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 10:04:30 -0300 Message-ID: <20200214130430.GC13462@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: <20200214094550.228422235c7785519c7f24cc@kernel.org> Sender: linux-kernel-owner@vger.kernel.org To: Masami Hiramatsu Cc: Thomas Richter , 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 09:45:50AM +0900, Masami Hiramatsu escreveu: > 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? Ok, I retract my last e-mail, can you provide a final patch with the fix? - Arnaldo