mm/userfaultfd: honor FAULT_FLAG_KILLABLE in fault path

Userfaultfd fault path was by default killable even if the caller does not
have FAULT_FLAG_KILLABLE.  That makes sense before in that when with gup
we don't have FAULT_FLAG_KILLABLE properly set before.  Now after previous
patch we've got FAULT_FLAG_KILLABLE applied even for gup code so it should
also make sense to let userfaultfd to honor the FAULT_FLAG_KILLABLE.

Because we're unconditionally setting FAULT_FLAG_KILLABLE in gup code
right now, this patch should have no functional change.  It also cleaned
the code a little bit by introducing some helpers.
Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Brian Geffon <bgeffon@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Bobby Powers <bobbypowers@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Denis Plotnikov <dplotnikov@virtuozzo.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Martin Cracauer <cracauer@cons.org>
Cc: Marty McFadden <mcfadden8@llnl.gov>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Maya Gokhale <gokhale2@llnl.gov>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Link: http://lkml.kernel.org/r/20200220160300.9941-1-peterx@redhat.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/userfaultfd.c

@@ -334,6 +334,30 @@ static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
 	return ret;
 }
 
+/* Should pair with userfaultfd_signal_pending() */
+static inline long userfaultfd_get_blocking_state(unsigned int flags)
+{
+	if (flags & FAULT_FLAG_INTERRUPTIBLE)
+		return TASK_INTERRUPTIBLE;
+
+	if (flags & FAULT_FLAG_KILLABLE)
+		return TASK_KILLABLE;
+
+	return TASK_UNINTERRUPTIBLE;
+}
+
+/* Should pair with userfaultfd_get_blocking_state() */
+static inline bool userfaultfd_signal_pending(unsigned int flags)
+{
+	if (flags & FAULT_FLAG_INTERRUPTIBLE)
+		return signal_pending(current);
+
+	if (flags & FAULT_FLAG_KILLABLE)
+		return fatal_signal_pending(current);
+
+	return false;
+}
+
 /*
  * The locking rules involved in returning VM_FAULT_RETRY depending on
  * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and
@@ -355,7 +379,7 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
 	struct userfaultfd_ctx *ctx;
 	struct userfaultfd_wait_queue uwq;
 	vm_fault_t ret = VM_FAULT_SIGBUS;
-	bool must_wait, return_to_userland;
+	bool must_wait;
 	long blocking_state;
 
 	/*
@@ -462,9 +486,7 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
 	uwq.ctx = ctx;
 	uwq.waken = false;
 
-	return_to_userland = vmf->flags & FAULT_FLAG_INTERRUPTIBLE;
-	blocking_state = return_to_userland ? TASK_INTERRUPTIBLE :
-			 TASK_KILLABLE;
+	blocking_state = userfaultfd_get_blocking_state(vmf->flags);
 
 	spin_lock_irq(&ctx->fault_pending_wqh.lock);
 	/*
@@ -490,8 +512,7 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
 	up_read(&mm->mmap_sem);
 
 	if (likely(must_wait && !READ_ONCE(ctx->released) &&
-		   (return_to_userland ? !signal_pending(current) :
-		    !fatal_signal_pending(current)))) {
+		   !userfaultfd_signal_pending(vmf->flags))) {
 		wake_up_poll(&ctx->fd_wqh, EPOLLIN);
 		schedule();
 		ret |= VM_FAULT_MAJOR;
@@ -513,8 +534,7 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
 			set_current_state(blocking_state);
 			if (READ_ONCE(uwq.waken) ||
 			    READ_ONCE(ctx->released) ||
-			    (return_to_userland ? signal_pending(current) :
-			     fatal_signal_pending(current)))
+			    userfaultfd_signal_pending(vmf->flags))
 				break;
 			schedule();
 		}