Messages in this thread | | | Date | Tue, 22 Feb 2011 09:10:46 -0300 | From | Arnaldo Carvalho de Melo <> | Subject | Re: [PATCH 1/2] perf probe: Fix error propagation leading to segfault |
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Em Tue, Feb 22, 2011 at 12:20:22PM +0900, Masami Hiramatsu escreveu: > (2011/02/22 10:31), Arnaldo Carvalho de Melo wrote: > > From: Arnaldo Carvalho de Melo <acme@redhat.com> > > There are two hunks in this patch that stops probe processing as soon as one > > error is found, breaking out of loops, the other fix an error propagation that > > should return a negative error number but instead was returning the result of > > "ret < 0", which is 1 and thus made several error checks fail because they test > > agains < 0. > > > > The problem could be triggered by asking for a variable that was optimized out, > > fact that should stop the whole probe processing but instead was segfaulting > > while installing broken probes: > > > > [root@emilia ~]# probe perf_mmap:55 user_lock_limit > > Failed to find the location of user_lock_limit at this address. > > Perhaps, it has been optimized out. > > Failed to find 'user_lock_limit' in this function. > > Add new events: > > probe:perf_mmap (on perf_mmap:55 with user_lock_limit) > > probe:perf_mmap_1 (on perf_mmap:55 with user_lock_limit) > > Segmentation fault (core dumped) > > [root@emilia ~]# perf probe -l > > probe:perf_mmap (on perf_mmap:55@git/linux/kernel/perf_event.c with user_lock_limit) > > probe:perf_mmap_1 (on perf_mmap:55@git/linux/kernel/perf_event.c with user_lock_limit) > > [root@emilia ~]# > > > > After the fix: > > > > [root@emilia ~]# probe perf_mmap:55 user_lock_limit > > Failed to find the location of user_lock_limit at this address. > > Perhaps, it has been optimized out. > > Failed to find 'user_lock_limit' in this function. > > Error: Failed to add events. (-2) > > [root@emilia ~]# > > Oops, thanks! But I've also found this fix including some > redundant checks.
I'll remove the redundancies as I describe later on this message.
> > Cc: Frederic Weisbecker <fweisbec@gmail.com> > > Cc: Ingo Molnar <mingo@elte.hu> > > Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> > > Cc: Mike Galbraith <efault@gmx.de> > > Cc: Paul Mackerras <paulus@samba.org> > > Cc: Peter Zijlstra <peterz@infradead.org> > > Cc: Stephane Eranian <eranian@google.com> > > Cc: Tom Zanussi <tzanussi@gmail.com> > > LKML-Reference: <new-submission> > > Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com> > > --- > > tools/perf/util/probe-event.c | 5 ++++- > > tools/perf/util/probe-finder.c | 4 +++- > > 2 files changed, 7 insertions(+), 2 deletions(-) > > > > diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c > > index 0e3ea13..369ddc6 100644 > > --- a/tools/perf/util/probe-event.c > > +++ b/tools/perf/util/probe-event.c > > @@ -1832,9 +1832,12 @@ int add_perf_probe_events(struct perf_probe_event *pevs, int npevs, > > } > > > > /* Loop 2: add all events */ > > - for (i = 0; i < npevs && ret >= 0; i++) > > + for (i = 0; i < npevs && ret >= 0; i++) { > > ret = __add_probe_trace_events(pkgs[i].pev, pkgs[i].tevs, > > pkgs[i].ntevs, force_add); > > + if (ret < 0) > > + break; > > + } > > Hmm, we've already checked ret >= 0 in for().
You see? There is value in sticking to common practices, even being one line above I automatically looked after the assignment, not before. :-\
For that to work one needs to make sure to have ret initialized to zero before the loop and do an unneeded test before we start the __add_probe_trace_events calls.
> > end: > > /* Loop 3: cleanup and free trace events */ > > for (i = 0; i < npevs; i++) { > > diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c > > index fe461f6..eecbdca 100644 > > --- a/tools/perf/util/probe-finder.c > > +++ b/tools/perf/util/probe-finder.c > > @@ -1262,7 +1262,7 @@ static int probe_point_line_walker(const char *fname, int lineno, > > ret = call_probe_finder(NULL, pf); > > > > /* Continue if no error, because the line will be in inline function */ > > - return ret < 0 ?: 0; > > + return ret < 0 ? ret : 0; > > I think the problem is only here. > > > } > > > > /* Find probe point from its line number */ > > @@ -1484,6 +1484,8 @@ static int find_probes(int fd, struct probe_finder *pf) > > pf->lno = pp->line; > > ret = find_probe_point_by_line(pf); > > } > > + if (ret != DWARF_CB_OK) > > + break; > > Actually, we must check that ret < 0 here, and that has been checked > in while().
Ok, another instance of the above pet peeve of mine :-)
> > } > > off = noff; > > } > > Only with the second hunk of the patch, I've checked that is enough to fix > the problem. > > $ ./perf probe -vv perf_mmap:55 user_lock_limit > probe-definition(0): perf_mmap:55 user_lock_limit > symbol:perf_mmap file:(null) line:55 offset:0 return:0 lazy:(null) > parsing arg: user_lock_limit into user_lock_limit > 1 arguments > Looking at the vmlinux_path (6 entries long) > Using //lib/modules/2.6.38-rc5-tip+/build/vmlinux for symbols > Try to open /lib/modules/2.6.38-rc5-tip+/build/vmlinux > Get 4514 lines from this CU > Probe point found: perf_mmap+352 > Searching 'user_lock_limit' variable in context. > Converting variable user_lock_limit into trace event. > user_lock_limit type is long unsigned int. > Probe point found: perf_mmap+359 > Searching 'user_lock_limit' variable in context. > Converting variable user_lock_limit into trace event. > user_lock_limit type is long unsigned int. > Probe point found: perf_mmap+322 > Searching 'user_lock_limit' variable in context. > Converting variable user_lock_limit into trace event. > Failed to find the location of user_lock_limit at this address. > Perhaps, it has been optimized out. > Failed to find 'user_lock_limit' in this function. > An error occurred in debuginfo analysis (-2). > Error: Failed to add events. (-2)
Thanks for checking,
- Arnaldo
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