Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Peter Xu <peterx@redhat.com>
To:     linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc:     Peter Xu <peterx@redhat.com>, Martin Cracauer <cracauer@cons.org>,
        Mike Rapoport <rppt@linux.vnet.ibm.com>,
        Hugh Dickins <hughd@google.com>,
        Jerome Glisse <jglisse@redhat.com>,
        "Kirill A . Shutemov" <kirill@shutemov.name>,
        Matthew Wilcox <willy@infradead.org>,
        Pavel Emelyanov <xemul@virtuozzo.com>,
        Brian Geffon <bgeffon@google.com>,
        Maya Gokhale <gokhale2@llnl.gov>,
        Denis Plotnikov <dplotnikov@virtuozzo.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Marty McFadden <mcfadden8@llnl.gov>,
        David Hildenbrand <david@redhat.com>,
        Bobby Powers <bobbypowers@gmail.com>,
        Mel Gorman <mgorman@suse.de>
Subject: [PATCH RESEND v6 09/16] mm: Return faster for non-fatal signals in user mode faults
Date:   Thu, 20 Feb 2020 11:02:30 -0500
Message-Id: <20200220160230.9598-1-peterx@redhat.com>
In-Reply-To: <20200220155353.8676-1-peterx@redhat.com>
References: 
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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

  https://lore.kernel.org/lkml/20171102193644.GB22686@redhat.com/

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.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Suggested-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 include/linux/sched/signal.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index 4c87ffce64d1..09d40ce6a162 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -379,7 +379,8 @@ static inline bool fault_signal_pending(unsigned int fault_flags,
 					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))));
 }
 
 /*
-- 
2.24.1