Re: [PATCH] perf header: Fix lock/unlock imbalances

[Arnaldo Carvalho de Melo]

Em Mon, Apr 08, 2019 at 01:26:09PM -0500, Gustavo A. R. Silva escreveu:
> 
> 
> On 4/8/19 1:22 PM, Song Liu wrote:
> > 
> > 
> >> On Apr 8, 2019, at 10:33 AM, Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx> wrote:
> >>
> >> Fix lock/unlock imbalances by refactoring the code a bit and adding
> >> calls to up_write() before return.
> >>
> >> Addresses-Coverity-ID: 1444315 ("Missing unlock")
> >> Addresses-Coverity-ID: 1444316 ("Missing unlock")
> >> Fixes: a70a1123174a ("perf bpf: Save BTF information as headers to perf.data")
> >> Fixes: 606f972b1361 ("perf bpf: Save bpf_prog_info information as headers to perf.data")
> >> Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
> > 
> > Acked-by: Song Liu <songliubraving@xxxxxx>
> > 
> > Thanks for the fix!
> > 
> 
> Glad to help. :)

Super cool, using the same idiom as the kernel and living in the kernel
sources has its advantages 8-)

But see below, 

> >> +++ b/tools/perf/util/header.c
> >> @@ -2606,6 +2606,7 @@ static int process_bpf_prog_info(struct feat_fd *ff, void *data __maybe_unused)
> >> 		perf_env__insert_bpf_prog_info(env, info_node);
> >> 	}
> >>
> >> +	up_write(&env->bpf_progs.lock);
> >> 	return 0;
> >> out:
> >> 	free(info_linear);
> >> @@ -2623,7 +2624,9 @@ static int process_bpf_prog_info(struct feat_fd *ff __maybe_unused, void *data _
> >> static int process_bpf_btf(struct feat_fd *ff, void *data __maybe_unused)
> >> {
> >> 	struct perf_env *env = &ff->ph->env;
> >> +	struct btf_node *node;
> >> 	u32 count, i;
> >> +	int err = -1;

Why are you using this 'err' variable? It is only set here and at the
end, i.e. one write, one read. We could as well have that out: block
return -1 straight away.

Else we could do, see below

> >>
> >> 	if (ff->ph->needs_swap) {
> >> 		pr_warning("interpreting btf from systems with endianity is not yet supported\n");
> >> @@ -2636,31 +2639,33 @@ static int process_bpf_btf(struct feat_fd *ff, void *data __maybe_unused)
> >> 	down_write(&env->bpf_progs.lock);
> >>
> >> 	for (i = 0; i < count; ++i) {
> >> -		struct btf_node *node;
> >> 		u32 id, data_size;
> >>
> >> +		node = NULL;
> >> 		if (do_read_u32(ff, &id))
> >> -			return -1;
> >> +			goto out;
> >> 		if (do_read_u32(ff, &data_size))
> >> -			return -1;
> >> +			goto out;
> >>
> >> 		node = malloc(sizeof(struct btf_node) + data_size);
> >> 		if (!node)
> >> -			return -1;
> >> +			goto out;
> >>
> >> 		node->id = id;
> >> 		node->data_size = data_size;
> >>
> >> -		if (__do_read(ff, node->data, data_size)) {
> >> -			free(node);
> >> -			return -1;
> >> -		}
> >> +		if (__do_read(ff, node->data, data_size))
> >> +			goto out;
> >>
> >> 		perf_env__insert_btf(env, node);
> >> 	}

      err = 0;

> >>

out:

> >> 	up_write(&env->bpf_progs.lock);

      return err;

And delete the rest.

but I see, you used the same pattern in the first #ifdef HAVE_LIBBPF_SUPPORT
block :-)

Anyway, since we're fixing up that other case, we might as well
streamline this, please check the patch below.

> >> 	return 0;

> >> +out:
> >> +	up_write(&env->bpf_progs.lock);
> >> +	free(node);
> >> +	return err;

So, that is what I'm applying, please holler if I introduced some
problem:

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index b9e693825873..2d2af2ac2b1e 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -2606,6 +2606,7 @@ static int process_bpf_prog_info(struct feat_fd *ff, void *data __maybe_unused)
 		perf_env__insert_bpf_prog_info(env, info_node);
 	}
 
+	up_write(&env->bpf_progs.lock);
 	return 0;
 out:
 	free(info_linear);
@@ -2623,7 +2624,9 @@ static int process_bpf_prog_info(struct feat_fd *ff __maybe_unused, void *data _
 static int process_bpf_btf(struct feat_fd *ff, void *data __maybe_unused)
 {
 	struct perf_env *env = &ff->ph->env;
+	struct btf_node *node = NULL;
 	u32 count, i;
+	int err = -1;
 
 	if (ff->ph->needs_swap) {
 		pr_warning("interpreting btf from systems with endianity is not yet supported\n");
@@ -2636,31 +2639,32 @@ static int process_bpf_btf(struct feat_fd *ff, void *data __maybe_unused)
 	down_write(&env->bpf_progs.lock);
 
 	for (i = 0; i < count; ++i) {
-		struct btf_node *node;
 		u32 id, data_size;
 
 		if (do_read_u32(ff, &id))
-			return -1;
+			goto out;
 		if (do_read_u32(ff, &data_size))
-			return -1;
+			goto out;
 
 		node = malloc(sizeof(struct btf_node) + data_size);
 		if (!node)
-			return -1;
+			goto out;
 
 		node->id = id;
 		node->data_size = data_size;
 
-		if (__do_read(ff, node->data, data_size)) {
-			free(node);
-			return -1;
-		}
+		if (__do_read(ff, node->data, data_size))
+			goto out;
 
 		perf_env__insert_btf(env, node);
+		node = NULL;
 	}
 
+	err = 0;
+out:
 	up_write(&env->bpf_progs.lock);
-	return 0;
+	free(node);
+	return err;
 }
 
 struct feature_ops {