CHROMIUM: android: binder: Fix potential scheduling-while-atomic

Commit f1e7f0a ("android: binder: Disable preemption while holding
the global binder lock.") re-enabled preemption around most of the sites
where calls to potentially sleeping functions were made, but missed
__alloc_fd(), which can sleep if the fdtable needs to be resized.
Re-enable preemption around __alloc_fd() as well as __fd_install() which
can now sleep in upstream kernels as of commit 8a81252 ("fs/file.c:
don't acquire files->file_lock in fd_install()").

BUG=chrome-os-partner:44012
TEST=Build and boot on Smaug.

Change-Id: I9819c4b95876f697e75b1b84810b6c520d9c33ec
Signed-off-by: Andrew Bresticker <abrestic@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/308582
Reviewed-by: Stephen Barber <smbarber@chromium.org>
Reviewed-by: Riley Andrews <riandrews@google.com>

drivers/staging/android/binder.c

@@ -375,6 +375,7 @@ static int task_get_unused_fd_flags(struct binder_proc *proc, int flags)
 	struct files_struct *files = proc->files;
 	unsigned long rlim_cur;
 	unsigned long irqs;
+	int ret;
 
 	if (files == NULL)
 		return -ESRCH;
@@ -385,7 +386,11 @@ static int task_get_unused_fd_flags(struct binder_proc *proc, int flags)
 	rlim_cur = task_rlimit(proc->tsk, RLIMIT_NOFILE);
 	unlock_task_sighand(proc->tsk, &irqs);
 
-	return __alloc_fd(files, 0, rlim_cur, flags);
+	preempt_enable_no_resched();
+	ret = __alloc_fd(files, 0, rlim_cur, flags);
+	preempt_disable();
+
+	return ret;
 }
 
 /*
@@ -394,8 +399,11 @@ static int task_get_unused_fd_flags(struct binder_proc *proc, int flags)
 static void task_fd_install(
 	struct binder_proc *proc, unsigned int fd, struct file *file)
 {
-	if (proc->files)
+	if (proc->files) {
+		preempt_enable_no_resched();
 		__fd_install(proc->files, fd, file);
+		preempt_disable();
+	}
 }
 
 /*