[BUG] inotify_add_watch/inotify_rm_watch loops trigger oom

[Eryu Guan <guaneryu@gmail.com>]

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Hi,

Starting from v4.5-rc1 running inotify_add_watch/inotify_rm_watch in
loop could trigger OOM and system becomes unusuable. v4.4 kernel is fine
with the same stress test.

Reverting c510eff6beba ("fsnotify: destroy marks with call_srcu instead
of dedicated thread") on top of v4.5-rc3 passed the same test, seems
that this patch introduced some kind of memleak?

On v4.5-rc[1-3] the test program triggers oom within 10 minutes on my
test vm with 8G mem.  After reverting the commit in question the same vm
survived more than 1 hour stress test.

	./inotify <mnt>

I attached the test program and oom console log. If more information is
needed please let me know.

Thanks,
Eryu

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#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/inotify.h>

int main(int argc, char *argv[])
{
	int notify_fd;
	int wd, ret;

	notify_fd = inotify_init();

	for (;;) {
		wd = inotify_add_watch(notify_fd, argv[1], IN_MODIFY | IN_CREATE | IN_DELETE );
		if (wd < 0) {
			perror("inotify_add_watch");
		}
		ret = inotify_rm_watch(notify_fd, wd);
		if (ret < 0) {
			perror("inotify_rm_watch");
		}
	}
out:
	close(notify_fd);

	return 0;
}

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