[Qemu-devel] Status of my hacks on the MTTCG WIP branch

[Qemu-devel] Status of my hacks on the MTTCG WIP branch

[Alex Bennée]

Hi Fred,

OK so I've made progress with the WIP branch you gave me to look at.
Basically I've:

 * re-based to recent master
 * fixed up exit_request/tcg_current_cpu (in tcg: switch on multithread)
 * dropped the TLS exit_request and tcg_current_cpu patch
 * dropped the WIP: lock patch (was breaking virtio due pushing up locks)

And I can boot upand run  a -smp 2-4 arm system without any major
issues. For reference see:

  https://github.com/stsquad/qemu/tree/mttcg/multi_tcg_v8_wip_ajb_fix_locks

What issues are you currently looking at with your work?

--
Alex Bennée

Re: [Qemu-devel] Status of my hacks on the MTTCG WIP branch

[Pranith Kumar]

[-- Attachment #1: Type: text/plain, Size: 2379 bytes --]

Hi Alex,

On Tue, Jan 12, 2016 at 12:29 PM, Alex Bennée <alex.bennee@linaro.org>
wrote:

>
https://github.com/stsquad/qemu/tree/mttcg/multi_tcg_v8_wip_ajb_fix_locks
>

I built this branch and ran an arm64 guest. It seems to be failing
similarly to what I reported earlier:

#0  0x00007ffff2211cc9 in __GI_raise (sig=sig@entry=6) at
../nptl/sysdeps/unix/sysv/linux/raise.c:56
#1  0x00007ffff22150d8 in __GI_abort () at abort.c:89
#2  0x000055555572014c in qemu_ram_addr_from_host_nofail
(ptr=0xffffffc000187863) at /home/pranith/devops/code/qemu/cputlb.c:357
#3  0x00005555557209dd in get_page_addr_code (env1=0x555556702058,
addr=18446743798833248356) at /home/pranith/devops/code/qemu/cputlb.c:568
#4  0x00005555556db98c in tb_find_physical (cpu=0x5555566f9dd0,
pc=18446743798833248356, cs_base=0, flags=18446744071830503424) at
/home/pranith/devops/code/qemu/cpu-exec.c:224
#5  0x00005555556dbaf4 in tb_find_slow (cpu=0x5555566f9dd0,
pc=18446743798833248356, cs_base=0, flags=18446744071830503424) at
/home/pranith/devops/code/qemu/cpu-exec.c:268
#6  0x00005555556dbc77 in tb_find_fast (cpu=0x5555566f9dd0) at
/home/pranith/devops/code/qemu/cpu-exec.c:311
#7  0x00005555556dc0f1 in cpu_arm_exec (cpu=0x5555566f9dd0) at
/home/pranith/devops/code/qemu/cpu-exec.c:492
#8  0x00005555557050ee in tcg_cpu_exec (cpu=0x5555566f9dd0) at
/home/pranith/devops/code/qemu/cpus.c:1486
#9  0x00005555557051af in tcg_exec_all (cpu=0x5555566f9dd0) at
/home/pranith/devops/code/qemu/cpus.c:1515
#10 0x0000555555704800 in qemu_tcg_cpu_thread_fn (arg=0x5555566f9dd0) at
/home/pranith/devops/code/qemu/cpus.c:1187
#11 0x00007ffff25a8182 in start_thread (arg=0x7fffd20c8700) at
pthread_create.c:312
#12 0x00007ffff22d547d in clone () at
../sysdeps/unix/sysv/linux/x86_64/clone.S:111

The arguments I used are as follows:

(gdb) show args

Argument list to give program being debugged when it is started is "-m
1024M -M virt -cpu cortex-a57 -global virtio-blk-device.scsi=off -device
virtio-scsi-device,id=scsi -drive
file=arm64disk.qcow2,id=coreimg,cache=unsafe,if=none -device
scsi-hd,drive=coreimg -netdev user,id=unet -device
virtio-net-device,netdev=unet -kernel vmlinuz -initrd initrd.img -append
root=/dev/sda2 -display sdl -redir tcp:2222::22 -smp 2".

Does something look obviously wrong to you in the arg list?

Thanks!
-- 
Pranith

[-- Attachment #2: Type: text/html, Size: 2687 bytes --]

Re: [Qemu-devel] Status of my hacks on the MTTCG WIP branch

[Alex Bennée]

Pranith Kumar <bobby.prani@gmail.com> writes:

> Hi Alex,
>
> On Tue, Jan 12, 2016 at 12:29 PM, Alex Bennée <alex.bennee@linaro.org>
> wrote:
>
>>
> https://github.com/stsquad/qemu/tree/mttcg/multi_tcg_v8_wip_ajb_fix_locks
>>
>
> I built this branch and ran an arm64 guest. It seems to be failing
> similarly to what I reported earlier:
>
> #0  0x00007ffff2211cc9 in __GI_raise (sig=sig@entry=6) at
> ../nptl/sysdeps/unix/sysv/linux/raise.c:56
> #1  0x00007ffff22150d8 in __GI_abort () at abort.c:89
> #2  0x000055555572014c in qemu_ram_addr_from_host_nofail
> (ptr=0xffffffc000187863) at /home/pranith/devops/code/qemu/cputlb.c:357
> #3  0x00005555557209dd in get_page_addr_code (env1=0x555556702058,
> addr=18446743798833248356) at /home/pranith/devops/code/qemu/cputlb.c:568
> #4  0x00005555556db98c in tb_find_physical (cpu=0x5555566f9dd0,
> pc=18446743798833248356, cs_base=0, flags=18446744071830503424) at
> /home/pranith/devops/code/qemu/cpu-exec.c:224
> #5  0x00005555556dbaf4 in tb_find_slow (cpu=0x5555566f9dd0,
> pc=18446743798833248356, cs_base=0, flags=18446744071830503424) at
> /home/pranith/devops/code/qemu/cpu-exec.c:268
> #6  0x00005555556dbc77 in tb_find_fast (cpu=0x5555566f9dd0) at
> /home/pranith/devops/code/qemu/cpu-exec.c:311
> #7  0x00005555556dc0f1 in cpu_arm_exec (cpu=0x5555566f9dd0) at
> /home/pranith/devops/code/qemu/cpu-exec.c:492
> #8  0x00005555557050ee in tcg_cpu_exec (cpu=0x5555566f9dd0) at
> /home/pranith/devops/code/qemu/cpus.c:1486
> #9  0x00005555557051af in tcg_exec_all (cpu=0x5555566f9dd0) at
> /home/pranith/devops/code/qemu/cpus.c:1515
> #10 0x0000555555704800 in qemu_tcg_cpu_thread_fn (arg=0x5555566f9dd0) at
> /home/pranith/devops/code/qemu/cpus.c:1187
> #11 0x00007ffff25a8182 in start_thread (arg=0x7fffd20c8700) at
> pthread_create.c:312
> #12 0x00007ffff22d547d in clone () at
> ../sysdeps/unix/sysv/linux/x86_64/clone.S:111
>
> The arguments I used are as follows:
>
> (gdb) show args
>
> Argument list to give program being debugged when it is started is "-m
> 1024M -M virt -cpu cortex-a57 -global virtio-blk-device.scsi=off -device
> virtio-scsi-device,id=scsi -drive
> file=arm64disk.qcow2,id=coreimg,cache=unsafe,if=none -device
> scsi-hd,drive=coreimg -netdev user,id=unet -device
> virtio-net-device,netdev=unet -kernel vmlinuz -initrd initrd.img -append
> root=/dev/sda2 -display sdl -redir tcp:2222::22 -smp 2".

With my command line:

/home/alex/lsrc/qemu/qemu.git/aarch64-softmmu/qemu-system-aarch64
-machine type=virt -display none -smp 1 -m 4096 -cpu cortex-a57 -serial
telnet:127.0.0.1:4444 -monitor stdio -netdev
user,id=unet,hostfwd=tcp::2222-:22 -device virtio-net-device,netdev=unet
-drive
file=/home/alex/lsrc/qemu/images/jessie-arm64.qcow2,id=myblock,index=0,if=none
-device virtio-blk-device,drive=myblock -kernel
/home/alex/lsrc/qemu/images/aarch64-current-linux-kernel-only.img
-append console=ttyAMA0 root=/dev/vda1 -s -name arm,debug-threads=on
-smp 4

I see the bad ram pointer failure in aarch64. It work in plain arm. Time
to dig out the debugging tools again ;-)

>
> Does something look obviously wrong to you in the arg list?
>
> Thanks!


--
Alex Bennée

Re: [Qemu-devel] Status of my hacks on the MTTCG WIP branch

[Alex Bennée]

Alex Bennée <alex.bennee@linaro.org> writes:

> Pranith Kumar <bobby.prani@gmail.com> writes:
>
>> Hi Alex,
>>
>> On Tue, Jan 12, 2016 at 12:29 PM, Alex Bennée <alex.bennee@linaro.org>
>> wrote:
>>
>>>
>> https://github.com/stsquad/qemu/tree/mttcg/multi_tcg_v8_wip_ajb_fix_locks
>>>
>>
>> I built this branch and ran an arm64 guest. It seems to be failing
>> similarly to what I reported earlier:
>>
>> #0  0x00007ffff2211cc9 in __GI_raise (sig=sig@entry=6) at
>> ../nptl/sysdeps/unix/sysv/linux/raise.c:56
>> #1  0x00007ffff22150d8 in __GI_abort () at abort.c:89
>> #2  0x000055555572014c in qemu_ram_addr_from_host_nofail
>> (ptr=0xffffffc000187863) at /home/pranith/devops/code/qemu/cputlb.c:357
>> #3  0x00005555557209dd in get_page_addr_code (env1=0x555556702058,
>> addr=18446743798833248356) at /home/pranith/devops/code/qemu/cputlb.c:568
>> #4  0x00005555556db98c in tb_find_physical (cpu=0x5555566f9dd0,
>> pc=18446743798833248356, cs_base=0, flags=18446744071830503424) at
>> /home/pranith/devops/code/qemu/cpu-exec.c:224
>> #5  0x00005555556dbaf4 in tb_find_slow (cpu=0x5555566f9dd0,
>> pc=18446743798833248356, cs_base=0, flags=18446744071830503424) at
>> /home/pranith/devops/code/qemu/cpu-exec.c:268
>> #6  0x00005555556dbc77 in tb_find_fast (cpu=0x5555566f9dd0) at
>> /home/pranith/devops/code/qemu/cpu-exec.c:311
>> #7  0x00005555556dc0f1 in cpu_arm_exec (cpu=0x5555566f9dd0) at
>> /home/pranith/devops/code/qemu/cpu-exec.c:492
>> #8  0x00005555557050ee in tcg_cpu_exec (cpu=0x5555566f9dd0) at
>> /home/pranith/devops/code/qemu/cpus.c:1486
>> #9  0x00005555557051af in tcg_exec_all (cpu=0x5555566f9dd0) at
>> /home/pranith/devops/code/qemu/cpus.c:1515
>> #10 0x0000555555704800 in qemu_tcg_cpu_thread_fn (arg=0x5555566f9dd0) at
>> /home/pranith/devops/code/qemu/cpus.c:1187
>> #11 0x00007ffff25a8182 in start_thread (arg=0x7fffd20c8700) at
>> pthread_create.c:312
>> #12 0x00007ffff22d547d in clone () at
>> ../sysdeps/unix/sysv/linux/x86_64/clone.S:111
<snip>

Having seen a backtrace of a crash while the other thread was flushing
the TLB entries I sprinkled a bunch of:

  g_assert(cpu == current_cpu);

In all public functions in cputlb that took a CPU. There are a bunch of
cases that don't defer actions across CPUs which need to be fixed up. I
suspect they don't hit in the arm case because the type of TLB flushing
pattern is different. In aarch64 it my backtrace it was triggered by
tlbi_aa64_vae1is_write:

  7    Thread 0x7ffe777fe700 (LWP 32705) "worker" sem_timedwait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/sem_timedwait.S:101
  6    Thread 0x7ffe77fff700 (LWP 32704) "worker" sem_timedwait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/sem_timedwait.S:101
  5    Thread 0x7fff8d9d0700 (LWP 32703) "CPU 1/TCG" 0x000055555572cc18 in memcpy (__len=8, __src=<synthetic pointer>, __dest=<optimised out>)
    at /usr/include/x86_64-linux-gnu/bits/string3.h:51
* 4    Thread 0x7fff8e1d1700 (LWP 32702) "CPU 0/TCG" memset () at ../sysdeps/x86_64/memset.S:94
  3    Thread 0x7fff8f1cb700 (LWP 32701) "worker" sem_timedwait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/sem_timedwait.S:101
  2    Thread 0x7fffe45c8700 (LWP 32700) "qemu-system-aar" syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
  1    Thread 0x7ffff7f98c00 (LWP 32696) "qemu-system-aar" 0x00007ffff0ba01ef in __GI_ppoll (fds=0x5555575cb5b0, nfds=8, timeout=<optimised out>,
    timeout@entry=0x7fffffffdf60, sigmask=sigmask@entry=0x0) at ../sysdeps/unix/sysv/linux/ppoll.c:56
#0  memset () at ../sysdeps/x86_64/memset.S:94
#1  0x0000555555728bee in memset (__len=32768, __ch=0, __dest=0x555556632568) at /usr/include/x86_64-linux-gnu/bits/string3.h:84
#2  v_tlb_flush_by_mmuidx (argp=0x7fff8e1d0430, cpu=0x555556632380) at /home/alex/lsrc/qemu/qemu.git/cputlb.c:136
#3  tlb_flush_page_by_mmuidx (cpu=cpu@entry=0x555556632380, addr=addr@entry=547976253440) at /home/alex/lsrc/qemu/qemu.git/cputlb.c:243
#4  0x00005555557fcb4a in tlbi_aa64_vae1is_write (env=<optimised out>, ri=<optimised out>, value=<optimised out>)
    at /home/alex/lsrc/qemu/qemu.git/target-arm/helper.c:2757
#5  0x00007fffa441dac5 in code_gen_buffer ()
#6  0x00005555556eef4b in cpu_tb_exec (tb_ptr=<optimised out>, cpu=0x5555565eddd0) at /home/alex/lsrc/qemu/qemu.git/cpu-exec.c:157
#7  cpu_arm_exec (cpu=cpu@entry=0x5555565eddd0) at /home/alex/lsrc/qemu/qemu.git/cpu-exec.c:520
#8  0x00005555557108e8 in tcg_cpu_exec (cpu=0x5555565eddd0) at /home/alex/lsrc/qemu/qemu.git/cpus.c:1486
#9  tcg_exec_all (cpu=0x5555565eddd0) at /home/alex/lsrc/qemu/qemu.git/cpus.c:1515
#10 qemu_tcg_cpu_thread_fn (arg=0x5555565eddd0) at /home/alex/lsrc/qemu/qemu.git/cpus.c:1187
#11 0x00007ffff0e80182 in start_thread (arg=0x7fff8e1d1700) at pthread_create.c:312
#12 0x00007ffff0bad47d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111
[Switching to thread 5 (Thread 0x7fff8d9d0700 (LWP 32703))]
#0  0x000055555572cc18 in memcpy (__len=8, __src=<synthetic pointer>, __dest=<optimised out>) at /usr/include/x86_64-linux-gnu/bits/string3.h:51
51	  return __builtin___memcpy_chk (__dest, __src, __len, __bos0 (__dest));
#0  0x000055555572cc18 in memcpy (__len=8, __src=<synthetic pointer>, __dest=<optimised out>) at /usr/include/x86_64-linux-gnu/bits/string3.h:51
#1  stq_he_p (v=<optimised out>, ptr=<optimised out>) at /home/alex/lsrc/qemu/qemu.git/include/qemu/bswap.h:292
#2  stq_le_p (v=547973099520, ptr=<optimised out>) at /home/alex/lsrc/qemu/qemu.git/include/qemu/bswap.h:327
#3  helper_le_stq_mmu (env=0x55555663a608, addr=18446743801961580216, val=547973099520, oi=<optimised out>, retaddr=140735948385557)
    at /home/alex/lsrc/qemu/qemu.git/softmmu_template.h:455
#4  0x00007fffa435ed17 in code_gen_buffer ()
#5  0x00005555556eef4b in cpu_tb_exec (tb_ptr=<optimised out>, cpu=0x555556632380) at /home/alex/lsrc/qemu/qemu.git/cpu-exec.c:157
#6  cpu_arm_exec (cpu=cpu@entry=0x555556632380) at /home/alex/lsrc/qemu/qemu.git/cpu-exec.c:520
#7  0x00005555557108e8 in tcg_cpu_exec (cpu=0x555556632380) at /home/alex/lsrc/qemu/qemu.git/cpus.c:1486
#8  tcg_exec_all (cpu=0x555556632380) at /home/alex/lsrc/qemu/qemu.git/cpus.c:1515
#9  qemu_tcg_cpu_thread_fn (arg=0x555556632380) at /home/alex/lsrc/qemu/qemu.git/cpus.c:1187
#10 0x00007ffff0e80182 in start_thread (arg=0x7fff8d9d0700) at pthread_create.c:312
#11 0x00007ffff0bad47d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111
A debugging session is active.

Needless to say anything messing with structures used by the other
threads needs to take great care or doom will occur ;-)

I'll look at fixing them up in my tree while Fred finishes his re-base.

--
Alex Bennée

Re: [Qemu-devel] Status of my hacks on the MTTCG WIP branch

[KONRAD Frederic]

Le 14/01/2016 14:10, Alex Bennée a écrit :
> Alex Bennée <alex.bennee@linaro.org> writes:
>
>> Pranith Kumar <bobby.prani@gmail.com> writes:
>>
>>> Hi Alex,
>>>
>>> On Tue, Jan 12, 2016 at 12:29 PM, Alex Bennée <alex.bennee@linaro.org>
>>> wrote:
>>>
>>> https://github.com/stsquad/qemu/tree/mttcg/multi_tcg_v8_wip_ajb_fix_locks
>>> I built this branch and ran an arm64 guest. It seems to be failing
>>> similarly to what I reported earlier:
>>>
>>> #0  0x00007ffff2211cc9 in __GI_raise (sig=sig@entry=6) at
>>> ../nptl/sysdeps/unix/sysv/linux/raise.c:56
>>> #1  0x00007ffff22150d8 in __GI_abort () at abort.c:89
>>> #2  0x000055555572014c in qemu_ram_addr_from_host_nofail
>>> (ptr=0xffffffc000187863) at /home/pranith/devops/code/qemu/cputlb.c:357
>>> #3  0x00005555557209dd in get_page_addr_code (env1=0x555556702058,
>>> addr=18446743798833248356) at /home/pranith/devops/code/qemu/cputlb.c:568
>>> #4  0x00005555556db98c in tb_find_physical (cpu=0x5555566f9dd0,
>>> pc=18446743798833248356, cs_base=0, flags=18446744071830503424) at
>>> /home/pranith/devops/code/qemu/cpu-exec.c:224
>>> #5  0x00005555556dbaf4 in tb_find_slow (cpu=0x5555566f9dd0,
>>> pc=18446743798833248356, cs_base=0, flags=18446744071830503424) at
>>> /home/pranith/devops/code/qemu/cpu-exec.c:268
>>> #6  0x00005555556dbc77 in tb_find_fast (cpu=0x5555566f9dd0) at
>>> /home/pranith/devops/code/qemu/cpu-exec.c:311
>>> #7  0x00005555556dc0f1 in cpu_arm_exec (cpu=0x5555566f9dd0) at
>>> /home/pranith/devops/code/qemu/cpu-exec.c:492
>>> #8  0x00005555557050ee in tcg_cpu_exec (cpu=0x5555566f9dd0) at
>>> /home/pranith/devops/code/qemu/cpus.c:1486
>>> #9  0x00005555557051af in tcg_exec_all (cpu=0x5555566f9dd0) at
>>> /home/pranith/devops/code/qemu/cpus.c:1515
>>> #10 0x0000555555704800 in qemu_tcg_cpu_thread_fn (arg=0x5555566f9dd0) at
>>> /home/pranith/devops/code/qemu/cpus.c:1187
>>> #11 0x00007ffff25a8182 in start_thread (arg=0x7fffd20c8700) at
>>> pthread_create.c:312
>>> #12 0x00007ffff22d547d in clone () at
>>> ../sysdeps/unix/sysv/linux/x86_64/clone.S:111
> <snip>
>
> Having seen a backtrace of a crash while the other thread was flushing
> the TLB entries I sprinkled a bunch of:
>
>    g_assert(cpu == current_cpu);
>
> In all public functions in cputlb that took a CPU. There are a bunch of
> cases that don't defer actions across CPUs which need to be fixed up. I
> suspect they don't hit in the arm case because the type of TLB flushing
> pattern is different. In aarch64 it my backtrace it was triggered by
> tlbi_aa64_vae1is_write:
>
>    7    Thread 0x7ffe777fe700 (LWP 32705) "worker" sem_timedwait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/sem_timedwait.S:101
>    6    Thread 0x7ffe77fff700 (LWP 32704) "worker" sem_timedwait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/sem_timedwait.S:101
>    5    Thread 0x7fff8d9d0700 (LWP 32703) "CPU 1/TCG" 0x000055555572cc18 in memcpy (__len=8, __src=<synthetic pointer>, __dest=<optimised out>)
>      at /usr/include/x86_64-linux-gnu/bits/string3.h:51
> * 4    Thread 0x7fff8e1d1700 (LWP 32702) "CPU 0/TCG" memset () at ../sysdeps/x86_64/memset.S:94
>    3    Thread 0x7fff8f1cb700 (LWP 32701) "worker" sem_timedwait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/sem_timedwait.S:101
>    2    Thread 0x7fffe45c8700 (LWP 32700) "qemu-system-aar" syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
>    1    Thread 0x7ffff7f98c00 (LWP 32696) "qemu-system-aar" 0x00007ffff0ba01ef in __GI_ppoll (fds=0x5555575cb5b0, nfds=8, timeout=<optimised out>,
>      timeout@entry=0x7fffffffdf60, sigmask=sigmask@entry=0x0) at ../sysdeps/unix/sysv/linux/ppoll.c:56
> #0  memset () at ../sysdeps/x86_64/memset.S:94
> #1  0x0000555555728bee in memset (__len=32768, __ch=0, __dest=0x555556632568) at /usr/include/x86_64-linux-gnu/bits/string3.h:84
> #2  v_tlb_flush_by_mmuidx (argp=0x7fff8e1d0430, cpu=0x555556632380) at /home/alex/lsrc/qemu/qemu.git/cputlb.c:136
> #3  tlb_flush_page_by_mmuidx (cpu=cpu@entry=0x555556632380, addr=addr@entry=547976253440) at /home/alex/lsrc/qemu/qemu.git/cputlb.c:243
> #4  0x00005555557fcb4a in tlbi_aa64_vae1is_write (env=<optimised out>, ri=<optimised out>, value=<optimised out>)
>      at /home/alex/lsrc/qemu/qemu.git/target-arm/helper.c:2757
> #5  0x00007fffa441dac5 in code_gen_buffer ()
> #6  0x00005555556eef4b in cpu_tb_exec (tb_ptr=<optimised out>, cpu=0x5555565eddd0) at /home/alex/lsrc/qemu/qemu.git/cpu-exec.c:157
> #7  cpu_arm_exec (cpu=cpu@entry=0x5555565eddd0) at /home/alex/lsrc/qemu/qemu.git/cpu-exec.c:520
> #8  0x00005555557108e8 in tcg_cpu_exec (cpu=0x5555565eddd0) at /home/alex/lsrc/qemu/qemu.git/cpus.c:1486
> #9  tcg_exec_all (cpu=0x5555565eddd0) at /home/alex/lsrc/qemu/qemu.git/cpus.c:1515
> #10 qemu_tcg_cpu_thread_fn (arg=0x5555565eddd0) at /home/alex/lsrc/qemu/qemu.git/cpus.c:1187
> #11 0x00007ffff0e80182 in start_thread (arg=0x7fff8e1d1700) at pthread_create.c:312
> #12 0x00007ffff0bad47d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111
> [Switching to thread 5 (Thread 0x7fff8d9d0700 (LWP 32703))]
> #0  0x000055555572cc18 in memcpy (__len=8, __src=<synthetic pointer>, __dest=<optimised out>) at /usr/include/x86_64-linux-gnu/bits/string3.h:51
> 51	  return __builtin___memcpy_chk (__dest, __src, __len, __bos0 (__dest));
> #0  0x000055555572cc18 in memcpy (__len=8, __src=<synthetic pointer>, __dest=<optimised out>) at /usr/include/x86_64-linux-gnu/bits/string3.h:51
> #1  stq_he_p (v=<optimised out>, ptr=<optimised out>) at /home/alex/lsrc/qemu/qemu.git/include/qemu/bswap.h:292
> #2  stq_le_p (v=547973099520, ptr=<optimised out>) at /home/alex/lsrc/qemu/qemu.git/include/qemu/bswap.h:327
> #3  helper_le_stq_mmu (env=0x55555663a608, addr=18446743801961580216, val=547973099520, oi=<optimised out>, retaddr=140735948385557)
>      at /home/alex/lsrc/qemu/qemu.git/softmmu_template.h:455
> #4  0x00007fffa435ed17 in code_gen_buffer ()
> #5  0x00005555556eef4b in cpu_tb_exec (tb_ptr=<optimised out>, cpu=0x555556632380) at /home/alex/lsrc/qemu/qemu.git/cpu-exec.c:157
> #6  cpu_arm_exec (cpu=cpu@entry=0x555556632380) at /home/alex/lsrc/qemu/qemu.git/cpu-exec.c:520
> #7  0x00005555557108e8 in tcg_cpu_exec (cpu=0x555556632380) at /home/alex/lsrc/qemu/qemu.git/cpus.c:1486
> #8  tcg_exec_all (cpu=0x555556632380) at /home/alex/lsrc/qemu/qemu.git/cpus.c:1515
> #9  qemu_tcg_cpu_thread_fn (arg=0x555556632380) at /home/alex/lsrc/qemu/qemu.git/cpus.c:1187
> #10 0x00007ffff0e80182 in start_thread (arg=0x7fff8d9d0700) at pthread_create.c:312
> #11 0x00007ffff0bad47d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111
> A debugging session is active.
>
> Needless to say anything messing with structures used by the other
> threads needs to take great care or doom will occur ;-)
>
> I'll look at fixing them up in my tree while Fred finishes his re-base.
>
> --
> Alex Bennée
Hi,

Is that possible those one have been added since the V7 version?
I saw some changes there.

Thanks,
Fred

Re: [Qemu-devel] Status of my hacks on the MTTCG WIP branch

[Alex Bennée]

KONRAD Frederic <fred.konrad@greensocs.com> writes:

> Le 14/01/2016 14:10, Alex Bennée a écrit :
>> Alex Bennée <alex.bennee@linaro.org> writes:
>>
>>> Pranith Kumar <bobby.prani@gmail.com> writes:
>>>
>>>> Hi Alex,
>>>>
>>>> On Tue, Jan 12, 2016 at 12:29 PM, Alex Bennée <alex.bennee@linaro.org>
>>>> wrote:
>>>>
>>>> https://github.com/stsquad/qemu/tree/mttcg/multi_tcg_v8_wip_ajb_fix_locks
>>>> I built this branch and ran an arm64 guest. It seems to be failing
>>>> similarly to what I reported earlier:
>>>>
>>>> #0  0x00007ffff2211cc9 in __GI_raise (sig=sig@entry=6) at
>>>> ../nptl/sysdeps/unix/sysv/linux/raise.c:56
>>>> #1  0x00007ffff22150d8 in __GI_abort () at abort.c:89
>>>> #2  0x000055555572014c in qemu_ram_addr_from_host_nofail
>>>> (ptr=0xffffffc000187863) at /home/pranith/devops/code/qemu/cputlb.c:357
>>>> #3  0x00005555557209dd in get_page_addr_code (env1=0x555556702058,
>>>> addr=18446743798833248356) at /home/pranith/devops/code/qemu/cputlb.c:568
>>>> #4  0x00005555556db98c in tb_find_physical (cpu=0x5555566f9dd0,
>>>> pc=18446743798833248356, cs_base=0, flags=18446744071830503424) at
>>>> /home/pranith/devops/code/qemu/cpu-exec.c:224
>>>> #5  0x00005555556dbaf4 in tb_find_slow (cpu=0x5555566f9dd0,
>>>> pc=18446743798833248356, cs_base=0, flags=18446744071830503424) at
>>>> /home/pranith/devops/code/qemu/cpu-exec.c:268
>>>> #6  0x00005555556dbc77 in tb_find_fast (cpu=0x5555566f9dd0) at
>>>> /home/pranith/devops/code/qemu/cpu-exec.c:311
>>>> #7  0x00005555556dc0f1 in cpu_arm_exec (cpu=0x5555566f9dd0) at
>>>> /home/pranith/devops/code/qemu/cpu-exec.c:492
>>>> #8  0x00005555557050ee in tcg_cpu_exec (cpu=0x5555566f9dd0) at
>>>> /home/pranith/devops/code/qemu/cpus.c:1486
>>>> #9  0x00005555557051af in tcg_exec_all (cpu=0x5555566f9dd0) at
>>>> /home/pranith/devops/code/qemu/cpus.c:1515
>>>> #10 0x0000555555704800 in qemu_tcg_cpu_thread_fn (arg=0x5555566f9dd0) at
>>>> /home/pranith/devops/code/qemu/cpus.c:1187
>>>> #11 0x00007ffff25a8182 in start_thread (arg=0x7fffd20c8700) at
>>>> pthread_create.c:312
>>>> #12 0x00007ffff22d547d in clone () at
>>>> ../sysdeps/unix/sysv/linux/x86_64/clone.S:111
>> <snip>
>>
>> Having seen a backtrace of a crash while the other thread was flushing
>> the TLB entries I sprinkled a bunch of:
>>
>>    g_assert(cpu == current_cpu);
>>
>> In all public functions in cputlb that took a CPU. There are a bunch of
>> cases that don't defer actions across CPUs which need to be fixed up. I
>> suspect they don't hit in the arm case because the type of TLB flushing
>> pattern is different. In aarch64 it my backtrace it was triggered by
>> tlbi_aa64_vae1is_write:
>>
>>    7    Thread 0x7ffe777fe700 (LWP 32705) "worker" sem_timedwait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/sem_timedwait.S:101
>>    6    Thread 0x7ffe77fff700 (LWP 32704) "worker" sem_timedwait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/sem_timedwait.S:101
>>    5    Thread 0x7fff8d9d0700 (LWP 32703) "CPU 1/TCG" 0x000055555572cc18 in memcpy (__len=8, __src=<synthetic pointer>, __dest=<optimised out>)
>>      at /usr/include/x86_64-linux-gnu/bits/string3.h:51
>> * 4    Thread 0x7fff8e1d1700 (LWP 32702) "CPU 0/TCG" memset () at ../sysdeps/x86_64/memset.S:94
>>    3    Thread 0x7fff8f1cb700 (LWP 32701) "worker" sem_timedwait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/sem_timedwait.S:101
>>    2    Thread 0x7fffe45c8700 (LWP 32700) "qemu-system-aar" syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
>>    1    Thread 0x7ffff7f98c00 (LWP 32696) "qemu-system-aar" 0x00007ffff0ba01ef in __GI_ppoll (fds=0x5555575cb5b0, nfds=8, timeout=<optimised out>,
>>      timeout@entry=0x7fffffffdf60, sigmask=sigmask@entry=0x0) at ../sysdeps/unix/sysv/linux/ppoll.c:56
>> #0  memset () at ../sysdeps/x86_64/memset.S:94
>> #1  0x0000555555728bee in memset (__len=32768, __ch=0, __dest=0x555556632568) at /usr/include/x86_64-linux-gnu/bits/string3.h:84
>> #2  v_tlb_flush_by_mmuidx (argp=0x7fff8e1d0430, cpu=0x555556632380) at /home/alex/lsrc/qemu/qemu.git/cputlb.c:136
>> #3  tlb_flush_page_by_mmuidx (cpu=cpu@entry=0x555556632380, addr=addr@entry=547976253440) at /home/alex/lsrc/qemu/qemu.git/cputlb.c:243
>> #4  0x00005555557fcb4a in tlbi_aa64_vae1is_write (env=<optimised out>, ri=<optimised out>, value=<optimised out>)
>>      at /home/alex/lsrc/qemu/qemu.git/target-arm/helper.c:2757
>> #5  0x00007fffa441dac5 in code_gen_buffer ()
>> #6  0x00005555556eef4b in cpu_tb_exec (tb_ptr=<optimised out>, cpu=0x5555565eddd0) at /home/alex/lsrc/qemu/qemu.git/cpu-exec.c:157
>> #7  cpu_arm_exec (cpu=cpu@entry=0x5555565eddd0) at /home/alex/lsrc/qemu/qemu.git/cpu-exec.c:520
>> #8  0x00005555557108e8 in tcg_cpu_exec (cpu=0x5555565eddd0) at /home/alex/lsrc/qemu/qemu.git/cpus.c:1486
>> #9  tcg_exec_all (cpu=0x5555565eddd0) at /home/alex/lsrc/qemu/qemu.git/cpus.c:1515
>> #10 qemu_tcg_cpu_thread_fn (arg=0x5555565eddd0) at /home/alex/lsrc/qemu/qemu.git/cpus.c:1187
>> #11 0x00007ffff0e80182 in start_thread (arg=0x7fff8e1d1700) at pthread_create.c:312
>> #12 0x00007ffff0bad47d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111
>> [Switching to thread 5 (Thread 0x7fff8d9d0700 (LWP 32703))]
>> #0  0x000055555572cc18 in memcpy (__len=8, __src=<synthetic pointer>, __dest=<optimised out>) at /usr/include/x86_64-linux-gnu/bits/string3.h:51
>> 51	  return __builtin___memcpy_chk (__dest, __src, __len, __bos0 (__dest));
>> #0  0x000055555572cc18 in memcpy (__len=8, __src=<synthetic pointer>, __dest=<optimised out>) at /usr/include/x86_64-linux-gnu/bits/string3.h:51
>> #1  stq_he_p (v=<optimised out>, ptr=<optimised out>) at /home/alex/lsrc/qemu/qemu.git/include/qemu/bswap.h:292
>> #2  stq_le_p (v=547973099520, ptr=<optimised out>) at /home/alex/lsrc/qemu/qemu.git/include/qemu/bswap.h:327
>> #3  helper_le_stq_mmu (env=0x55555663a608, addr=18446743801961580216, val=547973099520, oi=<optimised out>, retaddr=140735948385557)
>>      at /home/alex/lsrc/qemu/qemu.git/softmmu_template.h:455
>> #4  0x00007fffa435ed17 in code_gen_buffer ()
>> #5  0x00005555556eef4b in cpu_tb_exec (tb_ptr=<optimised out>, cpu=0x555556632380) at /home/alex/lsrc/qemu/qemu.git/cpu-exec.c:157
>> #6  cpu_arm_exec (cpu=cpu@entry=0x555556632380) at /home/alex/lsrc/qemu/qemu.git/cpu-exec.c:520
>> #7  0x00005555557108e8 in tcg_cpu_exec (cpu=0x555556632380) at /home/alex/lsrc/qemu/qemu.git/cpus.c:1486
>> #8  tcg_exec_all (cpu=0x555556632380) at /home/alex/lsrc/qemu/qemu.git/cpus.c:1515
>> #9  qemu_tcg_cpu_thread_fn (arg=0x555556632380) at /home/alex/lsrc/qemu/qemu.git/cpus.c:1187
>> #10 0x00007ffff0e80182 in start_thread (arg=0x7fff8d9d0700) at pthread_create.c:312
>> #11 0x00007ffff0bad47d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111
>> A debugging session is active.
>>
>> Needless to say anything messing with structures used by the other
>> threads needs to take great care or doom will occur ;-)
>>
>> I'll look at fixing them up in my tree while Fred finishes his re-base.
>>
>> --
>> Alex Bennée
> Hi,
>
> Is that possible those one have been added since the V7 version?
> I saw some changes there.

My tree is based of your -wip branch (I called it -v8-wip). How is the
official re-base going?

>
> Thanks,
> Fred


--
Alex Bennée

Re: [Qemu-devel] Status of my hacks on the MTTCG WIP branch

[Alex Bennée]

Pranith Kumar <bobby.prani@gmail.com> writes:

> Hi Alex,
>
> On Tue, Jan 12, 2016 at 12:29 PM, Alex Bennée <alex.bennee@linaro.org>
> wrote:
>
>>
> https://github.com/stsquad/qemu/tree/mttcg/multi_tcg_v8_wip_ajb_fix_locks
>>
>
> I built this branch and ran an arm64 guest. It seems to be failing
> similarly to what I reported earlier:

Hi Pranith,

Can you try this branch:

https://github.com/stsquad/qemu/tree/mttcg/multi_tcg_v8_wip_ajb_fix_locks-r1

I think I've caught all the things likely to screw up addressing.

--
Alex Bennée

Re: [Qemu-devel] Status of my hacks on the MTTCG WIP branch

[Pranith Kumar]

[-- Attachment #1: Type: text/plain, Size: 3078 bytes --]

Hi Alex,

On Fri, Jan 15, 2016 at 8:53 AM, Alex Bennée <alex.bennee@linaro.org> wrote:
> Can you try this branch:
>
>
https://github.com/stsquad/qemu/tree/mttcg/multi_tcg_v8_wip_ajb_fix_locks-r1
>
> I think I've caught all the things likely to screw up addressing.
>

I tried this branch and the boot hangs like follows:

[    2.001083] random: systemd-udevd urandom read with 1 bits of entropy
available
main-loop: WARNING: I/O thread spun for 1000 iterations
[   23.778970] INFO: rcu_sched detected stalls on CPUs/tasks: {} (detected
by 0, t=2102 jiffies, g=-165, c=-166, q=83)
[   23.780265] All QSes seen, last rcu_sched kthread activity 2101
(4294939656-4294937555), jiffies_till_next_fqs=1, root ->qsmask 0x0
[   23.781228] swapper/0       R  running task        0     0      0
0x00000080
[   23.781977] Call trace:
[   23.782375] [<ffffffc00008a4cc>] dump_backtrace+0x0/0x170
[   23.782852] [<ffffffc00008a65c>] show_stack+0x20/0x2c
[   23.783279] [<ffffffc0000c6ba0>] sched_show_task+0x9c/0xf0
[   23.783746] [<ffffffc0000f244c>] rcu_check_callbacks+0x7b8/0x828
[   23.784230] [<ffffffc0000f75c4>] update_process_times+0x40/0x74
[   23.784723] [<ffffffc000107a60>] tick_sched_handle.isra.15+0x38/0x7c
[   23.785247] [<ffffffc000107aec>] tick_sched_timer+0x48/0x84
[   23.785705] [<ffffffc0000f7bb0>] __run_hrtimer+0x90/0x200
[   23.786148] [<ffffffc0000f874c>] hrtimer_interrupt+0xec/0x268
[   23.786612] [<ffffffc0003d9304>] arch_timer_handler_virt+0x38/0x48
[   23.787120] [<ffffffc0000e9ac4>] handle_percpu_devid_irq+0x90/0x12c
[   23.787621] [<ffffffc0000e53fc>] generic_handle_irq+0x38/0x54
[   23.788093] [<ffffffc0000e5744>] __handle_domain_irq+0x68/0xc4
[   23.788578] [<ffffffc000082478>] gic_handle_irq+0x38/0x84
[   23.789035] Exception stack(0xffffffc00073bde0 to 0xffffffc00073bf00)
[   23.789650] bde0: 00738000 ffffffc0 0073e71c ffffffc0 0073bf20 ffffffc0
00086948 ffffffc0
[   23.790356] be00: 000d848c ffffffc0 00000000 00000000 3ffcdb0c ffffffc0
00000000 01000000
[   23.791030] be20: 38b97100 ffffffc0 0073bea0 ffffffc0 67f6e000 00000005
567f1c33 00000000
[   23.791744] be40: 00748cf0 ffffffc0 0073be70 ffffffc0 c1e2e4a0 ffffffbd
3a801148 ffffffc0
[   23.792406] be60: 00000000 00000040 0073e000 ffffffc0 3a801168 ffffffc0
97bbb588 0000007f
[   23.793055] be80: 0021d7e8 ffffffc0 97b3d6ec 0000007f c37184d0 0000007f
00738000 ffffffc0
[   23.793720] bea0: 0073e71c ffffffc0 006ff7e8 ffffffc0 007c8000 ffffffc0
0073e680 ffffffc0
[   23.794373] bec0: 0072fac0 ffffffc0 00000001 00000000 0073bf30 ffffffc0
0050e9e8 ffffffc0
[   23.795025] bee0: 00000000 00000000 0073bf20 ffffffc0 00086944 ffffffc0
0073bf20 ffffffc0
[   23.795721] [<ffffffc0000855a4>] el1_irq+0x64/0xc0
[   23.796131] [<ffffffc0000d8488>] cpu_startup_entry+0x130/0x204
[   23.796605] [<ffffffc0004fba38>] rest_init+0x78/0x84
[   23.797028] [<ffffffc0006ca99c>] start_kernel+0x3a0/0x3b8
[   23.797528] rcu_sched kthread starved for 2101 jiffies!


I will try to debug and see where it is hanging.

Thanks!
-- 
Pranith

[-- Attachment #2: Type: text/html, Size: 3605 bytes --]

Re: [Qemu-devel] Status of my hacks on the MTTCG WIP branch

[KONRAD Frederic]

[-- Attachment #1: Type: text/plain, Size: 4054 bytes --]



Le 15/01/2016 15:24, Pranith Kumar a écrit :
> Hi Alex,
>
> On Fri, Jan 15, 2016 at 8:53 AM, Alex Bennée <alex.bennee@linaro.org 
> <mailto:alex.bennee@linaro.org>> wrote:
> > Can you try this branch:
> >
> > 
> https://github.com/stsquad/qemu/tree/mttcg/multi_tcg_v8_wip_ajb_fix_locks-r1
> >
> > I think I've caught all the things likely to screw up addressing.
> >
>
> I tried this branch and the boot hangs like follows:
>
> [    2.001083] random: systemd-udevd urandom read with 1 bits of 
> entropy available
> main-loop: WARNING: I/O thread spun for 1000 iterations
> [   23.778970] INFO: rcu_sched detected stalls on CPUs/tasks: {} 
> (detected by 0, t=2102 jiffies, g=-165, c=-166, q=83)
> [   23.780265] All QSes seen, last rcu_sched kthread activity 2101 
> (4294939656-4294937555), jiffies_till_next_fqs=1, root ->qsmask 0x0
> [   23.781228] swapper/0       R  running task        0 0      0 
> 0x00000080
> [   23.781977] Call trace:
> [   23.782375] [<ffffffc00008a4cc>] dump_backtrace+0x0/0x170
> [   23.782852] [<ffffffc00008a65c>] show_stack+0x20/0x2c
> [   23.783279] [<ffffffc0000c6ba0>] sched_show_task+0x9c/0xf0
> [   23.783746] [<ffffffc0000f244c>] rcu_check_callbacks+0x7b8/0x828
> [   23.784230] [<ffffffc0000f75c4>] update_process_times+0x40/0x74
> [   23.784723] [<ffffffc000107a60>] tick_sched_handle.isra.15+0x38/0x7c
> [   23.785247] [<ffffffc000107aec>] tick_sched_timer+0x48/0x84
> [   23.785705] [<ffffffc0000f7bb0>] __run_hrtimer+0x90/0x200
> [   23.786148] [<ffffffc0000f874c>] hrtimer_interrupt+0xec/0x268
> [   23.786612] [<ffffffc0003d9304>] arch_timer_handler_virt+0x38/0x48
> [   23.787120] [<ffffffc0000e9ac4>] handle_percpu_devid_irq+0x90/0x12c
> [   23.787621] [<ffffffc0000e53fc>] generic_handle_irq+0x38/0x54
> [   23.788093] [<ffffffc0000e5744>] __handle_domain_irq+0x68/0xc4
> [   23.788578] [<ffffffc000082478>] gic_handle_irq+0x38/0x84
> [   23.789035] Exception stack(0xffffffc00073bde0 to 0xffffffc00073bf00)
> [   23.789650] bde0: 00738000 ffffffc0 0073e71c ffffffc0 0073bf20 
> ffffffc0 00086948 ffffffc0
> [   23.790356] be00: 000d848c ffffffc0 00000000 00000000 3ffcdb0c 
> ffffffc0 00000000 01000000
> [   23.791030] be20: 38b97100 ffffffc0 0073bea0 ffffffc0 67f6e000 
> 00000005 567f1c33 00000000
> [   23.791744] be40: 00748cf0 ffffffc0 0073be70 ffffffc0 c1e2e4a0 
> ffffffbd 3a801148 ffffffc0
> [   23.792406] be60: 00000000 00000040 0073e000 ffffffc0 3a801168 
> ffffffc0 97bbb588 0000007f
> [   23.793055] be80: 0021d7e8 ffffffc0 97b3d6ec 0000007f c37184d0 
> 0000007f 00738000 ffffffc0
> [   23.793720] bea0: 0073e71c ffffffc0 006ff7e8 ffffffc0 007c8000 
> ffffffc0 0073e680 ffffffc0
> [   23.794373] bec0: 0072fac0 ffffffc0 00000001 00000000 0073bf30 
> ffffffc0 0050e9e8 ffffffc0
> [   23.795025] bee0: 00000000 00000000 0073bf20 ffffffc0 00086944 
> ffffffc0 0073bf20 ffffffc0
> [   23.795721] [<ffffffc0000855a4>] el1_irq+0x64/0xc0
> [   23.796131] [<ffffffc0000d8488>] cpu_startup_entry+0x130/0x204
> [   23.796605] [<ffffffc0004fba38>] rest_init+0x78/0x84
> [   23.797028] [<ffffffc0006ca99c>] start_kernel+0x3a0/0x3b8
> [   23.797528] rcu_sched kthread starved for 2101 jiffies!
>
>
> I will try to debug and see where it is hanging.
>
> Thanks!
> -- 
> Pranith

Hi Pranith,

I don't have time today to look into that.

But I missed a tb_find_physical which happen during tb_lock not held..
This hack should fix that (and probably slow things down):

diff --git a/cpu-exec.c b/cpu-exec.c
index 903126f..25a005a 100644
--- a/cpu-exec.c
+++ b/cpu-exec.c
@@ -252,9 +252,9 @@ static TranslationBlock *tb_find_physical(CPUState *cpu,
      }

      /* Move the TB to the head of the list */
-    *ptb1 = tb->phys_hash_next;
-    tb->phys_hash_next = tcg_ctx.tb_ctx.tb_phys_hash[h];
-    tcg_ctx.tb_ctx.tb_phys_hash[h] = tb;
+//    *ptb1 = tb->phys_hash_next;
+//    tb->phys_hash_next = tcg_ctx.tb_ctx.tb_phys_hash[h];
+//    tcg_ctx.tb_ctx.tb_phys_hash[h] = tb;
      return tb;
  }

Fred

[-- Attachment #2: Type: text/html, Size: 6464 bytes --]

Re: [Qemu-devel] Status of my hacks on the MTTCG WIP branch

[Alex Bennée]

KONRAD Frederic <fred.konrad@greensocs.com> writes:

> Le 15/01/2016 15:24, Pranith Kumar a écrit :
>> Hi Alex,
>>
>> On Fri, Jan 15, 2016 at 8:53 AM, Alex Bennée <alex.bennee@linaro.org
>> <mailto:alex.bennee@linaro.org>> wrote:
>> > Can you try this branch:
>> >
>> >
>> https://github.com/stsquad/qemu/tree/mttcg/multi_tcg_v8_wip_ajb_fix_locks-r1
>> >
>> > I think I've caught all the things likely to screw up addressing.
>> >
>>
>> I tried this branch and the boot hangs like follows:
>>
>> [    2.001083] random: systemd-udevd urandom read with 1 bits of
>> entropy available
>> main-loop: WARNING: I/O thread spun for 1000 iterations
>> [   23.778970] INFO: rcu_sched detected stalls on CPUs/tasks: {}
>> (detected by 0, t=2102 jiffies, g=-165, c=-166, q=83)
>> [   23.780265] All QSes seen, last rcu_sched kthread activity 2101
>> (4294939656-4294937555), jiffies_till_next_fqs=1, root ->qsmask 0x0
>> [   23.781228] swapper/0       R  running task        0 0      0
>> 0x00000080
>> [   23.781977] Call trace:
>> [   23.782375] [<ffffffc00008a4cc>] dump_backtrace+0x0/0x170
>> [   23.782852] [<ffffffc00008a65c>] show_stack+0x20/0x2c
>> [   23.783279] [<ffffffc0000c6ba0>] sched_show_task+0x9c/0xf0
>> [   23.783746] [<ffffffc0000f244c>] rcu_check_callbacks+0x7b8/0x828
>> [   23.784230] [<ffffffc0000f75c4>] update_process_times+0x40/0x74
>> [   23.784723] [<ffffffc000107a60>] tick_sched_handle.isra.15+0x38/0x7c
>> [   23.785247] [<ffffffc000107aec>] tick_sched_timer+0x48/0x84
>> [   23.785705] [<ffffffc0000f7bb0>] __run_hrtimer+0x90/0x200
>> [   23.786148] [<ffffffc0000f874c>] hrtimer_interrupt+0xec/0x268
>> [   23.786612] [<ffffffc0003d9304>] arch_timer_handler_virt+0x38/0x48
>> [   23.787120] [<ffffffc0000e9ac4>] handle_percpu_devid_irq+0x90/0x12c
>> [   23.787621] [<ffffffc0000e53fc>] generic_handle_irq+0x38/0x54
>> [   23.788093] [<ffffffc0000e5744>] __handle_domain_irq+0x68/0xc4
>> [   23.788578] [<ffffffc000082478>] gic_handle_irq+0x38/0x84
>> [   23.789035] Exception stack(0xffffffc00073bde0 to 0xffffffc00073bf00)
>> [   23.789650] bde0: 00738000 ffffffc0 0073e71c ffffffc0 0073bf20
>> ffffffc0 00086948 ffffffc0
>> [   23.790356] be00: 000d848c ffffffc0 00000000 00000000 3ffcdb0c
>> ffffffc0 00000000 01000000
>> [   23.791030] be20: 38b97100 ffffffc0 0073bea0 ffffffc0 67f6e000
>> 00000005 567f1c33 00000000
>> [   23.791744] be40: 00748cf0 ffffffc0 0073be70 ffffffc0 c1e2e4a0
>> ffffffbd 3a801148 ffffffc0
>> [   23.792406] be60: 00000000 00000040 0073e000 ffffffc0 3a801168
>> ffffffc0 97bbb588 0000007f
>> [   23.793055] be80: 0021d7e8 ffffffc0 97b3d6ec 0000007f c37184d0
>> 0000007f 00738000 ffffffc0
>> [   23.793720] bea0: 0073e71c ffffffc0 006ff7e8 ffffffc0 007c8000
>> ffffffc0 0073e680 ffffffc0
>> [   23.794373] bec0: 0072fac0 ffffffc0 00000001 00000000 0073bf30
>> ffffffc0 0050e9e8 ffffffc0
>> [   23.795025] bee0: 00000000 00000000 0073bf20 ffffffc0 00086944
>> ffffffc0 0073bf20 ffffffc0
>> [   23.795721] [<ffffffc0000855a4>] el1_irq+0x64/0xc0
>> [   23.796131] [<ffffffc0000d8488>] cpu_startup_entry+0x130/0x204
>> [   23.796605] [<ffffffc0004fba38>] rest_init+0x78/0x84
>> [   23.797028] [<ffffffc0006ca99c>] start_kernel+0x3a0/0x3b8
>> [   23.797528] rcu_sched kthread starved for 2101 jiffies!
>>
>>
>> I will try to debug and see where it is hanging.
>>
>> Thanks!
>> --
>> Pranith
>
> Hi Pranith,
>
> I don't have time today to look into that.
>
> But I missed a tb_find_physical which happen during tb_lock not held..
> This hack should fix that (and probably slow things down):
>
> diff --git a/cpu-exec.c b/cpu-exec.c
> index 903126f..25a005a 100644
> --- a/cpu-exec.c
> +++ b/cpu-exec.c
> @@ -252,9 +252,9 @@ static TranslationBlock *tb_find_physical(CPUState *cpu,
>       }
>
>       /* Move the TB to the head of the list */
> -    *ptb1 = tb->phys_hash_next;
> -    tb->phys_hash_next = tcg_ctx.tb_ctx.tb_phys_hash[h];
> -    tcg_ctx.tb_ctx.tb_phys_hash[h] = tb;
> +//    *ptb1 = tb->phys_hash_next;
> +//    tb->phys_hash_next = tcg_ctx.tb_ctx.tb_phys_hash[h];
> +//    tcg_ctx.tb_ctx.tb_phys_hash[h] = tb;
>       return tb;
>   }

Hmm not in my build cpu_exec:

                ...
                tb_lock();
                tb = tb_find_fast(cpu);
                ...

Which I think is right. I mean I can see if it wasn't then breakage
could occur when you manipulate the lookup but I think we should keep
the lock there and if it proves to be a performance hit come up with a
safe optimisation. I think Paolo talked about using RCU type locks.

--
Alex Bennée

Re: [Qemu-devel] Status of my hacks on the MTTCG WIP branch

[KONRAD Frederic]

Le 15/01/2016 15:46, Alex Bennée a écrit :
> KONRAD Frederic <fred.konrad@greensocs.com> writes:
>
>> Le 15/01/2016 15:24, Pranith Kumar a écrit :
>>> Hi Alex,
>>>
>>> On Fri, Jan 15, 2016 at 8:53 AM, Alex Bennée <alex.bennee@linaro.org
>>> <mailto:alex.bennee@linaro.org>> wrote:
>>>> Can you try this branch:
>>>>
>>>>
>>> https://github.com/stsquad/qemu/tree/mttcg/multi_tcg_v8_wip_ajb_fix_locks-r1
>>>> I think I've caught all the things likely to screw up addressing.
>>>>
>>> I tried this branch and the boot hangs like follows:
>>>
>>> [    2.001083] random: systemd-udevd urandom read with 1 bits of
>>> entropy available
>>> main-loop: WARNING: I/O thread spun for 1000 iterations
>>> [   23.778970] INFO: rcu_sched detected stalls on CPUs/tasks: {}
>>> (detected by 0, t=2102 jiffies, g=-165, c=-166, q=83)
>>> [   23.780265] All QSes seen, last rcu_sched kthread activity 2101
>>> (4294939656-4294937555), jiffies_till_next_fqs=1, root ->qsmask 0x0
>>> [   23.781228] swapper/0       R  running task        0 0      0
>>> 0x00000080
>>> [   23.781977] Call trace:
>>> [   23.782375] [<ffffffc00008a4cc>] dump_backtrace+0x0/0x170
>>> [   23.782852] [<ffffffc00008a65c>] show_stack+0x20/0x2c
>>> [   23.783279] [<ffffffc0000c6ba0>] sched_show_task+0x9c/0xf0
>>> [   23.783746] [<ffffffc0000f244c>] rcu_check_callbacks+0x7b8/0x828
>>> [   23.784230] [<ffffffc0000f75c4>] update_process_times+0x40/0x74
>>> [   23.784723] [<ffffffc000107a60>] tick_sched_handle.isra.15+0x38/0x7c
>>> [   23.785247] [<ffffffc000107aec>] tick_sched_timer+0x48/0x84
>>> [   23.785705] [<ffffffc0000f7bb0>] __run_hrtimer+0x90/0x200
>>> [   23.786148] [<ffffffc0000f874c>] hrtimer_interrupt+0xec/0x268
>>> [   23.786612] [<ffffffc0003d9304>] arch_timer_handler_virt+0x38/0x48
>>> [   23.787120] [<ffffffc0000e9ac4>] handle_percpu_devid_irq+0x90/0x12c
>>> [   23.787621] [<ffffffc0000e53fc>] generic_handle_irq+0x38/0x54
>>> [   23.788093] [<ffffffc0000e5744>] __handle_domain_irq+0x68/0xc4
>>> [   23.788578] [<ffffffc000082478>] gic_handle_irq+0x38/0x84
>>> [   23.789035] Exception stack(0xffffffc00073bde0 to 0xffffffc00073bf00)
>>> [   23.789650] bde0: 00738000 ffffffc0 0073e71c ffffffc0 0073bf20
>>> ffffffc0 00086948 ffffffc0
>>> [   23.790356] be00: 000d848c ffffffc0 00000000 00000000 3ffcdb0c
>>> ffffffc0 00000000 01000000
>>> [   23.791030] be20: 38b97100 ffffffc0 0073bea0 ffffffc0 67f6e000
>>> 00000005 567f1c33 00000000
>>> [   23.791744] be40: 00748cf0 ffffffc0 0073be70 ffffffc0 c1e2e4a0
>>> ffffffbd 3a801148 ffffffc0
>>> [   23.792406] be60: 00000000 00000040 0073e000 ffffffc0 3a801168
>>> ffffffc0 97bbb588 0000007f
>>> [   23.793055] be80: 0021d7e8 ffffffc0 97b3d6ec 0000007f c37184d0
>>> 0000007f 00738000 ffffffc0
>>> [   23.793720] bea0: 0073e71c ffffffc0 006ff7e8 ffffffc0 007c8000
>>> ffffffc0 0073e680 ffffffc0
>>> [   23.794373] bec0: 0072fac0 ffffffc0 00000001 00000000 0073bf30
>>> ffffffc0 0050e9e8 ffffffc0
>>> [   23.795025] bee0: 00000000 00000000 0073bf20 ffffffc0 00086944
>>> ffffffc0 0073bf20 ffffffc0
>>> [   23.795721] [<ffffffc0000855a4>] el1_irq+0x64/0xc0
>>> [   23.796131] [<ffffffc0000d8488>] cpu_startup_entry+0x130/0x204
>>> [   23.796605] [<ffffffc0004fba38>] rest_init+0x78/0x84
>>> [   23.797028] [<ffffffc0006ca99c>] start_kernel+0x3a0/0x3b8
>>> [   23.797528] rcu_sched kthread starved for 2101 jiffies!
>>>
>>>
>>> I will try to debug and see where it is hanging.
>>>
>>> Thanks!
>>> --
>>> Pranith
>> Hi Pranith,
>>
>> I don't have time today to look into that.
>>
>> But I missed a tb_find_physical which happen during tb_lock not held..
>> This hack should fix that (and probably slow things down):
>>
>> diff --git a/cpu-exec.c b/cpu-exec.c
>> index 903126f..25a005a 100644
>> --- a/cpu-exec.c
>> +++ b/cpu-exec.c
>> @@ -252,9 +252,9 @@ static TranslationBlock *tb_find_physical(CPUState *cpu,
>>        }
>>
>>        /* Move the TB to the head of the list */
>> -    *ptb1 = tb->phys_hash_next;
>> -    tb->phys_hash_next = tcg_ctx.tb_ctx.tb_phys_hash[h];
>> -    tcg_ctx.tb_ctx.tb_phys_hash[h] = tb;
>> +//    *ptb1 = tb->phys_hash_next;
>> +//    tb->phys_hash_next = tcg_ctx.tb_ctx.tb_phys_hash[h];
>> +//    tcg_ctx.tb_ctx.tb_phys_hash[h] = tb;
>>        return tb;
>>    }
> Hmm not in my build cpu_exec:
>
>                  ...
>                  tb_lock();
>                  tb = tb_find_fast(cpu);
>                  ...
>
> Which I think is right. I mean I can see if it wasn't then breakage
> could occur when you manipulate the lookup but I think we should keep
> the lock there and if it proves to be a performance hit come up with a
> safe optimisation. I think Paolo talked about using RCU type locks.
That's definitely a performance hit.
Ok we should talk about that Monday.

Fred
>
> --
> Alex Bennée

Re: [Qemu-devel] Status of my hacks on the MTTCG WIP branch

[Paolo Bonzini]

On 15/01/2016 15:49, KONRAD Frederic wrote:
> 
>        /* Move the TB to the head of the list */
> -    *ptb1 = tb->phys_hash_next;
> -    tb->phys_hash_next = tcg_ctx.tb_ctx.tb_phys_hash[h];
> -    tcg_ctx.tb_ctx.tb_phys_hash[h] = tb;
> +//    *ptb1 = tb->phys_hash_next;
> +//    tb->phys_hash_next = tcg_ctx.tb_ctx.tb_phys_hash[h];
> +//    tcg_ctx.tb_ctx.tb_phys_hash[h] = tb;

This is the right fix.  It's a *huge* performance hit to take the
tb_lock around tb_find_fast.

Paolo

Re: [Qemu-devel] Status of my hacks on the MTTCG WIP branch

[alvise rigo]

This problem could be related to a missing multi-threaded aware
translation of the atomic instructions.
I'm working on this missing piece, probably the next week I will
publish something.

Regards,
alvise

On Fri, Jan 15, 2016 at 3:24 PM, Pranith Kumar <bobby.prani@gmail.com> wrote:
> Hi Alex,
>
> On Fri, Jan 15, 2016 at 8:53 AM, Alex Bennée <alex.bennee@linaro.org> wrote:
>> Can you try this branch:
>>
>>
>> https://github.com/stsquad/qemu/tree/mttcg/multi_tcg_v8_wip_ajb_fix_locks-r1
>>
>> I think I've caught all the things likely to screw up addressing.
>>
>
> I tried this branch and the boot hangs like follows:
>
> [    2.001083] random: systemd-udevd urandom read with 1 bits of entropy
> available
> main-loop: WARNING: I/O thread spun for 1000 iterations
> [   23.778970] INFO: rcu_sched detected stalls on CPUs/tasks: {} (detected
> by 0, t=2102 jiffies, g=-165, c=-166, q=83)
> [   23.780265] All QSes seen, last rcu_sched kthread activity 2101
> (4294939656-4294937555), jiffies_till_next_fqs=1, root ->qsmask 0x0
> [   23.781228] swapper/0       R  running task        0     0      0
> 0x00000080
> [   23.781977] Call trace:
> [   23.782375] [<ffffffc00008a4cc>] dump_backtrace+0x0/0x170
> [   23.782852] [<ffffffc00008a65c>] show_stack+0x20/0x2c
> [   23.783279] [<ffffffc0000c6ba0>] sched_show_task+0x9c/0xf0
> [   23.783746] [<ffffffc0000f244c>] rcu_check_callbacks+0x7b8/0x828
> [   23.784230] [<ffffffc0000f75c4>] update_process_times+0x40/0x74
> [   23.784723] [<ffffffc000107a60>] tick_sched_handle.isra.15+0x38/0x7c
> [   23.785247] [<ffffffc000107aec>] tick_sched_timer+0x48/0x84
> [   23.785705] [<ffffffc0000f7bb0>] __run_hrtimer+0x90/0x200
> [   23.786148] [<ffffffc0000f874c>] hrtimer_interrupt+0xec/0x268
> [   23.786612] [<ffffffc0003d9304>] arch_timer_handler_virt+0x38/0x48
> [   23.787120] [<ffffffc0000e9ac4>] handle_percpu_devid_irq+0x90/0x12c
> [   23.787621] [<ffffffc0000e53fc>] generic_handle_irq+0x38/0x54
> [   23.788093] [<ffffffc0000e5744>] __handle_domain_irq+0x68/0xc4
> [   23.788578] [<ffffffc000082478>] gic_handle_irq+0x38/0x84
> [   23.789035] Exception stack(0xffffffc00073bde0 to 0xffffffc00073bf00)
> [   23.789650] bde0: 00738000 ffffffc0 0073e71c ffffffc0 0073bf20 ffffffc0
> 00086948 ffffffc0
> [   23.790356] be00: 000d848c ffffffc0 00000000 00000000 3ffcdb0c ffffffc0
> 00000000 01000000
> [   23.791030] be20: 38b97100 ffffffc0 0073bea0 ffffffc0 67f6e000 00000005
> 567f1c33 00000000
> [   23.791744] be40: 00748cf0 ffffffc0 0073be70 ffffffc0 c1e2e4a0 ffffffbd
> 3a801148 ffffffc0
> [   23.792406] be60: 00000000 00000040 0073e000 ffffffc0 3a801168 ffffffc0
> 97bbb588 0000007f
> [   23.793055] be80: 0021d7e8 ffffffc0 97b3d6ec 0000007f c37184d0 0000007f
> 00738000 ffffffc0
> [   23.793720] bea0: 0073e71c ffffffc0 006ff7e8 ffffffc0 007c8000 ffffffc0
> 0073e680 ffffffc0
> [   23.794373] bec0: 0072fac0 ffffffc0 00000001 00000000 0073bf30 ffffffc0
> 0050e9e8 ffffffc0
> [   23.795025] bee0: 00000000 00000000 0073bf20 ffffffc0 00086944 ffffffc0
> 0073bf20 ffffffc0
> [   23.795721] [<ffffffc0000855a4>] el1_irq+0x64/0xc0
> [   23.796131] [<ffffffc0000d8488>] cpu_startup_entry+0x130/0x204
> [   23.796605] [<ffffffc0004fba38>] rest_init+0x78/0x84
> [   23.797028] [<ffffffc0006ca99c>] start_kernel+0x3a0/0x3b8
> [   23.797528] rcu_sched kthread starved for 2101 jiffies!
>
>
> I will try to debug and see where it is hanging.
>
> Thanks!
> --
> Pranith

Re: [Qemu-devel] Status of my hacks on the MTTCG WIP branch

[Alex Bennée]

alvise rigo <a.rigo@virtualopensystems.com> writes:

> This problem could be related to a missing multi-threaded aware
> translation of the atomic instructions.
> I'm working on this missing piece, probably the next week I will
> publish something.

Maybe. We still have Fred's:

  Use atomic cmpxchg to atomically check the exclusive value in a STREX

Which I think papers over the cracks for both arm and aarch64 in MTTCG
while not being as correct as your work.

>
> Regards,
> alvise
>
> On Fri, Jan 15, 2016 at 3:24 PM, Pranith Kumar <bobby.prani@gmail.com> wrote:
>> Hi Alex,
>>
>> On Fri, Jan 15, 2016 at 8:53 AM, Alex Bennée <alex.bennee@linaro.org> wrote:
>>> Can you try this branch:
>>>
>>>
>>> https://github.com/stsquad/qemu/tree/mttcg/multi_tcg_v8_wip_ajb_fix_locks-r1
>>>
>>> I think I've caught all the things likely to screw up addressing.
>>>
>>
>> I tried this branch and the boot hangs like follows:
>>
>> [    2.001083] random: systemd-udevd urandom read with 1 bits of entropy
>> available
>> main-loop: WARNING: I/O thread spun for 1000 iterations
>> [   23.778970] INFO: rcu_sched detected stalls on CPUs/tasks: {} (detected
>> by 0, t=2102 jiffies, g=-165, c=-166, q=83)

This is just saying the kernel has been waiting for a while and nothing
has happened.

>> I will try to debug and see where it is hanging.

If we knew what the kernel was waiting for that would be useful to know.

>>
>> Thanks!
>> --
>> Pranith


--
Alex Bennée

Re: [Qemu-devel] Status of my hacks on the MTTCG WIP branch

[alvise rigo]

On Fri, Jan 15, 2016 at 3:51 PM, Alex Bennée <alex.bennee@linaro.org> wrote:
>
> alvise rigo <a.rigo@virtualopensystems.com> writes:
>
>> This problem could be related to a missing multi-threaded aware
>> translation of the atomic instructions.
>> I'm working on this missing piece, probably the next week I will
>> publish something.
>
> Maybe. We still have Fred's:
>
>   Use atomic cmpxchg to atomically check the exclusive value in a STREX
>
> Which I think papers over the cracks for both arm and aarch64 in MTTCG
> while not being as correct as your work.

Keep in mind that Linux on arm64 uses the LDXP/STXP instructions that
exist solely in aarch64.
These instructions are purely emulated now and can potentially write
128 bits of data in a non-atomic fashion.

Regards,
alvise

>
>>
>> Regards,
>> alvise
>>
>> On Fri, Jan 15, 2016 at 3:24 PM, Pranith Kumar <bobby.prani@gmail.com> wrote:
>>> Hi Alex,
>>>
>>> On Fri, Jan 15, 2016 at 8:53 AM, Alex Bennée <alex.bennee@linaro.org> wrote:
>>>> Can you try this branch:
>>>>
>>>>
>>>> https://github.com/stsquad/qemu/tree/mttcg/multi_tcg_v8_wip_ajb_fix_locks-r1
>>>>
>>>> I think I've caught all the things likely to screw up addressing.
>>>>
>>>
>>> I tried this branch and the boot hangs like follows:
>>>
>>> [    2.001083] random: systemd-udevd urandom read with 1 bits of entropy
>>> available
>>> main-loop: WARNING: I/O thread spun for 1000 iterations
>>> [   23.778970] INFO: rcu_sched detected stalls on CPUs/tasks: {} (detected
>>> by 0, t=2102 jiffies, g=-165, c=-166, q=83)
>
> This is just saying the kernel has been waiting for a while and nothing
> has happened.
>
>>> I will try to debug and see where it is hanging.
>
> If we knew what the kernel was waiting for that would be useful to know.
>
>>>
>>> Thanks!
>>> --
>>> Pranith
>
>
> --
> Alex Bennée

Re: [Qemu-devel] Status of my hacks on the MTTCG WIP branch

[Alex Bennée]

alvise rigo <a.rigo@virtualopensystems.com> writes:

> On Fri, Jan 15, 2016 at 3:51 PM, Alex Bennée <alex.bennee@linaro.org> wrote:
>>
>> alvise rigo <a.rigo@virtualopensystems.com> writes:
>>
>>> This problem could be related to a missing multi-threaded aware
>>> translation of the atomic instructions.
>>> I'm working on this missing piece, probably the next week I will
>>> publish something.
>>
>> Maybe. We still have Fred's:
>>
>>   Use atomic cmpxchg to atomically check the exclusive value in a STREX
>>
>> Which I think papers over the cracks for both arm and aarch64 in MTTCG
>> while not being as correct as your work.
>
> Keep in mind that Linux on arm64 uses the LDXP/STXP instructions that
> exist solely in aarch64.
> These instructions are purely emulated now and can potentially write
> 128 bits of data in a non-atomic fashion.

Sure, but I doubt they are the reason for this hang as the kernel
doesn't use them.

>
> Regards,
> alvise
>
>>
>>>
>>> Regards,
>>> alvise
>>>
>>> On Fri, Jan 15, 2016 at 3:24 PM, Pranith Kumar <bobby.prani@gmail.com> wrote:
>>>> Hi Alex,
>>>>
>>>> On Fri, Jan 15, 2016 at 8:53 AM, Alex Bennée <alex.bennee@linaro.org> wrote:
>>>>> Can you try this branch:
>>>>>
>>>>>
>>>>> https://github.com/stsquad/qemu/tree/mttcg/multi_tcg_v8_wip_ajb_fix_locks-r1
>>>>>
>>>>> I think I've caught all the things likely to screw up addressing.
>>>>>
>>>>
>>>> I tried this branch and the boot hangs like follows:
>>>>
>>>> [    2.001083] random: systemd-udevd urandom read with 1 bits of entropy
>>>> available
>>>> main-loop: WARNING: I/O thread spun for 1000 iterations
>>>> [   23.778970] INFO: rcu_sched detected stalls on CPUs/tasks: {} (detected
>>>> by 0, t=2102 jiffies, g=-165, c=-166, q=83)
>>
>> This is just saying the kernel has been waiting for a while and nothing
>> has happened.
>>
>>>> I will try to debug and see where it is hanging.
>>
>> If we knew what the kernel was waiting for that would be useful to know.
>>
>>>>
>>>> Thanks!
>>>> --
>>>> Pranith
>>
>>
>> --
>> Alex Bennée


--
Alex Bennée

Re: [Qemu-devel] Status of my hacks on the MTTCG WIP branch

[alvise rigo]

On Fri, Jan 15, 2016 at 4:25 PM, Alex Bennée <alex.bennee@linaro.org> wrote:
>
> alvise rigo <a.rigo@virtualopensystems.com> writes:
>
>> On Fri, Jan 15, 2016 at 3:51 PM, Alex Bennée <alex.bennee@linaro.org> wrote:
>>>
>>> alvise rigo <a.rigo@virtualopensystems.com> writes:
>>>
>>>> This problem could be related to a missing multi-threaded aware
>>>> translation of the atomic instructions.
>>>> I'm working on this missing piece, probably the next week I will
>>>> publish something.
>>>
>>> Maybe. We still have Fred's:
>>>
>>>   Use atomic cmpxchg to atomically check the exclusive value in a STREX
>>>
>>> Which I think papers over the cracks for both arm and aarch64 in MTTCG
>>> while not being as correct as your work.
>>
>> Keep in mind that Linux on arm64 uses the LDXP/STXP instructions that
>> exist solely in aarch64.
>> These instructions are purely emulated now and can potentially write
>> 128 bits of data in a non-atomic fashion.
>
> Sure, but I doubt they are the reason for this hang as the kernel
> doesn't use them.

The kernel does use them for __cmpxchg_double in
arch/arm64/include/asm/atomic_ll_sc.h.
In any case, the normal exclusive instructions are also emulated in
target-arm/translate-a64.c.

alvise

>
>>
>> Regards,
>> alvise
>>
>>>
>>>>
>>>> Regards,
>>>> alvise
>>>>
>>>> On Fri, Jan 15, 2016 at 3:24 PM, Pranith Kumar <bobby.prani@gmail.com> wrote:
>>>>> Hi Alex,
>>>>>
>>>>> On Fri, Jan 15, 2016 at 8:53 AM, Alex Bennée <alex.bennee@linaro.org> wrote:
>>>>>> Can you try this branch:
>>>>>>
>>>>>>
>>>>>> https://github.com/stsquad/qemu/tree/mttcg/multi_tcg_v8_wip_ajb_fix_locks-r1
>>>>>>
>>>>>> I think I've caught all the things likely to screw up addressing.
>>>>>>
>>>>>
>>>>> I tried this branch and the boot hangs like follows:
>>>>>
>>>>> [    2.001083] random: systemd-udevd urandom read with 1 bits of entropy
>>>>> available
>>>>> main-loop: WARNING: I/O thread spun for 1000 iterations
>>>>> [   23.778970] INFO: rcu_sched detected stalls on CPUs/tasks: {} (detected
>>>>> by 0, t=2102 jiffies, g=-165, c=-166, q=83)
>>>
>>> This is just saying the kernel has been waiting for a while and nothing
>>> has happened.
>>>
>>>>> I will try to debug and see where it is hanging.
>>>
>>> If we knew what the kernel was waiting for that would be useful to know.
>>>
>>>>>
>>>>> Thanks!
>>>>> --
>>>>> Pranith
>>>
>>>
>>> --
>>> Alex Bennée
>
>
> --
> Alex Bennée

Re: [Qemu-devel] Status of my hacks on the MTTCG WIP branch

[Alex Bennée]

alvise rigo <a.rigo@virtualopensystems.com> writes:

> On Fri, Jan 15, 2016 at 4:25 PM, Alex Bennée <alex.bennee@linaro.org> wrote:
>>
>> alvise rigo <a.rigo@virtualopensystems.com> writes:
>>
>>> On Fri, Jan 15, 2016 at 3:51 PM, Alex Bennée <alex.bennee@linaro.org> wrote:
>>>>
>>>> alvise rigo <a.rigo@virtualopensystems.com> writes:
>>>>
>>>>> This problem could be related to a missing multi-threaded aware
>>>>> translation of the atomic instructions.
>>>>> I'm working on this missing piece, probably the next week I will
>>>>> publish something.
>>>>
>>>> Maybe. We still have Fred's:
>>>>
>>>>   Use atomic cmpxchg to atomically check the exclusive value in a STREX
>>>>
>>>> Which I think papers over the cracks for both arm and aarch64 in MTTCG
>>>> while not being as correct as your work.
>>>
>>> Keep in mind that Linux on arm64 uses the LDXP/STXP instructions that
>>> exist solely in aarch64.
>>> These instructions are purely emulated now and can potentially write
>>> 128 bits of data in a non-atomic fashion.
>>
>> Sure, but I doubt they are the reason for this hang as the kernel
>> doesn't use them.
>
> The kernel does use them for __cmpxchg_double in
> arch/arm64/include/asm/atomic_ll_sc.h.

I take it back, if I'd have grepped for "ldxp" instead of "stxp" I would
have seen it, sorry about that ;-)

> In any case, the normal exclusive instructions are also emulated in
> target-arm/translate-a64.c.

I'll check on them on Monday. I'd assumed all the stuff was in the
helpers as I scanned through and missed the translate.c changes Fred
made. Hopefully that will be the last hurdle.

In the meantime if I'm not booting Jessie I can get MTTCG aarch64
working with a initrd based rootfs. Once I've gone through those I'm
planning on giving it a good stress test with -fsantize=threads.

>
> alvise
>
>>
>>>
>>> Regards,
>>> alvise
>>>
>>>>
>>>>>
>>>>> Regards,
>>>>> alvise
>>>>>
>>>>> On Fri, Jan 15, 2016 at 3:24 PM, Pranith Kumar <bobby.prani@gmail.com> wrote:
>>>>>> Hi Alex,
>>>>>>
>>>>>> On Fri, Jan 15, 2016 at 8:53 AM, Alex Bennée <alex.bennee@linaro.org> wrote:
>>>>>>> Can you try this branch:
>>>>>>>
>>>>>>>
>>>>>>> https://github.com/stsquad/qemu/tree/mttcg/multi_tcg_v8_wip_ajb_fix_locks-r1
>>>>>>>
>>>>>>> I think I've caught all the things likely to screw up addressing.
>>>>>>>
>>>>>>
>>>>>> I tried this branch and the boot hangs like follows:
>>>>>>
>>>>>> [    2.001083] random: systemd-udevd urandom read with 1 bits of entropy
>>>>>> available
>>>>>> main-loop: WARNING: I/O thread spun for 1000 iterations
>>>>>> [   23.778970] INFO: rcu_sched detected stalls on CPUs/tasks: {} (detected
>>>>>> by 0, t=2102 jiffies, g=-165, c=-166, q=83)
>>>>
>>>> This is just saying the kernel has been waiting for a while and nothing
>>>> has happened.
>>>>
>>>>>> I will try to debug and see where it is hanging.
>>>>
>>>> If we knew what the kernel was waiting for that would be useful to know.
>>>>
>>>>>>
>>>>>> Thanks!
>>>>>> --
>>>>>> Pranith
>>>>
>>>>
>>>> --
>>>> Alex Bennée
>>
>>
>> --
>> Alex Bennée


--
Alex Bennée

Re: [Qemu-devel] Status of my hacks on the MTTCG WIP branch

[Alex Bennée]

Alex Bennée <alex.bennee@linaro.org> writes:

> alvise rigo <a.rigo@virtualopensystems.com> writes:
>
>> On Fri, Jan 15, 2016 at 4:25 PM, Alex Bennée <alex.bennee@linaro.org> wrote:
>>>
>>> alvise rigo <a.rigo@virtualopensystems.com> writes:
>>>
>>>> On Fri, Jan 15, 2016 at 3:51 PM, Alex Bennée <alex.bennee@linaro.org> wrote:
>>>>>
>>>>> alvise rigo <a.rigo@virtualopensystems.com> writes:
>>>>>
<snip>
>>>> Keep in mind that Linux on arm64 uses the LDXP/STXP instructions that
>>>> exist solely in aarch64.
>>>> These instructions are purely emulated now and can potentially write
>>>> 128 bits of data in a non-atomic fashion.
>>>
>>> Sure, but I doubt they are the reason for this hang as the kernel
>>> doesn't use them.
>>
>> The kernel does use them for __cmpxchg_double in
>> arch/arm64/include/asm/atomic_ll_sc.h.
>
> I take it back, if I'd have grepped for "ldxp" instead of "stxp" I would
> have seen it, sorry about that ;-)
>
>> In any case, the normal exclusive instructions are also emulated in
>> target-arm/translate-a64.c.
>
> I'll check on them on Monday. I'd assumed all the stuff was in the
> helpers as I scanned through and missed the translate.c changes Fred
> made. Hopefully that will be the last hurdle.

I'm pleased to confirm you were right. I hacked up Fred's helper based
solution for aarch64 including the ldxp/stxp stuff. It's not
semantically correct because:

  result = atomic_bool_cmpxchg(p, oldval, (uint8_t)newval) &&
           atomic_bool_cmpxchg(&p[1], oldval2, (uint8_t)newval2);

won't leave the system as it was before if the race causes the second
cmpxchg to fail. I assume this won't be a problem in the LL/SC world as
we'll be able to serialise all accesses to the exclusive page properly?

See:

https://github.com/stsquad/qemu/tree/mttcg/multi_tcg_v8_wip_ajb_fix_locks-r2

>
> In the meantime if I'm not booting Jessie I can get MTTCG aarch64
> working with a initrd based rootfs. Once I've gone through those I'm
> planning on giving it a good stress test with -fsantize=threads.

My first pass with this threw up a bunch of errors with the RCU code
like this:

WARNING: ThreadSanitizer: data race (pid=15387)
  Atomic write of size 4 at 0x7f59efa51d48 by main thread (mutexes: write M172):
    #0 __tsan_atomic32_fetch_add <null> (libtsan.so.0+0x000000058e8f)
    #1 call_rcu1 util/rcu.c:288 (qemu-system-aarch64+0x0000006c3bd0)
    #2 address_space_update_topology /home/alex/lsrc/qemu/qemu.git/memory.c:806 (qemu-system-aarch64+0x0000001ed9ca)
    #3 memory_region_transaction_commit /home/alex/lsrc/qemu/qemu.git/memory.c:842 (qemu-system-aarch64+0x0000001ed9ca)
    #4 address_space_init /home/alex/lsrc/qemu/qemu.git/memory.c:2136 (qemu-system-aarch64+0x0000001f1fa6)
    #5 memory_map_init /home/alex/lsrc/qemu/qemu.git/exec.c:2344 (qemu-system-aarch64+0x000000196607)
    #6 cpu_exec_init_all /home/alex/lsrc/qemu/qemu.git/exec.c:2795 (qemu-system-aarch64+0x000000196607)
    #7 main /home/alex/lsrc/qemu/qemu.git/vl.c:4083 (qemu-system-aarch64+0x0000001829aa)

  Previous read of size 4 at 0x7f59efa51d48 by thread T1:
    #0 call_rcu_thread util/rcu.c:242 (qemu-system-aarch64+0x0000006c3d92)
    #1 <null> <null> (libtsan.so.0+0x0000000235f9)

  Location is global 'rcu_call_count' of size 4 at 0x7f59efa51d48 (qemu-system-aarch64+0x0000010f1d48)

  Mutex M172 (0x7f59ef6254e0) created at:
    #0 pthread_mutex_init <null> (libtsan.so.0+0x000000027ee5)
    #1 qemu_mutex_init util/qemu-thread-posix.c:55 (qemu-system-aarch64+0x0000006ad747)
    #2 qemu_init_cpu_loop /home/alex/lsrc/qemu/qemu.git/cpus.c:890 (qemu-system-aarch64+0x0000001d4166)
    #3 main /home/alex/lsrc/qemu/qemu.git/vl.c:3005 (qemu-system-aarch64+0x0000001820ac)

  Thread T1 (tid=15389, running) created by main thread at:
    #0 pthread_create <null> (libtsan.so.0+0x0000000274c7)
    #1 qemu_thread_create util/qemu-thread-posix.c:525 (qemu-system-aarch64+0x0000006ae04d)
    #2 rcu_init_complete util/rcu.c:320 (qemu-system-aarch64+0x0000006c3d52)
    #3 rcu_init util/rcu.c:351 (qemu-system-aarch64+0x00000018e288)
    #4 __libc_csu_init <null> (qemu-system-aarch64+0x0000006c63ec)


but I don't know how many are false positives so I'm going to look in more
detail now.

<snip>

--
Alex Bennée

Re: [Qemu-devel] Status of my hacks on the MTTCG WIP branch

[alvise rigo]

On Mon, Jan 18, 2016 at 8:09 PM, Alex Bennée <alex.bennee@linaro.org> wrote:
>
>
> Alex Bennée <alex.bennee@linaro.org> writes:
>
> > alvise rigo <a.rigo@virtualopensystems.com> writes:
> >
> >> On Fri, Jan 15, 2016 at 4:25 PM, Alex Bennée <alex.bennee@linaro.org> wrote:
> >>>
> >>> alvise rigo <a.rigo@virtualopensystems.com> writes:
> >>>
> >>>> On Fri, Jan 15, 2016 at 3:51 PM, Alex Bennée <alex.bennee@linaro.org> wrote:
> >>>>>
> >>>>> alvise rigo <a.rigo@virtualopensystems.com> writes:
> >>>>>
> <snip>
> >>>> Keep in mind that Linux on arm64 uses the LDXP/STXP instructions that
> >>>> exist solely in aarch64.
> >>>> These instructions are purely emulated now and can potentially write
> >>>> 128 bits of data in a non-atomic fashion.
> >>>
> >>> Sure, but I doubt they are the reason for this hang as the kernel
> >>> doesn't use them.
> >>
> >> The kernel does use them for __cmpxchg_double in
> >> arch/arm64/include/asm/atomic_ll_sc.h.
> >
> > I take it back, if I'd have grepped for "ldxp" instead of "stxp" I would
> > have seen it, sorry about that ;-)
> >
> >> In any case, the normal exclusive instructions are also emulated in
> >> target-arm/translate-a64.c.
> >
> > I'll check on them on Monday. I'd assumed all the stuff was in the
> > helpers as I scanned through and missed the translate.c changes Fred
> > made. Hopefully that will be the last hurdle.
>
> I'm pleased to confirm you were right. I hacked up Fred's helper based
> solution for aarch64 including the ldxp/stxp stuff. It's not
> semantically correct because:
>
>   result = atomic_bool_cmpxchg(p, oldval, (uint8_t)newval) &&
>            atomic_bool_cmpxchg(&p[1], oldval2, (uint8_t)newval2);
>
> won't leave the system as it was before if the race causes the second

Exactly.

> cmpxchg to fail. I assume this won't be a problem in the LL/SC world as
> we'll be able to serialise all accesses to the exclusive page properly?

In LL/SC the idea would be to dedicate one ARM-specific helper (in
target-arm/helper-a64.c) to handle this case.
Once the helper grabbed the excl mutex, we are allowed to make 128
bits or bigger accesses.

>
>
> See:
>
> https://github.com/stsquad/qemu/tree/mttcg/multi_tcg_v8_wip_ajb_fix_locks-r2
>
> >
> > In the meantime if I'm not booting Jessie I can get MTTCG aarch64
> > working with a initrd based rootfs. Once I've gone through those I'm
> > planning on giving it a good stress test with -fsantize=threads.
>
> My first pass with this threw up a bunch of errors with the RCU code
> like this:
>
> WARNING: ThreadSanitizer: data race (pid=15387)
>   Atomic write of size 4 at 0x7f59efa51d48 by main thread (mutexes: write M172):
>     #0 __tsan_atomic32_fetch_add <null> (libtsan.so.0+0x000000058e8f)
>     #1 call_rcu1 util/rcu.c:288 (qemu-system-aarch64+0x0000006c3bd0)
>     #2 address_space_update_topology /home/alex/lsrc/qemu/qemu.git/memory.c:806 (qemu-system-aarch64+0x0000001ed9ca)
>     #3 memory_region_transaction_commit /home/alex/lsrc/qemu/qemu.git/memory.c:842 (qemu-system-aarch64+0x0000001ed9ca)
>     #4 address_space_init /home/alex/lsrc/qemu/qemu.git/memory.c:2136 (qemu-system-aarch64+0x0000001f1fa6)
>     #5 memory_map_init /home/alex/lsrc/qemu/qemu.git/exec.c:2344 (qemu-system-aarch64+0x000000196607)
>     #6 cpu_exec_init_all /home/alex/lsrc/qemu/qemu.git/exec.c:2795 (qemu-system-aarch64+0x000000196607)
>     #7 main /home/alex/lsrc/qemu/qemu.git/vl.c:4083 (qemu-system-aarch64+0x0000001829aa)
>
>   Previous read of size 4 at 0x7f59efa51d48 by thread T1:
>     #0 call_rcu_thread util/rcu.c:242 (qemu-system-aarch64+0x0000006c3d92)
>     #1 <null> <null> (libtsan.so.0+0x0000000235f9)
>
>   Location is global 'rcu_call_count' of size 4 at 0x7f59efa51d48 (qemu-system-aarch64+0x0000010f1d48)
>
>   Mutex M172 (0x7f59ef6254e0) created at:
>     #0 pthread_mutex_init <null> (libtsan.so.0+0x000000027ee5)
>     #1 qemu_mutex_init util/qemu-thread-posix.c:55 (qemu-system-aarch64+0x0000006ad747)
>     #2 qemu_init_cpu_loop /home/alex/lsrc/qemu/qemu.git/cpus.c:890 (qemu-system-aarch64+0x0000001d4166)
>     #3 main /home/alex/lsrc/qemu/qemu.git/vl.c:3005 (qemu-system-aarch64+0x0000001820ac)
>
>   Thread T1 (tid=15389, running) created by main thread at:
>     #0 pthread_create <null> (libtsan.so.0+0x0000000274c7)
>     #1 qemu_thread_create util/qemu-thread-posix.c:525 (qemu-system-aarch64+0x0000006ae04d)
>     #2 rcu_init_complete util/rcu.c:320 (qemu-system-aarch64+0x0000006c3d52)
>     #3 rcu_init util/rcu.c:351 (qemu-system-aarch64+0x00000018e288)
>     #4 __libc_csu_init <null> (qemu-system-aarch64+0x0000006c63ec)
>
>
> but I don't know how many are false positives so I'm going to look in more
> detail now.

Umm...I'm not very familiar with the sanitize option, I'll let you
follow this lead :).

alvise

>
> <snip>
>
> --
> Alex Bennée