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

[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 <bp@xxxxxxx>
 > AuthorDate: Tue Mar 29 17:41:54 2016 +0200
 > Commit:     Ingo Molnar <mingo@xxxxxxxxxx>
 > 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.
 
 > 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.

	Dave