From: John Ogness <john.ogness@linutronix.de>
To: "Petr Mladek" <pmladek@suse.com>,
"Thomas Weißschuh" <thomas.weissschuh@linutronix.de>,
"Dan Carpenter" <dan.carpenter@linaro.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
Sergey Senozhatsky <senozhatsky@chromium.org>,
Kees Cook <kees@kernel.org>,
"Gustavo A . R . Silva" <gustavoars@kernel.org>,
David Gow <davidgow@google.com>, Arnd Bergmann <arnd@kernel.org>,
Arnd Bergmann <arnd@arndb.de>,
linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org,
Petr Mladek <pmladek@suse.com>
Subject: Re: [PATCH 1/3] printk: ringbuffer: Explain why the KUnit test ignores failed writes
Date: Fri, 04 Jul 2025 13:34:23 +0206 [thread overview]
Message-ID: <844ivskxew.fsf@jogness.linutronix.de> (raw)
In-Reply-To: <20250702095157.110916-2-pmladek@suse.com>
On 2025-07-02, Petr Mladek <pmladek@suse.com> wrote:
> The KUnit test ignores prb_reserve() failures on purpose. It tries
> to push the ringbuffer beyond limits.
>
> Note that it is a know problem that writes might fail in this situation.
> printk() tries to prevent this problem by:
>
> + allocating big enough data buffer, see log_buf_add_cpu().
>
> + allocating enough descriptors by using small enough average
> record, see PRB_AVGBITS.
>
> + storing the record with disabled interrupts, see vprintk_store().
>
> Also the amount of printk() messages is always somehow bound in
> practice. And they are serialized when they are printed from
> many CPUs on purpose, for example, when printing backtraces.
>
> Signed-off-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
next prev parent reply other threads:[~2025-07-04 11:28 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-07-02 9:51 [PATCH 0/3] printk: KUnit: Followup fixes for the new KUnit test Petr Mladek
2025-07-02 9:51 ` [PATCH 1/3] printk: ringbuffer: Explain why the KUnit test ignores failed writes Petr Mladek
2025-07-04 11:28 ` John Ogness [this message]
2025-07-02 9:51 ` [PATCH 2/3] printk: kunit: support offstack cpumask Petr Mladek
2025-07-02 20:28 ` Nathan Chancellor
2025-07-08 14:24 ` Petr Mladek
2025-07-08 14:48 ` Arnd Bergmann
2025-07-09 11:36 ` Petr Mladek
2025-07-09 12:53 ` Thomas Weißschuh
2025-07-10 13:51 ` Petr Mladek
2025-07-10 14:08 ` Arnd Bergmann
2025-09-02 13:55 ` Petr Mladek
2025-07-03 14:36 ` kernel test robot
2025-07-02 9:51 ` [PATCH 3/3] printk: kunit: Fix __counted_by() in struct prbtest_rbdata Petr Mladek
2025-07-04 11:41 ` John Ogness
2025-07-02 15:48 ` [PATCH 0/3] printk: KUnit: Followup fixes for the new KUnit test Thomas Weißschuh
2025-07-10 15:29 ` Petr Mladek
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