[GIT PULL] sysctl fixes for v4.13-rc1

[Eric W. Biederman]

Linus,

Please pull the for-linus branch from the git tree:

   git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git for-linus

   HEAD: 2fd1d2c4ceb2248a727696962cf3370dc9f5a0a4 proc: Fix proc_sys_prune_dcache to hold a sb reference

A rather embarassing and hard to hit bug was merged into 4.11-rc1.
Andrei Vagin tracked this bug now and after some starting at the
code I came up with a fix.

Eric