From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnaldo Carvalho de Melo Subject: Re: [PATCH v3] perf test: Fix test trace+probe_vfs_getname.sh Date: Fri, 14 Feb 2020 10:00:57 -0300 Message-ID: <20200214130057.GB13462@kernel.org> References: <20200213122009.31810-1-tmricht@linux.ibm.com> <20200213143048.GA22170@kernel.org> <20200214020151.c93187535a8ccd0fb146a301@kernel.org> <20200213181140.GA28626@kernel.org> <20200214094550.228422235c7785519c7f24cc@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Thomas Richter 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 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