[Devel] [PATCH RHEL8 COMMIT] mm/gup: allow to react to fatal signals

[Konstantin Khorenko]

The commit is pushed to "branch-rh8-4.18.0-80.1.2.vz8.3.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh8-4.18.0-80.1.2.vz8.3.6
------>
commit 16f743d9a59c9505b2166b2d463e145409abba23
Author: Peter Xu <peterx at redhat.com>
Date:   Mon Apr 20 10:34:24 2020 +0300

    mm/gup: allow to react to fatal signals
    
    The existing gup code does not react to the fatal signals in many code
    paths.  For example, in one retry path of gup we're still using
    down_read() rather than down_read_killable().  Also, when doing page
    faults we don't pass in FAULT_FLAG_KILLABLE as well, which means that
    within the faulting process we'll wait in non-killable way as well.  These
    were spotted by Linus during the code review of some other patches.
    
    Let's allow the gup code to react to fatal signals to improve the
    responsiveness of threads when during gup and being killed.
    
    Signed-off-by: Peter Xu <peterx at redhat.com>
    Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
    Tested-by: Brian Geffon <bgeffon at google.com>
    Cc: Andrea Arcangeli <aarcange at redhat.com>
    Cc: Bobby Powers <bobbypowers at gmail.com>
    Cc: David Hildenbrand <david at redhat.com>
    Cc: Denis Plotnikov <dplotnikov at virtuozzo.com>
    Cc: "Dr . David Alan Gilbert" <dgilbert at redhat.com>
    Cc: Hugh Dickins <hughd at google.com>
    Cc: Jerome Glisse <jglisse at redhat.com>
    Cc: Johannes Weiner <hannes at cmpxchg.org>
    Cc: "Kirill A . Shutemov" <kirill at shutemov.name>
    Cc: Martin Cracauer <cracauer at cons.org>
    Cc: Marty McFadden <mcfadden8 at llnl.gov>
    Cc: Matthew Wilcox <willy at infradead.org>
    Cc: Maya Gokhale <gokhale2 at llnl.gov>
    Cc: Mel Gorman <mgorman at suse.de>
    Cc: Mike Kravetz <mike.kravetz at oracle.com>
    Cc: Mike Rapoport <rppt at linux.vnet.ibm.com>
    Cc: Pavel Emelyanov <xemul at openvz.org>
    Link: http://lkml.kernel.org/r/20200220160256.9887-1-peterx@redhat.com
    Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
    
    https://jira.sw.ru/browse/PSBM-102938
    (cherry picked from commit 71335f37c5e8ec9225285206f7f875057b9737ad)
    Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 mm/gup.c     | 12 +++++++++---
 mm/hugetlb.c |  3 ++-
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index cdf438ea8621..3d08b68c210f 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -507,7 +507,7 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
 	if (*flags & FOLL_REMOTE)
 		fault_flags |= FAULT_FLAG_REMOTE;
 	if (locked)
-		fault_flags |= FAULT_FLAG_ALLOW_RETRY;
+		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
 	if (*flags & FOLL_NOWAIT)
 		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;
 	if (*flags & FOLL_TRIED) {
@@ -832,7 +832,7 @@ int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
 	int ret, major = 0;
 
 	if (unlocked)
-		fault_flags |= FAULT_FLAG_ALLOW_RETRY;
+		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
 
 retry:
 	vma = find_extend_vma(mm, address);
@@ -945,7 +945,13 @@ static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
 			break;
 
 		*locked = 1;
-		down_read(&mm->mmap_sem);
+		ret = down_read_killable(&mm->mmap_sem);
+		if (ret) {
+			BUG_ON(ret > 0);
+			if (!pages_done)
+				pages_done = ret;
+			break;
+		}
 
 		ret = __get_user_pages(tsk, mm, start, 1, flags | FOLL_TRIED,
 				       pages, NULL, locked);
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 417b96f4aa14..ec839cd22a3f 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4223,7 +4223,8 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 			if (flags & FOLL_WRITE)
 				fault_flags |= FAULT_FLAG_WRITE;
 			if (locked)
-				fault_flags |= FAULT_FLAG_ALLOW_RETRY;
+				fault_flags |= FAULT_FLAG_ALLOW_RETRY |
+					FAULT_FLAG_KILLABLE;
 			if (flags & FOLL_NOWAIT)
 				fault_flags |= FAULT_FLAG_ALLOW_RETRY |
 					FAULT_FLAG_RETRY_NOWAIT;