The patch titled
fix migration_entry_wait() for speculative page cache
has been added to the -mm tree. Its filename is
mm-speculative-page-references-fix-migration_entry_wait-for-speculative-page-cache.patch
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------------------------------------------------------
Subject: fix migration_entry_wait() for speculative page cache
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
In speculative page cache lookup protocol, page_count(page) is set to 0
while radix-tree modification is going on, truncation, migration, etc...
While page migration, a page fault to page under migration should wait
unlock_page() and migration_entry_wait() waits for the page from its pte
entry. It does get_page() -> wait_on_page_locked() -> put_page() now.
In page migration, page_freeze_refs() -> page_unfreeze_refs() is called.
Here, page_unfreeze_refs() expects page_count(page) == 0 and panics if
page_count(page) != 0. To avoid this, we shouldn't touch page_count() if
it is zero. This patch uses page_cache_get_speculative() to avoid the
panic.
Signed-off-by: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Nick Piggin <nickpiggin@xxxxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/migrate.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff -puN mm/migrate.c~mm-speculative-page-references-fix-migration_entry_wait-for-speculative-page-cache mm/migrate.c
--- a/mm/migrate.c~mm-speculative-page-references-fix-migration_entry_wait-for-speculative-page-cache
+++ a/mm/migrate.c
@@ -285,7 +285,15 @@ void migration_entry_wait(struct mm_stru
page = migration_entry_to_page(entry);
- get_page(page);
+ /*
+ * Once radix-tree replacement of page migration started, page_count
+ * *must* be zero. And, we don't want to call wait_on_page_locked()
+ * against a page without get_page().
+ * So, we use get_page_unless_zero(), here. Even failed, page fault
+ * will occur again.
+ */
+ if (!get_page_unless_zero(page))
+ goto out;
pte_unmap_unlock(ptep, ptl);
wait_on_page_locked(page);
put_page(page);
_
Patches currently in -mm which might be from kamezawa.hiroyu@xxxxxxxxxxxxxx are
page-flags-record-page-flag-overlays-explicitly.patch
page-flags-record-page-flag-overlays-explicitly-xen.patch
mark-res_counter_charge_locked-with-__must_check.patch
cgroup-files-clean-up-whitespace-in-struct-cftype.patch
cgroup-files-add-write_string-cgroup-control-file-method.patch
cgroup-files-move-the-release_agent-file-to-use-typed-handlers.patch
cgroup-files-move-notify_on_release-file-to-separate-write-handler.patch
cgroup-files-turn-attach_task_by_pid-directly-into-a-cgroup-write-handler.patch
cgroup-files-remove-cpuset_common_file_write.patch
cgroup-files-convert-devcgroup_access_write-into-a-cgroup-write_string-handler.patch
cgroup-files-convert-res_counter_write-to-be-a-cgroups-write_string-handler.patch
memcg-make-global-var-read_mostly.patch
memcg-avoid-unnecessary-initialization.patch
memcg-better-migration-handling.patch
memcg-remove-refcnt-from-page_cgroup.patch
memcg-remove-refcnt-from-page_cgroup-fix.patch
memcg-remove-refcnt-from-page_cgroup-fix-2.patch
memcg-handle-swap-cache.patch
memcg-handle-swap-cache-fix.patch
memcg-helper-function-for-relcaim-from-shmem.patch
memcg-add-hints-for-branch.patch
memcg-remove-a-redundant-check.patch
memcg-clean-up-checking-of-the-disabled-flag.patch
memrlimit-add-memrlimit-controller-documentation.patch
memrlimit-setup-the-memrlimit-controller.patch
memrlimit-cgroup-mm-owner-callback-changes-to-add-task-info.patch
memrlimit-add-memrlimit-controller-accounting-and-control.patch
mm-speculative-page-references-fix-migration_entry_wait-for-speculative-page-cache.patch
fix-double-unlock_page-in-2626-rc5-mm3-kernel-bug-at-mm-filemapc-575.patch
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