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

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Message-ID: <20251107194720.1231457-1-pmladek@suse.com>
Date: Fri,  7 Nov 2025 20:47:18 +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,
	Petr Mladek <pmladek@...e.com>
Subject: [PATCH 0/2] printk_ringbuffer: Fix regression in get_data() and clean up data size checks

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(-)

-- 
2.51.1