Re: Bug report: A commit about serial8250 cause the output disorderly at the phase of startup

[Hongzhi, Song]

On 4/23/19 2:48 PM, John Ogness wrote:
> On 2019-04-22, Hongzhi, Song <hongzhi.song@xxxxxxxxxxxxx> wrote:
> > Anyone notice this issue?
> Yes, I am aware of the issue. It is actually a feature, not a bug. ;-)
> Individual LOG_CONT messages, when classified as emergency messages, are
> printed immediately to the console.

Yes, this is what I have acquired from commit log and code.

The emergency mechanism is a good way.


>   This makes them appear
> "disorderly". It is not yet clear how best to deal with LOG_CONT
> emergency messages.


Extracting a part of log from my LOG_CONT message,

[ÂÂÂ 0.761635] 000:Â (family: 0x6, model: 0xf
[ÂÂÂ 0.761635] 000: , stepping: 0xb)

It obviously separates a full line. Maybe it is not related to LOG_CONT. ^_^


The counterpart source code:

1499ÂÂÂÂ pr_cont(" (family: 0x%x, model: 0x%x", c->x86, c->x86_model);
1500
1501ÂÂÂÂ if (c->x86_stepping || c->cpuid_level >= 0)
1502ÂÂÂÂÂÂÂÂ pr_cont(", stepping: 0x%x)\n", c->x86_stepping);
1503ÂÂÂÂ else
1504ÂÂÂÂÂÂÂÂ pr_cont(")\n");


I don't know if the issue exists in other place except LOG_CONT.

But it indeed influences customer's judgement.


Thanks for you reply.

--Hongzhi


> But I suppose we should introduce a config option to
> disable atomic consoles altogether if users preferred buffered/delayed
> printk output.




> John Ogness
>
>
> > On 4/19/19 10:24 AM, Hongzhi, Song wrote:
> > > 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 "[ÂÂÂ 0.000000] 000: Linux version..."
> > >
> > > --------------------------------------------------
> > > [ÂÂÂ 0.019000] 000: tsc: Unable to calibrate against PIT
> > > [ÂÂÂ 0.002583] 000: 6199.83 BogoMIPS (lpj=3099918)
> > > [ÂÂÂ 0.521247] 000: Intel(R) Core(TM)2 Duo CPUÂÂÂÂ T7700Â @ 2.40GHz
> > > [ÂÂÂ 0.521247] 000:Â (family: 0x6, model: 0xf
> > > [ÂÂÂ 0.521247] 000: , stepping: 0xb)
> > > [ÂÂÂ 0.533126] 000: unsupported p6 CPU model 15
> > > [ÂÂÂ 0.533318] 000: no PMU driver, software events only.
> > > [ÂÂÂ 0.765082] 000: 1 ACPI AML tables successfully acquired and loaded
> > > [ÂÂÂ 0.765274] 000:
> > > [ÂÂÂ 0.785903] 000: Enabled 2 GPEs in block 00 to 0F
> > > [ÂÂÂ 0.786128] 000:
> > > [ÂÂÂ 0.835675] 000: acpi PNP0A03:00: fail to add MMCONFIG
> > > information, can't access extended PCI configuration space under
> > > this bridge.
> > > [ÂÂÂ 0.892056] 000:Â 5
> > > [ÂÂÂ 0.892289] 000:Â *10
> > > [ÂÂÂ 0.892416] 000:Â 11
> > > [ÂÂÂ 0.892527] 000: )
> > > [ÂÂÂ 0.892661] 000:
> > >
> > > /* skip some repeated contents */
> > >
> > > [ÂÂÂ 5.052149] 000: , 512kB Cache
> > > [ÂÂÂ 0.000000] 000: Linux version 5.0.3-yocto-preempt-rt+
> > > (hsong@pek-lpggp1) (gcc version 8.3.0 (GCC)) #24 SMP PREEMPT Thu Apr
> > > 18 03:29:58 EDT 2019
> > > [ÂÂÂ 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
> > > [ÂÂÂ 0.000000] 000: x86/fpu: x87 FPU will use FXSAVE
> > > [ÂÂÂ 0.000000] 000: BIOS-provided physical RAM map:
> > > [ÂÂÂ 0.000000] 000: BIOS-e820: [mem
> > > 0x0000000000000000-0x000000000009fbff]
> > > [ÂÂÂ 0.000000] 000: BIOS-e820: [mem
> > > 0x000000000009fc00-0x000000000009ffff]
> > > [ÂÂÂ 0.000000] 000: BIOS-e820: [mem
> > > 0x00000000000f0000-0x00000000000fffff]
> > > [ÂÂÂ 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