pnfsblock: acquire im_lock in _preload_range
pnfsblock: acquire im_lock in _preload_range

When calling _add_entry, we should take the im_lock to protect
agains other modifiers.

Cc: <4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@vger.kernel.org> #3.1+
Signed-off-by: Peng Tao <bcb6f79e065432a38332d10b078989bd37522edc@emc.com>
Signed-off-by: Benny Halevy <23c997c90eb8537635e9392d48e7af1bf1b2ca22@tonian.com>
Signed-off-by: Trond Myklebust <6a1f9db795c9fc44be97d66ab114c53193bd3d13@netapp.com>

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