@head_id points to the newest record, but the printing loop
exits when it increments to this value (before printing).

Exit the printing loop after the newest record has been printed.

The python-based function in scripts/gdb/linux/dmesg.py already
does this correctly.

Fixes: e60768311af8 ("scripts/gdb: update for lockless printk ringbuffer")
Cc: stable@vger.kernel.org
Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
 Documentation/admin-guide/kdump/gdbmacros.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kdump/gdbmacros.txt b/Documentation/admin-guide/kdump/gdbmacros.txt
index 82aecdcae8a6..030de95e3e6b 100644
--- a/Documentation/admin-guide/kdump/gdbmacros.txt
+++ b/Documentation/admin-guide/kdump/gdbmacros.txt
@@ -312,10 +312,10 @@ define dmesg
 			set var $prev_flags = $info->flags
 		end
 
-		set var $id = ($id + 1) & $id_mask
 		if ($id == $end_id)
 			loop_break
 		end
+		set var $id = ($id + 1) & $id_mask
 	end
 end
 document dmesg

base-commit: 1b929c02afd37871d5afb9d498426f83432e71c2
-- 
2.30.2

On Thu 2022-12-29 14:49:39, John Ogness wrote:
> @head_id points to the newest record, but the printing loop
> exits when it increments to this value (before printing).
> 
> Exit the printing loop after the newest record has been printed.
> 
> The python-based function in scripts/gdb/linux/dmesg.py already
> does this correctly.
> 
> Fixes: e60768311af8 ("scripts/gdb: update for lockless printk ringbuffer")
> Cc: stable@vger.kernel.org
> Signed-off-by: John Ogness <john.ogness@linutronix.de>

JFYI, the patch has been committed into printk/linux.git,
branch for-6.3.

Best Regards,
Petr

On Thu 2022-12-29 14:49:39, John Ogness wrote:
> @head_id points to the newest record, but the printing loop
> exits when it increments to this value (before printing).
> 
> Exit the printing loop after the newest record has been printed.
> 
> The python-based function in scripts/gdb/linux/dmesg.py already
> does this correctly.
> 
> Fixes: e60768311af8 ("scripts/gdb: update for lockless printk ringbuffer")
> Cc: stable@vger.kernel.org
> Signed-off-by: John Ogness <john.ogness@linutronix.de>

Great catch!

Reviewed-by: Petr Mladek <pmladek@suse.com>

Best Regards,
Petr