perf symbol: Add blocking argument to filename__read_build_id

When synthesizing build-ids, for build ID mmap2 events, they will be
added for data mmaps if -d/--data is specified. The files opened for
their build IDs may block on the open causing perf to hang during
synthesis. There is some robustness in existing calls to
filename__read_build_id by checking the file path is to a regular
file, which unfortunately fails for symlinks. Rather than adding more
is_regular_file calls, switch filename__read_build_id to take a
"block" argument and specify O_NONBLOCK when this is false. The
existing is_regular_file checking callers and the event synthesis
callers are made to pass false and thereby avoiding the hang.

Fixes: 53b00ff358dc ("perf record: Make --buildid-mmap the default")
Signed-off-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20250823000024.724394-3-irogers@google.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

8 files changed, 24 insertions, 19 deletions

diff --git a/tools/perf/util/build-id.c b/tools/perf/util/build-id.c
index a7018a3b0437..bf7f3268b9a2 100644
--- a/tools/perf/util/build-id.c
+++ b/tools/perf/util/build-id.c
@@ -115,7 +115,7 @@ int filename__snprintf_build_id(const char *pathname, char *sbuild_id, size_t sb
 	struct build_id bid = { .size = 0, };
 	int ret;
 
-	ret = filename__read_build_id(pathname, &bid);
+	ret = filename__read_build_id(pathname, &bid, /*block=*/true);
 	if (ret < 0)
 		return ret;
 
@@ -841,7 +841,7 @@ static int filename__read_build_id_ns(const char *filename,
 	int ret;
 
 	nsinfo__mountns_enter(nsi, &nsc);
-	ret = filename__read_build_id(filename, bid);
+	ret = filename__read_build_id(filename, bid, /*block=*/true);
 	nsinfo__mountns_exit(&nsc);
 
 	return ret;
diff --git a/tools/perf/util/debuginfo.c b/tools/perf/util/debuginfo.c
index a44c70f93156..bb9ebd84ec2d 100644
--- a/tools/perf/util/debuginfo.c
+++ b/tools/perf/util/debuginfo.c
@@ -110,8 +110,12 @@ struct debuginfo *debuginfo__new(const char *path)
 	if (!dso)
 		goto out;
 
-	/* Set the build id for DSO_BINARY_TYPE__BUILDID_DEBUGINFO */
-	if (is_regular_file(path) && filename__read_build_id(path, &bid) > 0)
+	/*
+	 * Set the build id for DSO_BINARY_TYPE__BUILDID_DEBUGINFO. Don't block
+	 * incase the path isn't for a regular file.
+	 */
+	assert(!dso__has_build_id(dso));
+	if (filename__read_build_id(path, &bid, /*block=*/false) > 0)
 		dso__set_build_id(dso, &bid);
 
 	for (type = distro_dwarf_types;
diff --git a/tools/perf/util/dsos.c b/tools/perf/util/dsos.c
index 0a7645c7fae7..64c1d65b0149 100644
--- a/tools/perf/util/dsos.c
+++ b/tools/perf/util/dsos.c
@@ -81,13 +81,13 @@ static int dsos__read_build_ids_cb(struct dso *dso, void *data)
 		return 0;
 	}
 	nsinfo__mountns_enter(dso__nsinfo(dso), &nsc);
-	if (filename__read_build_id(dso__long_name(dso), &bid) > 0) {
+	if (filename__read_build_id(dso__long_name(dso), &bid, /*block=*/true) > 0) {
 		dso__set_build_id(dso, &bid);
 		args->have_build_id = true;
 	} else if (errno == ENOENT && dso__nsinfo(dso)) {
 		char *new_name = dso__filename_with_chroot(dso, dso__long_name(dso));
 
-		if (new_name && filename__read_build_id(new_name, &bid) > 0) {
+		if (new_name && filename__read_build_id(new_name, &bid, /*block=*/true) > 0) {
 			dso__set_build_id(dso, &bid);
 			args->have_build_id = true;
 		}
diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 6d2c280a1730..033c79231a54 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -902,7 +902,7 @@ out_close:
 
 #else // HAVE_LIBBFD_BUILDID_SUPPORT
 
-static int read_build_id(const char *filename, struct build_id *bid)
+static int read_build_id(const char *filename, struct build_id *bid, bool block)
 {
 	size_t size = sizeof(bid->data);
 	int fd, err = -1;
@@ -911,7 +911,7 @@ static int read_build_id(const char *filename, struct build_id *bid)
 	if (size < BUILD_ID_SIZE)
 		goto out;
 
-	fd = open(filename, O_RDONLY);
+	fd = open(filename, block ? O_RDONLY : (O_RDONLY | O_NONBLOCK));
 	if (fd < 0)
 		goto out;
 
@@ -934,7 +934,7 @@ out:
 
 #endif // HAVE_LIBBFD_BUILDID_SUPPORT
 
-int filename__read_build_id(const char *filename, struct build_id *bid)
+int filename__read_build_id(const char *filename, struct build_id *bid, bool block)
 {
 	struct kmod_path m = { .name = NULL, };
 	char path[PATH_MAX];
@@ -958,9 +958,10 @@ int filename__read_build_id(const char *filename, struct build_id *bid)
 		}
 		close(fd);
 		filename = path;
+		block = true;
 	}
 
-	err = read_build_id(filename, bid);
+	err = read_build_id(filename, bid, block);
 
 	if (m.comp)
 		unlink(filename);
diff --git a/tools/perf/util/symbol-minimal.c b/tools/perf/util/symbol-minimal.c
index 8d41bd7842df..41e4ebe5eac5 100644
--- a/tools/perf/util/symbol-minimal.c
+++ b/tools/perf/util/symbol-minimal.c
@@ -85,7 +85,7 @@ int filename__read_debuglink(const char *filename __maybe_unused,
 /*
  * Just try PT_NOTE header otherwise fails
  */
-int filename__read_build_id(const char *filename, struct build_id *bid)
+int filename__read_build_id(const char *filename, struct build_id *bid, bool block)
 {
 	int fd, ret = -1;
 	bool need_swap = false, elf32;
@@ -102,7 +102,7 @@ int filename__read_build_id(const char *filename, struct build_id *bid)
 	void *phdr, *buf = NULL;
 	ssize_t phdr_size, ehdr_size, buf_size = 0;
 
-	fd = open(filename, O_RDONLY);
+	fd = open(filename, block ? O_RDONLY : (O_RDONLY | O_NONBLOCK));
 	if (fd < 0)
 		return -1;
 
@@ -323,7 +323,7 @@ int dso__load_sym(struct dso *dso, struct map *map __maybe_unused,
 	if (ret >= 0)
 		RC_CHK_ACCESS(dso)->is_64_bit = ret;
 
-	if (filename__read_build_id(ss->name, &bid) > 0)
+	if (filename__read_build_id(ss->name, &bid, /*block=*/true) > 0)
 		dso__set_build_id(dso, &bid);
 	return 0;
 }
diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index e816e4220d33..3fed54de5401 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -1869,14 +1869,14 @@ int dso__load(struct dso *dso, struct map *map)
 
 	/*
 	 * Read the build id if possible. This is required for
-	 * DSO_BINARY_TYPE__BUILDID_DEBUGINFO to work
+	 * DSO_BINARY_TYPE__BUILDID_DEBUGINFO to work. Don't block in case path
+	 * isn't for a regular file.
 	 */
-	if (!dso__has_build_id(dso) &&
-	    is_regular_file(dso__long_name(dso))) {
+	if (!dso__has_build_id(dso)) {
 		struct build_id bid = { .size = 0, };
 
 		__symbol__join_symfs(name, PATH_MAX, dso__long_name(dso));
-		if (filename__read_build_id(name, &bid) > 0)
+		if (filename__read_build_id(name, &bid, /*block=*/false) > 0)
 			dso__set_build_id(dso, &bid);
 	}
 
diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
index 3fb5d146d9b1..347106218799 100644
--- a/tools/perf/util/symbol.h
+++ b/tools/perf/util/symbol.h
@@ -140,7 +140,7 @@ struct symbol *dso__next_symbol(struct symbol *sym);
 
 enum dso_type dso__type_fd(int fd);
 
-int filename__read_build_id(const char *filename, struct build_id *id);
+int filename__read_build_id(const char *filename, struct build_id *id, bool block);
 int sysfs__read_build_id(const char *filename, struct build_id *bid);
 int modules__parse(const char *filename, void *arg,
 		   int (*process_module)(void *arg, const char *name,
diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
index cb2c1ace304a..fcd1fd13c30e 100644
--- a/tools/perf/util/synthetic-events.c
+++ b/tools/perf/util/synthetic-events.c
@@ -401,7 +401,7 @@ static void perf_record_mmap2__read_build_id(struct perf_record_mmap2 *event,
 	nsi = nsinfo__new(event->pid);
 	nsinfo__mountns_enter(nsi, &nc);
 
-	rc = filename__read_build_id(event->filename, &bid) > 0 ? 0 : -1;
+	rc = filename__read_build_id(event->filename, &bid, /*block=*/false) > 0 ? 0 : -1;
 
 	nsinfo__mountns_exit(&nc);
 	nsinfo__put(nsi);