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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Thu, 30 May 2019 11:27:41 +0100 Received: from d06av22.portsmouth.uk.ibm.com (d06av22.portsmouth.uk.ibm.com [9.149.105.58]) by b06cxnps4076.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x4UAReQt47120454 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 30 May 2019 10:27:40 GMT Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 794BC4C046; Thu, 30 May 2019 10:27:40 +0000 (GMT) Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9ABA84C040; Thu, 30 May 2019 10:27:37 +0000 (GMT) Received: from [9.124.31.34] (unknown [9.124.31.34]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTP; Thu, 30 May 2019 10:27:37 +0000 (GMT) Subject: Re: [PATCH] perf: Fix oops when kthread execs user process To: Peter Zijlstra References: <1559046689-24091-1-git-send-email-92siuyang@gmail.com> <20190528140103.GT2623@hirez.programming.kicks-ass.net> <20190528153224.GE20758@fuggles.cambridge.arm.com> <20190528173228.GW2623@hirez.programming.kicks-ass.net> <20190529091733.GA4485@fuggles.cambridge.arm.com> <20190529101042.GN2623@hirez.programming.kicks-ass.net> <20190529102022.GC4485@fuggles.cambridge.arm.com> <20190529125557.GU2623@hirez.programming.kicks-ass.net> From: Ravi Bangoria Date: Thu, 30 May 2019 15:57:36 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-TM-AS-GCONF: 00 x-cbid: 19053010-0020-0000-0000-00000341EE47 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19053010-0021-0000-0000-00002194F31E Message-Id: <8b55f79a-c324-0701-e85f-c7797a60a708@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:, , definitions=2019-05-30_06:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1905300079 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190530_032751_272240_107012EF X-CRM114-Status: GOOD ( 24.10 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mark.rutland@arm.com, Ravi Bangoria , Young Xiao <92siuyang@gmail.com>, mpe@ellerman.id.au, jolsa@redhat.com, x86@kernel.org, Will Deacon , linux@armlinux.org.uk, eranian@google.com, linux-kernel@vger.kernel.org, acme@redhat.com, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, ravi.bangoria@linux.vnet.ibm.com, fweisbec@gmail.com, linux-arm-kernel@lists.infradead.org, kan.liang@linux.intel.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 5/30/19 2:08 PM, Ravi Bangoria wrote: >> --- >> Subject: perf: Fix perf_sample_regs_user() >> From: Peter Zijlstra >> Date: Wed May 29 14:37:24 CEST 2019 >> >> perf_sample_regs_user() uses 'current->mm' to test for the presence of >> userspace, but this is insufficient, consider use_mm(). >> >> A better test is: '!(current->flags & PF_KTHREAD)', exec() clears >> PF_KTHREAD after it sets the new ->mm but before it drops to userspace >> for the first time. > > This looks correct. I'll give it a try. > >> >> Possibly obsoletes: bf05fc25f268 ("powerpc/perf: Fix oops when kthread execs user process") >> >> Reported-by: Ravi Bangoria >> Reported-by: Young Xiao <92siuyang@gmail.com> >> Cc: Ravi Bangoria >> Cc: Naveen N. Rao >> Cc: Michael Ellerman >> Cc: Jiri Olsa >> Cc: Frederic Weisbecker >> Cc: Stephane Eranian >> Cc: Arnaldo Carvalho de Melo >> Acked-by: Will Deacon >> Fixes: 4018994f3d87 ("perf: Add ability to attach user level registers dump to sample") >> Signed-off-by: Peter Zijlstra (Intel) >> --- >> kernel/events/core.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> --- a/kernel/events/core.c >> +++ b/kernel/events/core.c >> @@ -5923,7 +5923,7 @@ static void perf_sample_regs_user(struct >> if (user_mode(regs)) { >> regs_user->abi = perf_reg_abi(current); >> regs_user->regs = regs; >> - } else if (current->mm) { >> + } else if (!(current->flags & PF_KTHREAD)) { With this patch applied and my patch reverted, I still see it crashing because current->flags does not have PF_KTHREAD set. Sample trace with v5.0 kernel: BUG: Kernel NULL pointer dereference at 0x00000000 Faulting instruction address: 0xc0000000000f1a6c Oops: Kernel access of bad area, sig: 11 [#1] LE SMP NR_CPUS=2048 NUMA pSeries CPU: 17 PID: 3241 Comm: systemd-cgroups Kdump: loaded Not tainted 5.0.0+ #7 NIP: c0000000000f1a6c LR: c0000000002acc7c CTR: c0000000002a8f90 REGS: c0000001e80469a0 TRAP: 0300 Not tainted (5.0.0+) MSR: 8000000000001033 CR: 48022448 XER: 20000000 CFAR: c00000000000deb4 DAR: 0000000000000000 DSISR: 40000000 IRQMASK: 1 GPR00: c0000000002acc7c c0000001e8046c30 c000000001607500 0000000000000000 GPR04: 0000000000000000 0000000000000000 0000000000000000 c000000000128618 GPR08: 000007ffffffffff 0000000000000000 ffffffffffffffff c00000000001cd40 GPR12: c000000000446fd8 c00000003ffdf080 00000000ffff0000 0000000000000007 GPR16: c0000001edd74988 c0000001edd60400 00007fff89801130 000000000005e1b0 GPR20: c0000001edb77a08 c0000001e8047208 c0000001f03d9800 c0000001e8046e00 GPR24: 000000000000b1af c000000001126938 c0000001f03d9b28 0000000000010000 GPR28: c0000001e8046d30 0000000000000000 0000000000000000 0000000000000000 NIP [c0000000000f1a6c] perf_reg_value+0x5c/0xc0 LR [c0000000002acc7c] perf_output_sample_regs+0x6c/0xd0 Call Trace: [c0000001e8046c30] [c0000000002acc7c] perf_output_sample_regs+0x6c/0xd0 (unreliable) [c0000001e8046c80] [c0000000002b9cd0] perf_output_sample+0x620/0x8c0 [c0000001e8046d10] [c0000000002ba6b4] perf_event_output_forward+0x64/0x90 [c0000001e8046d80] [c0000000002b2908] __perf_event_overflow+0x88/0x1e0 [c0000001e8046dd0] [c0000000000f3d18] record_and_restart+0x288/0x670 [c0000001e8047180] [c0000000000f4c18] perf_event_interrupt+0x2b8/0x4b0 [c0000001e8047280] [c00000000002b380] performance_monitor_exception+0x50/0x70 [c0000001e80472a0] [c000000000009ca0] performance_monitor_common+0x110/0x120 --- interrupt: f01 at slice_scan_available+0x20/0xc0 LR = slice_find_area+0x174/0x210 [c0000001e8047630] [c000000000083ea0] slice_get_unmapped_area+0x3d0/0x7f0 [c0000001e8047ae0] [c00000000032d5b0] get_unmapped_area+0xa0/0x170 [c0000001e8047b10] [c00000000001cd40] arch_setup_additional_pages+0xc0/0x1c0 [c0000001e8047b60] [c000000000446fd8] load_elf_binary+0xb48/0x1580 [c0000001e8047c80] [c0000000003c3938] search_binary_handler+0xe8/0x2a0 [c0000001e8047d10] [c0000000003c42f4] __do_execve_file.isra.13+0x694/0x980 [c0000001e8047de0] [c000000000128618] call_usermodehelper_exec_async+0x248/0x290 [c0000001e8047e20] [c00000000000b65c] ret_from_kernel_thread+0x5c/0x80 Instruction dump: 7c9e2378 7c7f1b78 f8010010 f821ffd1 419e0044 3d22ff6b 7bc41764 3929ae10 7d29202e 2b890150 419d003c 38210030 <7c7f482a> e8010010 ebc1fff0 ebe1fff8 ---[ end trace 54f3492ad1d403d8 ]--- _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel