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Subject[PATCH 3/4] perf lock contention: Avoid variable length arrays
Date
The msan also warns about the use of VLA for stack_trace variable.
We can dynamically allocate instead. While at it, simplify the error
handle a bit (and fix bugs).

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
tools/perf/util/bpf_lock_contention.c | 41 ++++++++++++++++++---------
1 file changed, 28 insertions(+), 13 deletions(-)

diff --git a/tools/perf/util/bpf_lock_contention.c b/tools/perf/util/bpf_lock_contention.c
index 06466da792e4..0deec1178778 100644
--- a/tools/perf/util/bpf_lock_contention.c
+++ b/tools/perf/util/bpf_lock_contention.c
@@ -108,28 +108,36 @@ int lock_contention_stop(void)

int lock_contention_read(struct lock_contention *con)
{
- int fd, stack;
+ int fd, stack, err = 0;
s32 prev_key, key;
struct lock_contention_data data = {};
- struct lock_stat *st;
+ struct lock_stat *st = NULL;
struct machine *machine = con->machine;
- u64 stack_trace[con->max_stack];
+ u64 *stack_trace;
+ size_t stack_size = con->max_stack * sizeof(*stack_trace);

fd = bpf_map__fd(skel->maps.lock_stat);
stack = bpf_map__fd(skel->maps.stacks);

con->lost = skel->bss->lost;

+ stack_trace = zalloc(stack_size);
+ if (stack_trace == NULL)
+ return -1;
+
prev_key = 0;
while (!bpf_map_get_next_key(fd, &prev_key, &key)) {
struct map *kmap;
struct symbol *sym;
int idx = 0;

+ /* to handle errors in the loop body */
+ err = -1;
+
bpf_map_lookup_elem(fd, &key, &data);
st = zalloc(sizeof(*st));
if (st == NULL)
- return -1;
+ break;

st->nr_contended = data.count;
st->wait_time_total = data.total_time;
@@ -163,25 +171,32 @@ int lock_contention_read(struct lock_contention *con)
st->name = strdup(sym->name);

if (ret < 0 || st->name == NULL)
- return -1;
+ break;
} else if (asprintf(&st->name, "%#lx", (unsigned long)st->addr) < 0) {
- free(st);
- return -1;
+ break;
}

if (verbose) {
- st->callstack = memdup(stack_trace, sizeof(stack_trace));
- if (st->callstack == NULL) {
- free(st);
- return -1;
- }
+ st->callstack = memdup(stack_trace, stack_size);
+ if (st->callstack == NULL)
+ break;
}

hlist_add_head(&st->hash_entry, con->result);
prev_key = key;
+
+ /* we're fine now, reset the values */
+ st = NULL;
+ err = 0;
}

- return 0;
+ free(stack_trace);
+ if (st) {
+ free(st->name);
+ free(st);
+ }
+
+ return err;
}

int lock_contention_finish(void)
--
2.38.1.273.g43a17bfeac-goog
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