On Fri, Apr 22, 2016 at 04:05:31PM -0600, David Ahern wrote: > On 4/22/16 2:52 PM, Arnaldo Carvalho de Melo wrote: > >Em Wed, Apr 20, 2016 at 04:04:12PM -0700, Alexei Starovoitov escreveu: > >>On Wed, Apr 20, 2016 at 07:47:30PM -0300, Arnaldo Carvalho de Melo wrote: > > > >>Nice. I like it. That's a great approach to hard problem. > >>Java guys will be happy too. > >>Please also adjust two places in kernel/bpf/stackmap.c > > > >>>+ { > >>>+ .procname = "perf_event_max_stack", > >>>+ .data = NULL, /* filled in by handler */ > >>>+ .maxlen = sizeof(sysctl_perf_event_max_stack), > >>>+ .mode = 0644, > >>>+ .proc_handler = perf_event_max_stack_handler, > >>>+ .extra1 = &zero, > > > >>zero seems to be the wrong minimum. I think it should be at least 2 to > >>to fit user/kernel tags ? Probably needs to define max as well. > > > >So, if someone asks for zero, it will not copy anything, but then, this > >would be what the user had asked for :-) > > > >Ditto for the max, if someone asks for too big a callchain, then when > >allocating it it will fail and no callchain will be produced, that or it > >will be able to allocate but will take too long copying that many > >addresses, and we would be prevented from doing so by some other > >protection, iirc there is perf_cpu_time_max_percent, and then buffer > >space will run out. > > > >So I think that leaving it as is is enough, no? > > > >Can I keep your Acked-by? David, can I keep yours? > > Yes > > > >diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c > >index 343c22f5e867..6fe77349fa9d 100644 > >--- a/kernel/events/callchain.c > >+++ b/kernel/events/callchain.c > >@@ -18,6 +18,14 @@ struct callchain_cpus_entries { > > struct perf_callchain_entry *cpu_entries[0]; > > }; > > > >+int sysctl_perf_event_max_stack __read_mostly = PERF_MAX_STACK_DEPTH; > >+ > >+static size_t perf_callchain_entry__sizeof(void) > >+{ > >+ return sizeof(struct perf_callchain_entry) + > >+ sizeof(__u64) * sysctl_perf_event_max_stack; > >+} > >+ > > To Alexei's comment, a max_stack of 0 still has a non-zero alloc size so > that should be ok. > > > > static DEFINE_PER_CPU(int, callchain_recursion[PERF_NR_CONTEXTS]); > > static atomic_t nr_callchain_events; > > static DEFINE_MUTEX(callchain_mutex); > >@@ -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,
right... and looking into it further, realized that the patch is broken, since get_callchain_entry() is doing: return &entries->cpu_entries[cpu][*rctx]; whereas it should be dynamic offset based on sysctl_perf_event_max_stack*8 So definitely needs another respin.