linux-kernel - Re: [PATCH 0/2] printk_ringbuffer: Fix regression in get

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Message-ID: <aRHZrgMXUeMMY_gf@pathway.suse.cz>
Date: Mon, 10 Nov 2025 13:25:18 +0100
From: Petr Mladek <pmladek@...e.com>
To: John Ogness <john.ogness@...utronix.de>
Cc: Joanne Koong <joannelkoong@...il.com>,
	"amurray @ thegoodpenguin . co . uk" <amurray@...goodpenguin.co.uk>,
	brauner@...nel.org, chao@...nel.org, djwong@...nel.org,
	jaegeuk@...nel.org, linux-f2fs-devel@...ts.sourceforge.net,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-xfs@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH 0/2] printk_ringbuffer: Fix regression in get_data() and
 clean up data size checks

On Fri 2025-11-07 20:47:18, Petr Mladek wrote:
> This is outcome of the long discussion about the regression caused
> by 67e1b0052f6bb82 ("printk_ringbuffer: don't needlessly wrap data blocks around"),
> see https://lore.kernel.org/all/69096836.a70a0220.88fb8.0006.GAE@google.com/
> 
> The 1st patch fixes the regression as agreed, see
> https://lore.kernel.org/all/87ecqb3qd0.fsf@jogness.linutronix.de/
> 
> The 2nd patch adds a helper function to unify the checks whether
> a more space is needed. I did my best to address all the concerns
> about various proposed variants.
> 
> Note that I called the new helper function "need_more_space()" in the end.
> It avoids all the problems with "before" vs. "lt" vs "le",
> and "_safe" vs. "_sane" vs. "_bounded".
> 
> IMHO, the name "need_more_space()" fits very well in all three
> locations, surprisingly even in data_realloc(). But it is possible
> that you disagree. Let me know if you hate it ;-)
> 
> 
> The patchset applies on top of printk/linux.git, branch for-6.19.
> It should apply on top of linux-next as well.
> 
> Petr Mladek (2):
>   printk_ringbuffer: Fix check of valid data size when blk_lpos
>     overflows
>   printk_ringbuffer: Create a helper function to decide whether a more
>     space is needed
> 
>  kernel/printk/printk_ringbuffer.c | 40 +++++++++++++++++++++++++------
>  1 file changed, 33 insertions(+), 7 deletions(-)

JFYI, the patchset has been comitted into printk/linux.git,
branch for-6.19.

Note that I have updated the Subject and a comment in the 2nd patch
as suggested by John, see
https://git.kernel.org/pub/scm/linux/kernel/git/printk/linux.git/commit/?h=for-6.19&id=394aa576c0b783ae728d87ed98fe4f1831dfd720

Best Regards,
Petr