[094/155] mm: return faster for non-fatal signals in user mode faults

Commit Message

Andrew Morton April 2, 2020, 4:08 a.m. UTC

From: Peter Xu <[e-mail]>
Subject: mm: return faster for non-fatal signals in user mode faults

The idea comes from the upstream discussion between Linus and Andrea:

  https://lore.kernel.org/lkml/[e-mail]/

A summary to the issue: there was a special path in handle_userfault() in
the past that we'll return a VM_FAULT_NOPAGE when we detected non-fatal
signals when waiting for userfault handling.  We did that by reacquiring
the mmap_sem before returning.  However that brings a risk in that the
vmas might have changed when we retake the mmap_sem and even we could be
holding an invalid vma structure.

This patch is a preparation of removing that special path by allowing the
page fault to return even faster if we were interrupted by a non-fatal
signal during a user-mode page fault handling routine.

Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Peter Xu <[e-mail]>
Suggested-by: Linus Torvalds <[e-mail]>
Suggested-by: Andrea Arcangeli <[e-mail]>
Tested-by: Brian Geffon <[e-mail]>
Cc: Bobby Powers <[e-mail]>
Cc: David Hildenbrand <[e-mail]>
Cc: Denis Plotnikov <[e-mail]>
Cc: "Dr . David Alan Gilbert" <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: Jerome Glisse <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: "Kirill A . Shutemov" <[e-mail]>
Cc: Martin Cracauer <[e-mail]>
Cc: Marty McFadden <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Cc: Maya Gokhale <[e-mail]>
Cc: Mel Gorman <[e-mail]>
Cc: Mike Kravetz <[e-mail]>
Cc: Mike Rapoport <[e-mail]>
Cc: Pavel Emelyanov <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 include/linux/sched/signal.h |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Patch

--- a/include/linux/sched/signal.h~mm-return-faster-for-non-fatal-signals-in-user-mode-faults
+++ a/include/linux/sched/signal.h
@@ -381,7 +381,8 @@  static inline bool fault_signal_pending(
 					struct pt_regs *regs)
 {
 	return unlikely((fault_flags & VM_FAULT_RETRY) &&
-			fatal_signal_pending(current));
+			(fatal_signal_pending(current) ||
+			 (user_mode(regs) && signal_pending(current))));
 }
 
 /*