[PATCH 3/5] perf dso: Use stored fd error instead of stale errno in file_read()

[Arnaldo Carvalho de Melo]

From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>

file_read() uses ret = -errno when dso__data(dso)->fd is negative after
try_to_open_dso() fails.  By this point errno has been through
mutex_lock(), nsinfo__mountns_enter(), and multiple open() attempts
inside try_to_open_dso() — it no longer reflects the actual open
failure.  If errno happens to be 0, ret = 0 looks like EOF rather than
an error.

The fd field already carries the negated errno from __open_dso()
(e.g. -EINVAL, -ENOENT), so use it directly instead of reading the
stale global errno.

Fixes: 33bdedcea2d7 ("perf tools: Protect dso cache fd with a mutex")
Reported-by: sashiko-bot <sashiko-bot@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Assisted-by: Claude:claude-opus-4.6
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/dso.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
index 124193453675ca18..845a384a4d56779b 100644
--- a/tools/perf/util/dso.c
+++ b/tools/perf/util/dso.c
@@ -1029,7 +1029,8 @@ static ssize_t file_read(struct dso *dso, struct machine *machine,
 
 	if (dso__data(dso)->fd < 0) {
 		dso__data(dso)->status = DSO_DATA_STATUS_ERROR;
-		ret = -errno;
+		/* fd already carries the negated errno from __open_dso() */
+		ret = dso__data(dso)->fd;
 		goto out;
 	}
 
-- 
2.55.0