[PATCH printk v5 6/6] printk: reimplement log_cont using record extension

[Marek Szyprowski]

Hi John,

On 14.09.2020 14:33, John Ogness wrote:
> Use the record extending feature of the ringbuffer to implement
> continuous messages. This preserves the existing continuous message
> behavior.
>
> Signed-off-by: John Ogness <john.ogness at linutronix.de>
> Reviewed-by: Petr Mladek <pmladek at suse.com>

This patch landed recently in linux-next as commit f5f022e53b87 
("printk: reimplement log_cont using record extension"). I've noticed 
that it causes a regression on my test system (ARM 32bit Samsung Exynos 
4412-based Trats2 board). The messages are printed correctly on the 
serial console during boot, but then when I run 'dmesg' command, the log 
is truncated.

Here is are the last lines of the dmesg log after this patch:

[    6.649018] Waiting 2 sec before mounting root device...
[    6.766423] dwc2 12480000.hsotg: new device is high-speed
[    6.845290] dwc2 12480000.hsotg: new device is high-speed
[    6.914217] dwc2 12480000.hsotg: new address 51
[    8.710351] RAMDISK: squashfs filesystem found at block 0

The corresponding dmesg lines before applying this patch:

[    8.864320] RAMDISK: squashfs filesystem found at block 0
[    8.868410] RAMDISK: Loading 37692KiB [1 disk] into ram disk... /
[    9.071670] /
[    9.262498] /
[    9.540711] /
[    9.818031] done.
[   10.660074] VFS: Mounted root (squashfs filesystem) readonly on 
device 1:0.
[   10.739525] EXT4-fs (mmcblk0p1): INFO: recovery required on readonly 
filesystem
[   10.745347] EXT4-fs (mmcblk0p1): write access will be enabled during 
recovery
[   10.861129] EXT4-fs (mmcblk0p1): recovery complete
[   10.878150] EXT4-fs (mmcblk0p1): mounted filesystem with ordered data 
mode. Opts: (null)
[   10.881811] VFS: Mounted root (ext4 filesystem) readonly on device 
179:49.
[   10.889858] Trying to move old root to /initrd ...
[   10.895192] okay
[   10.914411] devtmpfs: mounted
[   10.925087] Freeing unused kernel memory: 1024K
[   10.933222] Run /sbin/init as init process
[   10.941723]   with arguments:
[   10.949890]     /sbin/init
[   10.949900]   with environment:
[   10.949909]     HOME=/
[   10.949917]     TERM=linux
[   12.415991] random: systemd-udevd: uninitialized urandom read (16 
bytes read)
[   12.425361] random: systemd-udevd: uninitialized urandom read (16 
bytes read)
[   12.438578] random: systemd-udevd: uninitialized urandom read (16 
bytes read)

...

I can provide a complete logs if that helps.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland