[tip: sched/core] selftests/rseq: Fix: Fail thread registration when CONFIG_RSEQ=n

[tip-bot2 for Mathieu Desnoyers]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     4842dadfc66f627083ec46c4e9a426e805c765f3
Gitweb:        https://git.kernel.org/tip/4842dadfc66f627083ec46c4e9a426e805c765f3
Author:        Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
AuthorDate:    Tue, 22 Nov 2022 15:39:03 -05:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Tue, 27 Dec 2022 12:52:10 +01:00

selftests/rseq: Fix: Fail thread registration when CONFIG_RSEQ=n

When linking the selftests against a libc which does not handle rseq
registration (before 2.35),  rseq thread registration silently succeed
even with CONFIG_RSEQ=n because it erroneously thinks that libc is
handling rseq registration.

This is caused by setting the rseq ownership flag only after the
rseq_available() check. It should rather be set before the
rseq_available() check.

Set the rseq_size to 0 (error value) immediately after the
rseq_available() check fails rather than in the thread registration
functions.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20221122203932.231377-2-mathieu.desnoyers@xxxxxxxxxxxx
---
 tools/testing/selftests/rseq/rseq.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/rseq/rseq.c b/tools/testing/selftests/rseq/rseq.c
index 4177f95..376a73f 100644
--- a/tools/testing/selftests/rseq/rseq.c
+++ b/tools/testing/selftests/rseq/rseq.c
@@ -119,9 +119,11 @@ void rseq_init(void)
 		rseq_flags = *libc_rseq_flags_p;
 		return;
 	}
-	if (!rseq_available())
-		return;
 	rseq_ownership = 1;
+	if (!rseq_available()) {
+		rseq_size = 0;
+		return;
+	}
 	rseq_offset = (void *)&__rseq_abi - rseq_thread_pointer();
 	rseq_size = sizeof(struct rseq_abi);
 	rseq_flags = 0;