linux-kernel - Bug report: A commit about serial8250 cause the output disorderly at the phase of startup

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Date:   Fri, 19 Apr 2019 10:24:19 +0800
From:   "Hongzhi, Song" <hongzhi.song@...driver.com>
To:     <linux-kernel@...r.kernel.org>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        <john.ogness@...utronix.de>, <bigeasy@...utronix.de>
Subject: Bug report: A commit about serial8250 cause the output disorderly at
 the phase of startup

1. Issue description:

Boot kernel( >= linux-rt-devel-v5.0.3 ) with qemu.
Then qemu will print following disorderly messages.

At the beginning, the messages are disorderly. But then it becomes 
normally from printing "[    0.000000] 000: Linux version..."

--------------------------------------------------
[    0.019000] 000: tsc: Unable to calibrate against PIT
[    0.002583] 000: 6199.83 BogoMIPS (lpj=3099918)
[    0.521247] 000: Intel(R) Core(TM)2 Duo CPU     T7700  @ 2.40GHz
[    0.521247] 000:  (family: 0x6, model: 0xf
[    0.521247] 000: , stepping: 0xb)
[    0.533126] 000: unsupported p6 CPU model 15
[    0.533318] 000: no PMU driver, software events only.
[    0.765082] 000: 1 ACPI AML tables successfully acquired and loaded
[    0.765274] 000:
[    0.785903] 000: Enabled 2 GPEs in block 00 to 0F
[    0.786128] 000:
[    0.835675] 000: acpi PNP0A03:00: fail to add MMCONFIG information, 
can't access extended PCI configuration space under this bridge.
[    0.892056] 000:  5
[    0.892289] 000:  *10
[    0.892416] 000:  11
[    0.892527] 000: )
[    0.892661] 000:

/* skip some repeated contents */

[    5.052149] 000: , 512kB Cache
[    0.000000] 000: Linux version 5.0.3-yocto-preempt-rt+ 
(hsong@...-lpggp1) (gcc version 8.3.0 (GCC)) #24 SMP PREEMPT Thu Apr 18 
03:29:58 EDT 2019
[    0.000000] 000: Command line: root=/dev/vda rw highres=off 
console=ttyS0 mem=256M ip=192.168.7.4::192.168.7.3:255.255.255.0 vga=0 
uvesafb.mode_opti0
[    0.000000] 000: x86/fpu: x87 FPU will use FXSAVE
[    0.000000] 000: BIOS-provided physical RAM map:
[    0.000000] 000: BIOS-e820: [mem 0x0000000000000000-0x000000000009fbff]
[    0.000000] 000: BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff]
[    0.000000] 000: BIOS-e820: [mem 0x00000000000f0000-0x00000000000fffff]
[    0.000000] 000: BIOS-e820: [mem 0x0000000000100000-0x000000000ffdbfff]

--------------------------------------------------

2. Reproduce:
(1)build kernel: (Attachment is my .config)
make ARCH=x86_64 
CROSS_COMPILE=[path-to-my-cross-toolchain]/x86_64-wrs-linux-

(2)boot kernel with qemu:

qemu-system-x86_64 \
-drive file=qemux86-64.rootfs.ext4,if=virtio,format=raw \
-nographic \
-kernel arch/x86/boot/bzImage \
-append 'root=/dev/vda rw highres=off  console=ttyS0 mem=256M ip=dhcp'

3. Analysis:
I find the following commit from >=linux-rt-devel-v5.0.3. cause the issue.

b9d460e serial: 8250: implement write_atomic


View attachment "myconfig" of type "text/plain" (131630 bytes)