locking, fs/locks: Add missing file_sem locks

I overlooked a few code-paths that can lead to
locks_delete_global_locks().
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Jeff Layton <jlayton@poochiereds.net>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Bruce Fields <bfields@fieldses.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-fsdevel@vger.kernel.org
Cc: syzkaller <syzkaller@googlegroups.com>
Link: http://lkml.kernel.org/r/20161008081228.GF3142@twins.programming.kicks-ass.netSigned-off-by: Ingo Molnar <mingo@kernel.org>

fs/locks.c

@@ -1609,6 +1609,7 @@ int fcntl_getlease(struct file *filp)
 
 	ctx = smp_load_acquire(&inode->i_flctx);
 	if (ctx && !list_empty_careful(&ctx->flc_lease)) {
+		percpu_down_read_preempt_disable(&file_rwsem);
 		spin_lock(&ctx->flc_lock);
 		time_out_leases(inode, &dispose);
 		list_for_each_entry(fl, &ctx->flc_lease, fl_list) {
@@ -1618,6 +1619,8 @@ int fcntl_getlease(struct file *filp)
 			break;
 		}
 		spin_unlock(&ctx->flc_lock);
+		percpu_up_read_preempt_enable(&file_rwsem);
+
 		locks_dispose_list(&dispose);
 	}
 	return type;
@@ -2529,11 +2532,14 @@ locks_remove_lease(struct file *filp, struct file_lock_context *ctx)
 	if (list_empty(&ctx->flc_lease))
 		return;
 
+	percpu_down_read_preempt_disable(&file_rwsem);
 	spin_lock(&ctx->flc_lock);
 	list_for_each_entry_safe(fl, tmp, &ctx->flc_lease, fl_list)
 		if (filp == fl->fl_file)
 			lease_modify(fl, F_UNLCK, &dispose);
 	spin_unlock(&ctx->flc_lock);
+	percpu_up_read_preempt_enable(&file_rwsem);
+
 	locks_dispose_list(&dispose);
 }