs executing in NMI context. This was
> particularly necessary for the nmi_backtrace() output. This
> serializiation is now preserved by using the printk cpulock.
> 
> With the removal of the safe buffers, there is no need for
> extra NMI enter/exit tracking. So this is also removed
> (which includes removing the config option CONFIG_PRINTK_NMI).
> 
> And finally, there are a few places in the kernel that need to
> specify code blocks where all printk calls are to be deferred
> printing. Previously the NMI tracking API was being (mis)used
> for this purpose. This series introduces an official and
> explicit interface for such cases. (Note that all deferred
> printing will be removed anyway, once printing kthreads are
> introduced.)
> 
> John Ogness (6):
>   lib/nmi_backtrace: explicitly serialize banner and regs
>   printk: track/limit recursion
>   printk: remove safe buffers
>   printk: remove NMI tracking
>   printk: convert @syslog_lock to mutex
>   printk: syslog: close window between wait and read

The entire patchset has been committed into printk/linux.git,
branch rework/printk_safe-removal.

Note that I have updated the 4th patch as discussed, see
https://lore.kernel.org/r/20210721120026.y3dqno24ahw4sazy@pathway.suse.cz
https://lore.kernel.org/r/20210721130852.zrjnti6b3fwjgdzj@pathway.suse.cz

Best Regards,
Petr