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SubjectRe: [BUG] 2.6.21-rc1,2,3 regressions on my system that I found so far
Date
On Friday 16 March 2007 06:30, Maxim Levitsky wrote:
>
> Good day,
>
> I want to report regressions I have with 2.6.21-rc3 kernel.
> I use CONFIG_NO_HZ.

Do any of these issues go away with CONFIG_NO_HZ=n (or boot with nohz=n)
or are they all independent of it?

thanks,
-Len

> 1) Both suspend to disk and suspend to RAM are completely broken:
> On vanilla 2.6.20 suspend to disk works perfectly and suspend to ram works _almost_ perfectly (I will tell about that later).
> On 2.6.21-rc1 and later system hangs even before suspend begins (suspend to disk hangs before image write , and after suspend to ram ,
> some devices are powered down (disk,power leds) , and some and not(fans, power) , and system hangs).
>
> I did a git-bisect and I found which commit caused that:
> e3c7db621bed4afb8e231cb005057f2feb5db557 - [PATCH] [PATCH] PM: Change code ordering in main.c (breaks S3)
> ed746e3b18f4df18afa3763155972c5835f284c5 - [PATCH] [PATCH] swsusp: Change code ordering in disk.c (breaks swsusp, I don't use it, but I tested it)
> 259130526c267550bc365d3015917d90667732f1 - [PATCH] [PATCH] swsusp: Change code ordering in user.c (breaks uswsusp, that I use)
>
> I reverted those commits and now system suspends correctly to disk, but suspend to ram showed some more regressions.
>
>
> 2) ) After suspend to ram I get this
>
> Mar 14 00:22:23 MAIN kernel: [ 2.072875] caller is check_tsc_sync_source+0x1d/0x100
> Mar 14 00:22:23 MAIN kernel: [ 2.072878] [show_trace_log_lvl+26/48] show_trace_log_lvl+0x1a/0x30
> Mar 14 00:22:23 MAIN kernel: [ 2.072881] [show_trace+18/32] show_trace+0x12/0x20
> Mar 14 00:22:23 MAIN kernel: [ 2.072884] [dump_stack+22/32] dump_stack+0x16/0x20
> Mar 14 00:22:23 MAIN kernel: [ 2.072887] [debug_smp_processor_id+173/176] debug_smp_processor_id+0xad/0xb0
> Mar 14 00:22:23 MAIN kernel: [ 2.072891] [check_tsc_sync_source+29/256] check_tsc_sync_source+0x1d/0x100
> Mar 14 00:22:23 MAIN kernel: [ 2.072894] [__cpu_up+80/384] __cpu_up+0x50/0x180
> Mar 14 00:22:23 MAIN kernel: [ 2.072897] [_cpu_up+98/208] _cpu_up+0x62/0xd0
> Mar 14 00:22:23 MAIN kernel: [ 2.072901] [cpu_up+46/80] cpu_up+0x2e/0x50
> Mar 14 00:22:23 MAIN kernel: [ 2.072903] [enable_nonboot_cpus+110/160] enable_nonboot_cpus+0x6e/0xa0
> Mar 14 00:22:23 MAIN kernel: [ 2.072906] [enter_state+326/496] enter_state+0x146/0x1f0
> Mar 14 00:22:23 MAIN kernel: [ 2.072909] [state_store+174/192] state_store+0xae/0xc0
> Mar 14 00:22:23 MAIN kernel: [ 2.072912] [subsys_attr_store+43/64] subsys_attr_store+0x2b/0x40
> Mar 14 00:22:23 MAIN kernel: [ 2.072917] [sysfs_write_file+186/272] sysfs_write_file+0xba/0x110
> Mar 14 00:22:23 MAIN kernel: [ 2.072920] [vfs_write+150/352] vfs_write+0x96/0x160
> Mar 14 00:22:23 MAIN kernel: [ 2.072923] [sys_write+61/112] sys_write+0x3d/0x70
> Mar 14 00:22:23 MAIN kernel: [ 2.072926] [sysenter_past_esp+93/153] sysenter_past_esp+0x5d/0x99
> Mar 14 00:22:23 MAIN kernel: [ 2.072929] =======================
> Mar 14 00:22:23 MAIN kernel: [ 2.072931] checking TSC synchronization [CPU#0 -> CPU#1]:
> Mar 14 00:22:23 MAIN kernel: [ 2.092922] Measured 72051818872 cycles TSC warp between CPUs, turning off
>
> It looks clear that preempt is enabled all the way in second cpu initialization, ( I think that at least in check_tsc_sync_source, it should be disabled,
> shouldn't it ? )
>
> Then I did add preempt_disable() / preempt_enable() to this function , and I still got this:
>
> Mar 14 00:22:23 MAIN kernel: [ 2.072931] checking TSC synchronization [CPU#0 -> CPU#1]:
> Mar 14 00:22:23 MAIN kernel: [ 2.092922] Measured 72051818872 cycles TSC warp between CPUs, turning off
>
> It happens after second CPU is brought back on-line.
>
> Now I understand that this is TSC sync problem and I tried to do some tests:
>
> I tried to disable/enable second CPU by hand, eg I did number of times,
>
> echo "0" > /sys/devices/system/cpu/cpu1/online
> echo "1" > /sys/devices/system/cpu/cpu1/online
>
> and TSC sync was ok.
>
> Then I disabled 2nd CPU, have suspended system to RAM , resumed it , and then enabled 2nd CPU and got same error message.
> Then I disabled cpufreq , and did above tests, and got same results.
> I think that maybe this error is false, that there is some difference in TSC clock, but this difference is constant, and can be fixed
>
> 3) Sometimes I get this (once in three boots or so)
>
> [ 36.217405] ENABLING IO-APIC IRQs
> [ 36.217587] ..TIMER: vector=0x31 apic1=0 pin1=2 apic2=-1 pin2=-1
> [ 36.433917] APIC timer disabled due to verification failure.
>
> And NO_HZ is disabled due to that (I get 1000/s timer's interrupts)
> I haven't investigated that yet.
> It looks like another new test that my hardware fails to perform...
>
>
> And now I want to tell you about that _almost_ working suspend to ram I got in 2.6.20:
> To put it simply sometimes system wakes from resume, and sometimes not (about 1 in 5 times)
> When it does it works perfectly.
>
> This is quite common problem but ironically my case is very different and harder to solve.
>
> The fact is that I found thanks to RTC tricks , similar to PM_TRACE that system hangs in exactly three places (in one of them of course)
>
> I put between instructions, code like that to save a position in RTC alarm which is not cleared on reboot
> Note that this code uses ax, but I checked every time I put it that ax can be used (eg, it is loaded in next instruction)
>
> #define TRACE(val) \
> movb $0x01, %al ; \
> outb %al, $0x70 ; \
> movb $ ## val, %al ; \
> outb %al, $0x71
>
> It hangs very early in asm code, and those are places:
>
> 1) /home/maxim/software/kernel/linux-2.6.20-mod/arch/i386/kernel/acpi/wakeup.S:wakeup_start:
> ljmpl $__KERNEL_CS,$wakeup_pmode_return
> As I see that is first time wakeup low page is addressing kernel memory by jumping to it.
>
> 2) /home/maxim/software/kernel/linux-2.6.20-mod/arch/i386/kernel/acpi/wakeup.S:do_suspend_lowlevel
> call restore_registers
> It hangs exacly on that instruction, I can only see that this is first time protected stack is accessed
>
> 3) /home/maxim/software/kernel/linux-2.6.20-mod/arch/i386/power/cpu.c :__restore_processor_state(struct saved_context *ctxt)
> mtrr_ap_init();
>
> It hangs somewhere inside this function, and because is is long I haven't found where exactly, it is easier to disable MTRR all together.
>
> Note that all three places have different external behavier:
>
> in first case, system powers on -> off -> on -> hangs
> I did put test in RTC to see whenever BIOS call kernel twice but I know from this test for sure that it calls it only once,
> It actualy makes sense, because exception occures before IDT is loaded, so system has no choice but to power down
>
> in second case I see blinking leds -> almost sure a oops
>
> in third case system just hangs
>
> That's all, I will continue to dig those problems out
>
> Thanks for attention,
> Maxim Levitsky
> -
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