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

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Message-ID: <YkIe1Kr0w2vXUQuN@pevik>
Date:   Mon, 28 Mar 2022 22:47:16 +0200
From:   Petr Vorel <pvorel@...e.cz>
To:     linux-kernel@...r.kernel.org
Cc:     Cyril Hrubis <chrubis@...e.cz>,
        Andrea Cervesato <andrea.cervesato@...e.de>
Subject: Re: [PATCH v2 1/1] lib: Retry safe_clone() on ENOSPC|EUSERS

Oops, wrong list, sorry.

Kind regards,
Petr

> 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: