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SubjectRe: 07cde313b2 ("x86/msr: Allow rdmsr_safe_on_cpu() to schedule"): BUG: kernel hang in boot stage
On Tue, Mar 27, 2018 at 3:26 PM kernel test robot <fengguang.wu@intel.com>
wrote:

> Greetings,

> 0day kernel testing robot got the below dmesg and the first bad commit is

> https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/cleanups

> commit 07cde313b2d21f728cec2836db7cdb55476f7a26
> Author: Eric Dumazet <edumazet@google.com>
> AuthorDate: Fri Mar 23 14:58:17 2018 -0700
> Commit: Thomas Gleixner <tglx@linutronix.de>
> CommitDate: Tue Mar 27 12:01:47 2018 +0200

> x86/msr: Allow rdmsr_safe_on_cpu() to schedule

> High latencies can be observed caused by a daemon periodically reading
> various MSR on all cpus. On KASAN enabled kernels ~10ms latencies can
be
> observed simply reading one MSR. Even without KASAN, sending an IPI
to a
> CPU, which is in a deep sleep state or in a long hard IRQ disabled
section,
> waiting for the answer can consume hundreds of microseconds.

> All usage sites are in preemptible context, convert
rdmsr_safe_on_cpu() to
> use a completion instead of busy polling.

> Overall daemon cpu usage was reduced by 35 %, and latencies caused by
> msr_read() disappeared.

> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Acked-by: Ingo Molnar <mingo@kernel.org>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Eric Dumazet <eric.dumazet@gmail.com>
> Link:
https://lkml.kernel.org/r/20180323215818.127774-1-edumazet@google.com

> 13cc36d76b x86/rtc: Stop using deprecated functions
> 07cde313b2 x86/msr: Allow rdmsr_safe_on_cpu() to schedule
> 67bbd7a8d6 x86/cpuid: Allow cpuid_read() to schedule
> 990d052537 Merge branch 'x86/mm'

+-------------------------------+------------+------------+------------+------------+
> | | 13cc36d76b | 07cde313b2 | 67bbd7a8d6 |
990d052537 |

+-------------------------------+------------+------------+------------+------------+
> | boot_successes | 33 | 4 | 2 |
4 |
> | boot_failures | 0 | 11 | 15 |
11 |
> | BUG:kernel_hang_in_boot_stage | 0 | 11 | 13 |
11 |
> | BUG:kernel_in_stage | 0 | 0 | 2 |
|

+-------------------------------+------------+------------+------------+------------+

> [ 14.950320] fmc_trivial: probe of fake-design-for-testing-f001 failed
with error -95
> [ 14.953048] fmc fake-design-for-testing-f001: Driver has no ID:
matches all
> [ 14.955084] fmc_write_eeprom fake-design-for-testing-f001:
fmc_write_eeprom: no busid passed, refusing all cards
> [ 14.958301] fmc fake-design-for-testing-f001: Driver has no ID:
matches all
> [ 14.960428] fmc_chardev fake-design-for-testing-f001: Created misc
device "fake-design-for-testing-f001"
> BUG: kernel hang in boot stage


> # HH:MM RESULT
GOOD BAD GOOD_BUT_DIRTY DIRTY_NOT_BAD
> git bisect start c98e6b78ee92a4c5662febce64591980d77bd6c6
3eb2ce825ea1ad89d20f7a3b5780df850e4be274 --
> git bisect bad 110c6c42e12d406bf2e5c15e71023ed2e91cb17d # 01:31 B
0 11 24 0 Merge
'linux-review/Alex-Williamson/MAINTAINERS-vfio-platform-Update-sub-maintainer/20180327-143800'
into devel-spot-201803272204
> git bisect good ec45958cf484f5c9310df39d9f85dd43c22ae799 # 01:47 G
11 0 2 2 Merge 'slave-dma/next' into devel-spot-201803272204
> git bisect good 7103b9adcdc2a848c54f3afa4ab7730f420f3fe0 # 02:18 G
11 0 1 1 Merge
'linux-review/Emmanuel-Grumbach/mac80211-don-t-WARN-on-bad-WMM-parameters-from-buggy-APs/20180327-180036'
into devel-spot-201803272204
> git bisect bad ccf31c36bad5be0c7fbd4ce6e82b4410a7478da9 # 02:41 B
0 11 25 0 Merge 'wireless-drivers-next/master' into
devel-spot-201803272204
> git bisect bad 2105e74ef7120fa7b12d5c571763c0f6d06a75e9 # 03:02 B
0 9 22 0 Merge 'pza/reset/next' into devel-spot-201803272204
> git bisect bad 9a76dd69d30110dcecf0716dc961c93349da942b # 03:22 B
0 4 19 1 Merge
'linux-review/Vijendar-Mukunda/ASoC-dwc-I2S-Controller-instance-param-added/20180327-175125'
into devel-spot-201803272204
> git bisect bad ed6c6d580da3d088d4c3cb449e1bf3fbb4a6d66a # 03:44 B
0 5 19 0 Merge 'tip/x86/cleanups' into devel-spot-201803272204
> git bisect good 16d1cb0bc43642a4d934631a73c5210ad2499e2f # 04:08 G
11 0 0 0 x86/dumpstack: Unify show_regs()
> git bisect bad 07cde313b2d21f728cec2836db7cdb55476f7a26 # 04:26 B
0 5 19 0 x86/msr: Allow rdmsr_safe_on_cpu() to schedule
> git bisect good 13cc36d76bc4f5a9801ae32630bc8240ba0cc522 # 04:46 G
11 0 0 0 x86/rtc: Stop using deprecated functions
> # first bad commit: [07cde313b2d21f728cec2836db7cdb55476f7a26] x86/msr:
Allow rdmsr_safe_on_cpu() to schedule
> git bisect good 13cc36d76bc4f5a9801ae32630bc8240ba0cc522 # 04:51 G
31 0 2 2 x86/rtc: Stop using deprecated functions
> # extra tests with debug options
> git bisect bad 07cde313b2d21f728cec2836db7cdb55476f7a26 # 05:14 B
0 1 16 2 x86/msr: Allow rdmsr_safe_on_cpu() to schedule
> # extra tests on HEAD of linux-devel/devel-spot-201803272204
> git bisect bad c98e6b78ee92a4c5662febce64591980d77bd6c6 # 05:19 B
0 27 50 4 0day head guard for 'devel-spot-201803272204'
> # extra tests on tree/branch tip/x86/cleanups
> git bisect bad 67bbd7a8d6bcdc44cc27105ae8c374e9176ceaf1 # 05:47 B
0 7 23 2 x86/cpuid: Allow cpuid_read() to schedule
> # extra tests with first bad commit reverted
> git bisect good c885db74ec7feacddf4cce667615504892b756c8 # 06:05 G
11 0 1 1 Revert "x86/msr: Allow rdmsr_safe_on_cpu() to schedule"
> # extra tests on tree/branch tip/master
> git bisect bad 990d0525372f3f3bb5abcc527c8bb56a030c2b29 # 06:25 B
0 11 25 0 Merge branch 'x86/mm'

> ---
> 0-DAY kernel test infrastructure Open Source Technology
Center
> https://lists.01.org/pipermail/lkp Intel
Corporation

Thanks for the report.

Presumably the issue is that __rdmsr_safe_on_cpu() is also called from
rdmsrl_safe_on_cpu()

So we need to initialize the completion properly from this call site.

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