From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Richter Subject: Re: [PATCH v3] perf test: Fix test trace+probe_vfs_getname.sh Date: Fri, 14 Feb 2020 14:54:11 +0100 Message-ID: <6d57be05-abaa-4ff5-1a07-6deb34fbb3d4@linux.ibm.com> References: <20200213122009.31810-1-tmricht@linux.ibm.com> <20200213143048.GA22170@kernel.org> <20200214020151.c93187535a8ccd0fb146a301@kernel.org> <20200213181140.GA28626@kernel.org> <20200214094550.228422235c7785519c7f24cc@kernel.org> <20200214130057.GB13462@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20200214130057.GB13462@kernel.org> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Arnaldo Carvalho de Melo Cc: Masami Hiramatsu , linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, gor@linux.ibm.com, sumanthk@linux.ibm.com, heiko.carstens@de.ibm.com List-Id: linux-perf-users.vger.kernel.org On 2/14/20 2:00 PM, Arnaldo Carvalho de Melo wrote: > Em Fri, Feb 14, 2020 at 10:44:06AM +0100, Thomas Richter escreveu: >> On 2/14/20 1:45 AM, Masami Hiramatsu wrote: >>> On Thu, 13 Feb 2020 15:11:40 -0300 >>> Arnaldo Carvalho de Melo wrote: >>> >>>> Em Fri, Feb 14, 2020 at 02:01:51AM +0900, Masami Hiramatsu escreveu: >>>>> On Thu, 13 Feb 2020 11:30:48 -0300 Arnaldo Carvalho de Melo wrote: >>>> >>>>>> Em Thu, Feb 13, 2020 at 01:20:09PM +0100, Thomas Richter escreveu: >>>>>>> This test places a kprobe to function getname_flags() in the kernel >>>>>>> which has the following prototype: >>>> >>>>>>> struct filename * >>>>>>> getname_flags(const char __user *filename, int flags, int *empty) >>>> >>>>>>> Variable filename points to a filename located in user space memory. >>>>>>> Looking at >>>>>>> commit 88903c464321c ("tracing/probe: Add ustring type for user-space string") >>>>>>> the kprobe should indicate that user space memory is accessed. >>>> >>>>>>> The following patch specifies user space memory access first and if this >>>>>>> fails use type 'string' in case 'ustring' is not supported. >>>> >>>>>> What are you fixing? >>>> >>>>>> I haven't seen any example of this test failing, and right now testing >>>>>> it with: >>>> >>>>>> [root@quaco ~]# uname -a >>>>>> Linux quaco 5.6.0-rc1+ #1 SMP Wed Feb 12 15:42:16 -03 2020 x86_64 x86_64 x86_64 GNU/Linux >>>>>> [root@quaco ~]# >>>> >>>>> This bug doesn't happen on x86 or other archs on which user-address space and >>>>> kernel address space is same. On some arch (ppc64 in this case?) user-address >>>>> space is partially or completely same as kernel address space. (Yes, they switch >>>>> the world when running into the kernel) In this case, we need to use different >>>>> data access functions for each spaces. That is why I introduced "ustring" type >>>>> for kprobe event. >>>>> As far as I can see, Thomas's patch is sane. >>>> >>>> Well, without his patch, on x86, the test he is claiming to be fixing >>>> works well, with his patch it stops working, see the rest of my reply. >>> >>> OK, let me see. >>> >>> >>>> diff --git a/tools/perf/tests/shell/lib/probe_vfs_getname.sh b/tools/perf/tests/shell/lib/probe_vfs_getname.sh >>>> index 7cb99b433888..30c1eadbc5be 100644 >>>> --- a/tools/perf/tests/shell/lib/probe_vfs_getname.sh >>>> +++ b/tools/perf/tests/shell/lib/probe_vfs_getname.sh >>>> @@ -13,7 +13,9 @@ add_probe_vfs_getname() { >>>> local verbose=$1 >>>> if [ $had_vfs_getname -eq 1 ] ; then >>>> line=$(perf probe -L getname_flags 2>&1 | egrep 'result.*=.*filename;' | sed -r 's/[[:space:]]+([[:digit:]]+)[[:space:]]+result->uptr.*/\1/') >>>> - perf probe -q "vfs_getname=getname_flags:${line} pathname=result->name:string" || \ >>>> + perf probe -q "vfs_getname=getname_flags:${line} pathname=result->uptr:ustring" || \ >>>> + perf probe $verbose "vfs_getname=getname_flags:${line} pathname=filename:ustring" || \ >>>> + perf probe -q "vfs_getname=getname_flags:${line} pathname=result->uptr:string" || \ >>>> perf probe $verbose "vfs_getname=getname_flags:${line} pathname=filename:string" >>>> fi >>>> } >>> >>> This looks no good (depends on architecture or debuginfo). In fs/namei.c, >>> >>> struct filename * >>> getname_flags(const char __user *filename, int flags, int *empty) >>> ... >>> kname = (char *)result->iname; >>> result->name = kname; >>> ... >>> result->uptr = filename; >>> result->aname = NULL; >>> audit_getname(result); >>> return result; >>> } >>> >>> And the line number script, egreps below line. >>> >>> result->uptr = filename; >>> >>> However, the probe on this line will hit *before* execute this line. >>> Note that kprobes is a breakpoint, which breaks into this line execution, >>> not after executed. >>> >>> So, I thik at this point, result->uptr should be NULL, but filename and >>> result->name already have assigned value. >>> >>> Thus, the fix should be something like below. >>> >>>> perf probe -q "vfs_getname=getname_flags:${line} pathname=result->name:string" || \ >>>> - perf probe $verbose "vfs_getname=getname_flags:${line} pathname=filename:string" >>>> + perf probe $verbose "vfs_getname=getname_flags:${line} pathname=filename:ustring" || \ >>> >>> Thomas, is this OK for you too, or would you have any reason to trace >>> result->uptr? >>> >>> Thank you, >>> >> >> Thank you very much for your help!!! >> >> I started from scratch and just installed linux 5.6.0rc1 without >> any changes and got this failure: >> >> [root@m35lp76 perf]# ./perf test 66 67 >> 66: Use vfs_getname probe to get syscall args filenames : FAILED! >> 67: Check open filename arg using perf trace + vfs_getname: FAILED! >> [root@m35lp76 perf]# >> >> Now I applied Masami's patch and this is the result >> >> [root@m35lp76 perf]# ./perf test 66 67 >> 66: Use vfs_getname probe to get syscall args filenames : Ok >> 67: Check open filename arg using perf trace + vfs_getname: Ok >> [root@m35lp76 perf >> >> Can we commit this patch? >> Thanks a lot > > So, I'll keep authorship to Thomas but will add a committer note stating > Masami's correction, is that ok? > > - Arnaldo > Sure go ahead. -- Thomas Richter, Dept 3252, IBM s390 Linux Development, Boeblingen, Germany -- Vorsitzender des Aufsichtsrats: Matthias Hartmann Geschäftsführung: Dirk Wittkopp Sitz der Gesellschaft: Böblingen / Registergericht: Amtsgericht Stuttgart, HRB 243294