Re: [PATCH] printk: ringbuffer: fix error in comment

[Petr Mladek]

On Mon 2026-03-30 16:20:39, John Ogness wrote:
> On 2026-03-30, Petr Mladek <pmladek@xxxxxxxx> wrote:
> > On Mon 2026-03-30 10:12:08, John Ogness wrote:
> >> On 2026-03-27, Loïc Grégoire <loicgre@xxxxxxxxx> wrote:
> >> > The printk ringbuffer implementation is described in the comment as
> >> > using three ringbuffers, but the current implementation uses two (desc
> >> > and data). Update the comment so it matches the code.
> >> >
> >> > Signed-off-by: Loïc Grégoire <loicgre@xxxxxxxxx>
> >> 
> >> Reviewed-by: John Ogness <john.ogness@xxxxxxxxxxxxx>
> >
> > Reviewed-by: Petr Mladek <pmladek@xxxxxxxx>
> >
> >> However, this is only a single fixup when there are other documentation
> >> errors that need fixing as well. Does it make sense to commit such tiny
> >> fixups separately? For example, below are needed fixes that I am aware
> >> of.
> >> 
> >> Perhaps we should fold these into a single doc-fixup patch?
> >>
> >> diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c
> >> index 56c8e3d031f49..3f019207d2688 100644
> >> --- a/kernel/printk/printk_ringbuffer.c
> >> +++ b/kernel/printk/printk_ringbuffer.c
> >> @@ -224,7 +224,7 @@
> >>   *
> >>   *	prb_rec_init_rd(&r, &info, &text_buf[0], sizeof(text_buf));
> >>   *
> >> - *	prb_for_each_record(0, &test_rb, &seq, &r) {
> >> + *	prb_for_each_record(0, &test_rb, seq, &r) {
> >>   *		if (info.seq != seq)
> >>   *			pr_warn("lost %llu records\n", info.seq - seq);
> >>   *
> >> @@ -1365,7 +1365,7 @@ static struct prb_desc *desc_reopen_last(struct prb_desc_ring *desc_ring,
> >>  	 *
> >>  	 * WMB from _prb_commit:A to _prb_commit:B
> >>  	 *    matching
> >> -	 * MB If desc_reopen_last:A to prb_reserve_in_last:A
> >> +	 * MB from desc_reopen_last:A to prb_reserve_in_last:A
> >>  	 */
> >>  	if (!atomic_long_try_cmpxchg(&d->state_var, &prev_state_val,
> >>  			DESC_SV(id, desc_reserved))) { /* LMM(desc_reopen_last:A) */
> >> @@ -1770,9 +1770,9 @@ static void _prb_commit(struct prb_reserved_entry *e, unsigned long state_val)
> >>  	 *
> >>  	 *    Relies on:
> >>  	 *
> >> -	 *    MB _prb_commit:B to prb_commit:A
> >> +	 *    MB from _prb_commit:B to prb_commit:A
> >>  	 *       matching
> >> -	 *    MB desc_reserve:D to desc_make_final:A
> >> +	 *    MB from desc_reserve:D to desc_make_final:A
> >>  	 */
> >>  	if (!atomic_long_try_cmpxchg(&d->state_var, &prev_state_val,
> >>  			DESC_SV(e->id, state_val))) { /* LMM(_prb_commit:B) */
> >> @@ -2035,7 +2035,7 @@ u64 prb_first_seq(struct printk_ringbuffer *rb)
> >>  		 *
> >>  		 * MB from desc_push_tail:B to desc_reserve:F
> >>  		 *    matching
> >> -		 * RMB prb_first_seq:B to prb_first_seq:A
> >> +		 * RMB from prb_first_seq:B to prb_first_seq:A
> >>  		 */
> >>  		smp_rmb(); /* LMM(prb_first_seq:C) */
> >>  	}
> >> diff --git a/kernel/printk/printk_ringbuffer.h b/kernel/printk/printk_ringbuffer.h
> >> index 1651b53ece34f..fb7d2ee29af23 100644
> >> --- a/kernel/printk/printk_ringbuffer.h
> >> +++ b/kernel/printk/printk_ringbuffer.h
> >> @@ -388,7 +388,7 @@ for ((s) = from; prb_read_valid(rb, s, r); (s) = (r)->info->seq + 1)
> >>   *
> >>   * This is a macro for conveniently iterating over a ringbuffer.
> >>   * Note that @s may not be the sequence number of the record on each
> >> - * iteration. For the sequence number, @r->info->seq should be checked.
> >> + * iteration. For the sequence number, @i->seq should be checked.
> >>   *
> >>   * Context: Any context.
> >>   */
> >
> > All these changes look correct as well:
> >
> > Reviewed-by: Petr Mladek <pmladek@xxxxxxxx>
> >
> > I could squash these changes into the original patch when comitting
> > into printk/linux.git.
> >
> > John, could I use your Signed-off-by to mark you as a co-author
> > and keep Loïc as the author of the patch?
> 
> Signed-off-by: John Ogness <john.ogness@xxxxxxxxxxxxx>

JFYI, the patch has been comitted into printk/linux.git,
branch rework/prb-fixes.

I have merged the extra fixes proposed by John, see
https://git.kernel.org/pub/scm/linux/kernel/git/printk/linux.git/commit/?h=rework/prb-fixes&id=bf56987c111372a54ae877934a42f7fb0953a6ca

Best Regards,
Petr