The patch titled
Subject: mm: change mm_update_next_owner() to update mm->owner with WRITE_ONCE
has been added to the -mm tree. Its filename is
mm-change-mm_update_next_owner-to-update-mm-owner-with-write_once.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-change-mm_update_next_owner-to-update-mm-owner-with-write_once.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-change-mm_update_next_owner-to-update-mm-owner-with-write_once.patch
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------------------------------------------------------
From: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Subject: mm: change mm_update_next_owner() to update mm->owner with WRITE_ONCE
The RCU reader uses rcu_dereference() inside rcu_read_lock critical
sections, so the writer shall use WRITE_ONCE. Just a cleanup, we still
rely on gcc to emit atomic writes in other places.
Link: http://lkml.kernel.org/r/20190325225636.11635-3-aarcange@xxxxxxxxxx
Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
Cc: "Kirill A . Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: zhong jiang <zhongjiang@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/exit.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
--- a/kernel/exit.c~mm-change-mm_update_next_owner-to-update-mm-owner-with-write_once
+++ a/kernel/exit.c
@@ -422,7 +422,7 @@ retry:
* freed task structure.
*/
if (atomic_read(&mm->mm_users) <= 1) {
- mm->owner = NULL;
+ WRITE_ONCE(mm->owner, NULL);
return;
}
@@ -462,7 +462,7 @@ retry:
* most likely racing with swapoff (try_to_unuse()) or /proc or
* ptrace or page migration (get_task_mm()). Mark owner as NULL.
*/
- mm->owner = NULL;
+ WRITE_ONCE(mm->owner, NULL);
return;
assign_new_owner:
@@ -483,7 +483,7 @@ assign_new_owner:
put_task_struct(c);
goto retry;
}
- mm->owner = c;
+ WRITE_ONCE(mm->owner, c);
task_unlock(c);
put_task_struct(c);
}
_
Patches currently in -mm which might be from aarcange@xxxxxxxxxx are
coredump-fix-race-condition-between-mmget_not_zero-get_task_mm-and-core-dumping.patch
userfaultfd-use-rcu-to-free-the-task-struct-when-fork-fails.patch
mm-change-mm_update_next_owner-to-update-mm-owner-with-write_once.patch
