knfsd: use a spinlock to protect sk_info_authunix
knfsd: use a spinlock to protect sk_info_authunix

sk_info_authunix is not being protected properly so the object that it
points to can be cache_put twice, leading to corruption.

We borrow svsk->sk_defer_lock to provide the protection.  We should
probably rename that lock to have a more generic name - later.

Thanks to Gabriel for reporting this.

Cc: Greg Banks <3c474cf4bdc26bce6c823d6384748a5a3679f008@melbourne.sgi.com>
Cc: Gabriel Barazer <18a98c35f49808b45edadc75fb1b25ebfd4037d6@oxeva.fr>
Signed-off-by: Neil Brown <1c00aa603bb92d594c03cff60ecf8e63b2a5bcb1@suse.de>
Cc: <4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@kernel.org>
Signed-off-by: Andrew Morton <5c1e68b099950c134891f0b6e179498a8ebe9cf9@linux-foundation.org>
Signed-off-by: Linus Torvalds <69652caca27c8b940640ad396ab71f93cacec34f@linux-foundation.org>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs