Em Thu, Apr 21, 2016 at 12:17:07PM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Thu, Apr 21, 2016 at 12:48:58PM +0200, Peter Zijlstra escreveu:
> > On Wed, Apr 20, 2016 at 07:47:30PM -0300, Arnaldo Carvalho de Melo wrote:
> > > +++ b/kernel/events/callchain.c
>
> > > @@ -73,7 +81,7 @@ static int alloc_callchain_buffers(void)
> > > if (!entries)
> > > return -ENOMEM;
> > > - size = sizeof(struct perf_callchain_entry) * PERF_NR_CONTEXTS;
> > > + size = perf_callchain_entry__sizeof() * PERF_NR_CONTEXTS;
> > > for_each_possible_cpu(cpu) {
> > > entries->cpu_entries[cpu] = kmalloc_node(size, GFP_KERNEL,
> > And this alloc _will_ fail if you put in a decent sized value..
> > Should we put in a dmesg WARN if this alloc fails and
> > perf_event_max_stack is 'large' ?
>
> Unsure, it already returns -ENOMEM, see, some lines above, i.e. it
> better have error handling up this, ho-hum, call chain, I'm checking...
So, it is, using the tools, since it fits this bill:
[root@jouet acme]# perf probe get_callchain_buffers
Added new event:
probe:get_callchain_buffers (on get_callchain_buffers)
You can now use it in all perf tools, such as:
perf record -e probe:get_callchain_buffers -aR sleep 1
[root@jouet acme]# perf trace -e perf_event_open --event
probe:get_callchain_buffers/call-graph=fp/ -- perf record -g usleep 1
[ perf record: Woken up 1 times to write data ]
26.740 ( 0.008 ms): perf/1264 perf_event_open(attr_uptr: 0x1e6b618, pid:
1265, group_fd: -1, flags: FD_CLOEXEC) ...
26.740 ( ): probe:get_callchain_buffers:(ffffffff811a9480))
get_callchain_buffers+0xfe200001
([kernel.kallsyms])
SYSC_perf_event_open+0xfe2003bc
([kernel.kallsyms])
sys_perf_event_open+0xfe200009
([kernel.kallsyms])
do_syscall_64+0xfe200062
([kernel.kallsyms])
return_from_SYSCALL_64+0xfe200000
([kernel.kallsyms])
syscall+0xffff0179d3c22019
(/usr/lib64/libc-2.22.so)
cmd_record+0xffffffffff8005fc
(/home/acme/bin/perf)
run_builtin+0xffffffffff800061
(/home/acme/bin/perf)
main+0xffffffffff800672
(/home/acme/bin/perf)
__libc_start_main+0xffff0179d3c220f0
(/usr/lib64/libc-2.22.so)
26.749 ( 0.016 ms): perf/1264 ... [continued]: perf_event_open()) = 4
<SNIP the perf_event_open syscalls for the other 3 CPUs in this system)
So, if we put some too big value there and the allocation fails, people asking
for callchains will get that -ENOMEM back in their face.
I'll do this test, i.e. put some huge value there and ask for callchains...
- Arnaldo
