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/[email protected]/
>
> The 1st pa
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/[email protected]/
The 1st patch fixes the regression as agreed, see
https://lore.kernel
The decision whether some more space is needed is tricky in the printk
ring buffer code:
1. The given lpos values might overflow. A subtraction must be used
instead of a simple "lower than" check.
2. Another CPU might reuse the space in the mean time. It can be
detected when the sub
The commit 67e1b0052f6bb8 ("printk_ringbuffer: don't needlessly wrap
data blocks around") allows to use the last 4 bytes of the ring buffer.
But the check for the @data_size was not properly updated in get_data().
It fails when "blk_lpos->next" overflows to "0". In this case:
+ is_blk_wrapped(d
On Thu 2025-11-06 20:04:03, John Ogness wrote:
> On 2025-11-06, Petr Mladek wrote:
> >> diff --git a/kernel/printk/printk_ringbuffer.c
> >> b/kernel/printk/printk_ringbuffer.c
> >> index 839f504db6d30..8499ee642c31d 100644
> >> --- a/kernel/printk/printk_ringbuffer.c
> >> +++ b/kernel/printk/prin
On Thu 2025-11-06 12:42:21, John Ogness wrote:
> On 2025-11-05, John Ogness wrote:
> >> Another question is whether this is the only problem caused the patch.
> >
> > This comparison is quite special. It caught my attention while combing
> > through the code.
>
> The reason that this comparison i
On Wed 2025-11-05 16:00:28, John Ogness wrote:
> On 2025-11-04, Petr Mladek wrote:
> > Adding John into Cc.
>
> Thanks.
>
> > It rather looks like an internal bug in the printk_ringbuffer code.
> > And there is only one recent patch:
> >
> >https://patch.msgid.link/20250905144152.9137-2-d-ta
Adding John into Cc.
On Tue 2025-11-04 09:45:27, Joanne Koong wrote:
> On Mon, Nov 3, 2025 at 6:43 PM syzbot
> wrote:
> >
> > Hello,
> >
> > syzbot has tested the proposed patch but the reproducer is still triggering
> > an issue:
> > WARNING in get_data
> >
> > loop0: detected capacity change f
