[LTP] [PATCH 2/2] syscalls/inotify06: Raise inotify instance limit in /proc

[Jan Kara]

On Wed 05-05-21 17:38:47, Martin Doucha wrote:
> inotify_init() sometimes fails with EMFILE because there are too many
> partially closed instances waiting for garbage collection. Bump the limit
> in /proc/sys/fs/inotify/max_user_instances for the duration of the test.
> 
> Signed-off-by: Martin Doucha <mdoucha@suse.cz>
> ---
> 
> I thought about only reading the procfile and calling yield() after every
> proc_limit/2 iterations to wait for garbage collection but I'm afraid that
> it might reduce the likelihood of triggering the bug. Since I currently have
> no system where I could reproduce the race, I've decided to play it safe and
> bump the /proc limit.

So waiting would be fine as well. One process simply creates & deletes
files in a loop until the other performs TEARDOWNS teardowns. It doesn't
really matter how fast teardowns happen for the race to trigger. But I have
no problem with this solution either.

								Honza

> 
>  testcases/kernel/syscalls/inotify/inotify06.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/testcases/kernel/syscalls/inotify/inotify06.c b/testcases/kernel/syscalls/inotify/inotify06.c
> index f39ab46a1..68813769b 100644
> --- a/testcases/kernel/syscalls/inotify/inotify06.c
> +++ b/testcases/kernel/syscalls/inotify/inotify06.c
> @@ -38,8 +38,11 @@
>  /* Number of files to test (must be > 1) */
>  #define FILES 5
>  
> +#define PROCFILE "/proc/sys/fs/inotify/max_user_instances"
> +
>  static char names[FILES][PATH_MAX];
>  static pid_t pid;
> +static int old_proc_limit;
>  
>  static void setup(void)
>  {
> @@ -47,6 +50,11 @@ static void setup(void)
>  
>  	for (i = 0; i < FILES; i++)
>  		sprintf(names[i], "fname_%d", i);
> +
> +	SAFE_FILE_SCANF(PROCFILE, "%d", &old_proc_limit);
> +
> +	if (old_proc_limit >= 0 && old_proc_limit < TEARDOWNS)
> +		SAFE_FILE_PRINTF(PROCFILE, "%d", TEARDOWNS + 128);
>  }
>  
>  static void verify_inotify(void)
> @@ -95,10 +103,13 @@ static void cleanup(void)
>  		SAFE_KILL(pid, SIGKILL);
>  		SAFE_WAIT(NULL);
>  	}
> +
> +	SAFE_FILE_PRINTF(PROCFILE, "%d", old_proc_limit);
>  }
>  
>  static struct tst_test test = {
>  	.timeout = 600,
> +	.needs_root = 1,
>  	.needs_tmpdir = 1,
>  	.forks_child = 1,
>  	.setup = setup,
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR