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From: Petr Mladek <pmladek@suse.com>
To: John Ogness <john.ogness@linutronix.de>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel@vger.kernel.org,
	"Paul E. McKenney" <paulmck@kernel.org>
Subject: Re: [PATCH next v3 2/2] printk: fix cpu lock ordering
Date: Wed, 16 Jun 2021 13:30:34 +0200	[thread overview]
Message-ID: <YMng2vvhM1/ySW5X@alley> (raw)
In-Reply-To: <20210615174947.32057-3-john.ogness@linutronix.de>

On Tue 2021-06-15 19:55:47, John Ogness wrote:
> The cpu lock implementation uses a full memory barrier to take
> the lock, but no memory barriers when releasing the lock. This
> means that changes performed by a lock owner may not be seen by
> the next lock owner. This may have been "good enough" for use
> by dump_stack() as a serialization mechanism, but it is not
> enough to provide proper protection for a critical section.
> 
> Correct this problem by using acquire/release memory barriers
> for lock/unlock, respectively.
> 
> Note that it is not necessary for a cpu lock to disable
> interrupts. However, in upcoming work this cpu lock will be used
> for emergency tasks (for example, atomic consoles during kernel
> crashes) and any interruptions while holding the cpu lock should
> be avoided if possible.
> 
> Signed-off-by: John Ogness <john.ogness@linutronix.de>

The patch looks good to me, except for the problems already
reported for the 1st patch.

Best Regards,
Petr

      reply	other threads:[~2021-06-16 11:30 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-15 17:49 [PATCH next v3 0/2] introduce printk cpu lock John Ogness
2021-06-15 17:49 ` [PATCH next v3 1/2] dump_stack: move cpu lock to printk.c John Ogness
2021-06-15 21:33   ` John Ogness
2021-06-16  7:06     ` Sergey Senozhatsky
2021-06-16  7:29       ` John Ogness
2021-06-16 11:21         ` Petr Mladek
2021-06-16 13:40           ` John Ogness
2021-06-16 11:55         ` Sergey Senozhatsky
2021-06-15 17:49 ` [PATCH next v3 2/2] printk: fix cpu lock ordering John Ogness
2021-06-16 11:30   ` Petr Mladek [this message]

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