Discussion:
[x86/cpufeature] 7b5e74e637: BUG: unable to handle kernel paging request at 6b636170
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Ingo Molnar
2016-05-25 06:28:15 UTC
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0day kernel testing robot got the below dmesg and the first bad commit is
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
commit 7b5e74e637e4a977c7cf40fd7de332f60b68180e
AuthorDate: Tue Mar 29 17:41:54 2016 +0200
CommitDate: Thu Mar 31 13:33:17 2016 +0200
x86/cpufeature: Remove cpu_has_arch_perfmon
Use boot_cpu_has() instead.
This seem an unlikely candidate given...
[ 1.914984] random: trinity urandom read with 25 bits of entropy available
[ 8.542178] random: nonblocking pool is initialized
[ 11.939833] sock: process `trinity-main' is using obsolete setsockopt SO_BSDCOMPAT
[ 12.349890] BUG: unable to handle kernel paging request at 6b636170
[ 12.349895] IP: [<c108154b>] perf_prepare_sample+0x7d/0x263
The trace is more related to perf.
Also, 7b5e74e637e4a appears to be pretty much a provable NOP, it should not change
a single byte in the kernel image, as it replaces a macro use:

-#define cpu_has_arch_perfmon boot_cpu_has(X86_FEATURE_ARCH_PERFMON)

... with open-coded expressions of the same.

Thanks,

Ingo
Fengguang Wu
2016-05-25 00:54:03 UTC
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Hi Dave,

You are right -- this is a bad bisect.
[ 1.914984] random: trinity urandom read with 25 bits of entropy available
[ 8.542178] random: nonblocking pool is initialized
[ 11.939833] sock: process `trinity-main' is using obsolete setsockopt SO_BSDCOMPAT
[ 12.349890] BUG: unable to handle kernel paging request at 6b636170
[ 12.349895] IP: [<c108154b>] perf_prepare_sample+0x7d/0x263
The trace is more related to perf.
git bisect good 6b1291f3392c44c6e5a33e220615809ba7e09903 # 01:38 27+ 0 Merge 'ubifs/master' into devel-catchup-201605250104
git bisect good 3bd1789389525d3913f496b07937711164ce3809 # 01:51 27+ 0 Merge 'mark-rutland/arm64/misc-patches' into devel-catchup-201605250104
git bisect good 6944b78a365a8b71dabad7169896c3e75f253e8b # 01:56 27+ 0 Merge 'linux-review/Rajneesh-Bhardwaj/platform-x86-Add-PMC-Driver-for-Intel-Core-SoC/20160524-222735' into devel-catchup-201605250104
git bisect bad 5c7f53f3c9182146efd37be1989f8e23e3b796ff # 02:01 0- 1 Merge 'linux-review/Leon-Romanovsky/Netlink-based-IOCTLs-RDMA-ABI/20160524-223842' into devel-catchup-201605250104
git bisect bad be092017b6ffbd013f481f915632db6aa9fc3ca3 # 02:07 0- 1 Merge tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux
git bisect good 36db171cc733bc7b8c628ef21831467d1919decd # 02:14 27+ 0 Merge branch 'perf-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
git bisect bad 168f1a7163b37294a0ef33829e1ed54d41e33c42 # 02:19 1- 21 Merge branch 'x86-asm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
git bisect good 825a3b2605c3aa193e0075d0f9c72e33c17ab16a # 02:26 27+ 0 Merge branch 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
git bisect bad 93984fbd4e33cc861d5b49caed02a02cbfb01340 # 02:30 0- 2 x86/cpufeature: Replace cpu_has_apic with boot_cpu_has() usage
git bisect bad cb44d0cfc2969999a4d9e20e4fd8749fec6c5498 # 02:35 0- 12 Merge branch 'x86/cpu' into x86/asm, to merge more patches
git bisect bad d7847a7017b2a2759dd5590c0cffdbdf2994918e # 02:41 0- 1 x86/cpufeature: Fix build bug caused by merge artifact with the removal of cpu_has_hypervisor
git bisect bad 7b5e74e637e4a977c7cf40fd7de332f60b68180e # 03:36 0- 1 x86/cpufeature: Remove cpu_has_arch_perfmon
# first bad commit: [7b5e74e637e4a977c7cf40fd7de332f60b68180e] x86/cpufeature: Remove cpu_has_arch_perfmon
git bisect good 1e6d88ccf41c7ef2d6c99aa5e7fb9215aa0e5423 # 03:43 82+ 0 Merge tag 'nios2-v4.6-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/lftan/nios2
# extra tests with CONFIG_DEBUG_INFO_REDUCED
git bisect good 7b5e74e637e4a977c7cf40fd7de332f60b68180e # 03:50 82+ 0 x86/cpufeature: Remove cpu_has_arch_perfmon
# extra tests on HEAD of linux-devel/devel-catchup-201605250104
git bisect bad a43f260a02e7f31d72e082768ad0e32d97bdacbd # 03:50 0- 2 0day head guard for 'devel-catchup-201605250104'
# extra tests on tree/branch linus/master
git bisect bad 29567292c0b5b2fb484125c280a2175141fe2205 # 03:51 0- 63 Merge tag 'for-linus-4.7-rc0-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip
# extra tests on tree/branch linus/master
git bisect bad 29567292c0b5b2fb484125c280a2175141fe2205 # 03:51 0- 63 Merge tag 'for-linus-4.7-rc0-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip
# extra tests on tree/branch linux-next/master
Given the random nature of the test that triggered this, it seems more
plausible that this came from the perf-core-for-linus branch, and when
git-bisect ran on that branch, it marked it good because it didn't run
the fuzzer for long enough.
I just give 36db171cc733bc7b8c628ef21831467d1919decd ("Merge branch 'perf-core-for-linus' ...)
900 more runs and it looks good. So I'll queue more bisects.

Thanks,
Fengguang

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