linux-kernel - [PATCH v2 1/1] lib: Retry safe

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Message-Id: <20220328204554.2528-1-pvorel@suse.cz>
Date:   Mon, 28 Mar 2022 22:45:54 +0200
From:   Petr Vorel <pvorel@...e.cz>
To:     linux-kernel@...r.kernel.org
Cc:     Petr Vorel <pvorel@...e.cz>, Cyril Hrubis <chrubis@...e.cz>,
        Andrea Cervesato <andrea.cervesato@...e.de>
Subject: [PATCH v2 1/1] lib: Retry safe_clone() on ENOSPC|EUSERS

In some tests we are creating the namespaces faster than they are being
asynchronously cleaned up in the kernel:

$ sudo ./userns08 -i 10
userns08.c:65: TPASS: Denied write access to ./restricted : EACCES (13)
userns08.c:65: TPASS: Denied write access to ./restricted : EACCES (13)
userns08.c:65: TPASS: Denied write access to ./restricted : EACCES (13)
userns08.c:65: TPASS: Denied write access to ./restricted : EACCES (13)
userns08.c:65: TPASS: Denied write access to ./restricted : EACCES (13)
userns08.c:36: TBROK: clone3 failed: ENOSPC (28)

Thus retrying the clone() on ENOSPC (or EUSERS for kernel < 4.9).

Suggested-by: Cyril Hrubis <chrubis@...e.cz>
Signed-off-by: Petr Vorel <pvorel@...e.cz>
---
changes v1->v2:
* use TST_RETRY_FN_EXP_BACKOFF() (Cyril)

NOTE: 0.1s seems to be safe, although using TST_RETRY_FUNC() with 1s
(the default) would be of course OK.

Kind regards,
Petr

 lib/tst_test.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/lib/tst_test.c b/lib/tst_test.c
index 384c73e163..2e89d954ec 100644
--- a/lib/tst_test.c
+++ b/lib/tst_test.c
@@ -436,6 +436,9 @@ pid_t safe_fork(const char *filename, unsigned int lineno)
 	return pid;
 }
 
+/* too fast creating namespaces => retrying */
+#define TST_CHECK_ENOSPC(x) ((x) >= 0 || !(errno == ENOSPC || errno == EUSERS))
+
 pid_t safe_clone(const char *file, const int lineno,
 		 const struct tst_clone_args *args)
 {
@@ -444,7 +447,7 @@ pid_t safe_clone(const char *file, const int lineno,
 	if (!tst_test->forks_child)
 		tst_brk(TBROK, "test.forks_child must be set!");
 
-	pid = tst_clone(args);
+	pid = TST_RETRY_FN_EXP_BACKOFF(tst_clone(args), TST_CHECK_ENOSPC, 0.1);
 
 	switch (pid) {
 	case -1:
-- 
2.35.1