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Wed, 11 Dec 2024 07:03:42 -0800 (PST) Date: Wed, 11 Dec 2024 16:03:34 +0100 From: Petr Mladek To: John Ogness Cc: Sergey Senozhatsky , Steven Rostedt , linux-kernel@vger.kernel.org, Rik van Riel , Omar Sandoval Subject: Re: [PATCH printk v1 2/2] printk: Defer legacy printing when holding printk_cpu_sync Message-ID: References: <20241209111746.192559-1-john.ogness@linutronix.de> <20241209111746.192559-3-john.ogness@linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241209111746.192559-3-john.ogness@linutronix.de> On Mon 2024-12-09 12:23:46, John Ogness wrote: > The documentation of printk_cpu_sync_get() clearly states > that the owner must never perform any activities where it waits > for a CPU. For legacy printing there can be spinning on the > console_lock and on the port lock. Therefore legacy printing > must be deferred when holding the printk_cpu_sync. > > Note that in the case of emergency states, atomic consoles > are not prevented from printing when printk is deferred. This > is appropriate because they do not spin-wait indefinitely for > other CPUs. > It might be worth adding a reference to the original report to show that the problem is real. Reported-by: Rik van Riel Closes: https://lore.kernel.org/r/20240715232052.73eb7fb1@imladris.surriel.com > Signed-off-by: John Ogness > Fixes: 55d6af1d6688 ("lib/nmi_backtrace: explicitly serialize banner and regs") Anyway, it looks good. Reviewed-by: Petr Mladek Best Regards, Petr PS: I am going to wait few more days for eventual feedback. I'll push it when nobody complains. I could add the above mentioned references when pushing.