Re: [x86/cpufeature] 7b5e74e637: BUG: unable to handle kernel paging request at 6b636170

2016-05-25 Thread Ingo Molnar 

* Dave Jones  wrote:

> On Wed, May 25, 2016 at 03:58:10AM +0800, kernel test robot wrote:
>  
>  > 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
>  > Author: Borislav Petkov 
>  > AuthorDate: Tue Mar 29 17:41:54 2016 +0200
>  > Commit: Ingo Molnar 
>  > 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: [] 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

Re: [x86/cpufeature] 7b5e74e637: BUG: unable to handle kernel paging request at 6b636170

2016-05-25 Thread Ingo Molnar 

* Dave Jones  wrote:

> On Wed, May 25, 2016 at 03:58:10AM +0800, kernel test robot wrote:
>  
>  > 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
>  > Author: Borislav Petkov 
>  > AuthorDate: Tue Mar 29 17:41:54 2016 +0200
>  > Commit: Ingo Molnar 
>  > 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: [] 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

Re: [x86/cpufeature] 7b5e74e637: BUG: unable to handle kernel paging request at 6b636170

2016-05-24 Thread Fengguang Wu 
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: [] 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 cb44d0cfc296a4d9e20e4fd8749fec6c5498  # 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

Re: [x86/cpufeature] 7b5e74e637: BUG: unable to handle kernel paging request at 6b636170

2016-05-24 Thread Fengguang Wu 
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: [] 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 cb44d0cfc296a4d9e20e4fd8749fec6c5498  # 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

Re: [x86/cpufeature] 7b5e74e637: BUG: unable to handle kernel paging request at 6b636170

2016-05-24 Thread Dave Jones 
On Wed, May 25, 2016 at 03:58:10AM +0800, kernel test robot wrote:
 
 > 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
 > Author: Borislav Petkov 
 > AuthorDate: Tue Mar 29 17:41:54 2016 +0200
 > Commit: Ingo Molnar 
 > 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: [] 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 cb44d0cfc296a4d9e20e4fd8749fec6c5498  # 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.

Dave

Re: [x86/cpufeature] 7b5e74e637: BUG: unable to handle kernel paging request at 6b636170

2016-05-24 Thread Dave Jones 
On Wed, May 25, 2016 at 03:58:10AM +0800, kernel test robot wrote:
 
 > 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
 > Author: Borislav Petkov 
 > AuthorDate: Tue Mar 29 17:41:54 2016 +0200
 > Commit: Ingo Molnar 
 > 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: [] 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 cb44d0cfc296a4d9e20e4fd8749fec6c5498  # 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.

Dave