mm: Close races between THP migration and PMD numa clearing
THP migration uses the page lock to guard against parallel allocations
but there are cases like this still open
Task A Task B
--------------------- ---------------------
do_huge_pmd_numa_page do_huge_pmd_numa_page
lock_page
mpol_misplaced == -1
unlock_page
goto clear_pmdnuma
lock_page
mpol_misplaced == 2
migrate_misplaced_transhuge
pmd = pmd_mknonnuma
set_pmd_at
During hours of testing, one crashed with weird errors and while I have
no direct evidence, I suspect something like the race above happened.
This patch extends the page lock to being held until the pmd_numa is
cleared to prevent migration starting in parallel while the pmd_numa is
being cleared. It also flushes the old pmd entry and orders pagetable
insertion before rmap insertion.
Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1381141781-10992-9-git-send-email-mgorman@suse.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index c3bb65f..d4928769 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1304,24 +1304,25 @@
target_nid = mpol_misplaced(page, vma, haddr);
if (target_nid == -1) {
/* If the page was locked, there are no parallel migrations */
- if (page_locked) {
- unlock_page(page);
+ if (page_locked)
goto clear_pmdnuma;
- }
- /* Otherwise wait for potential migrations and retry fault */
+ /*
+ * Otherwise wait for potential migrations and retry. We do
+ * relock and check_same as the page may no longer be mapped.
+ * As the fault is being retried, do not account for it.
+ */
spin_unlock(&mm->page_table_lock);
wait_on_page_locked(page);
+ page_nid = -1;
goto out;
}
/* Page is misplaced, serialise migrations and parallel THP splits */
get_page(page);
spin_unlock(&mm->page_table_lock);
- if (!page_locked) {
+ if (!page_locked)
lock_page(page);
- page_locked = true;
- }
anon_vma = page_lock_anon_vma_read(page);
/* Confirm the PMD did not change while page_table_lock was released */
@@ -1329,32 +1330,28 @@
if (unlikely(!pmd_same(pmd, *pmdp))) {
unlock_page(page);
put_page(page);
+ page_nid = -1;
goto out_unlock;
}
- /* Migrate the THP to the requested node */
+ /*
+ * Migrate the THP to the requested node, returns with page unlocked
+ * and pmd_numa cleared.
+ */
spin_unlock(&mm->page_table_lock);
migrated = migrate_misplaced_transhuge_page(mm, vma,
pmdp, pmd, addr, page, target_nid);
if (migrated)
page_nid = target_nid;
- else
- goto check_same;
goto out;
-
-check_same:
- spin_lock(&mm->page_table_lock);
- if (unlikely(!pmd_same(pmd, *pmdp))) {
- /* Someone else took our fault */
- page_nid = -1;
- goto out_unlock;
- }
clear_pmdnuma:
+ BUG_ON(!PageLocked(page));
pmd = pmd_mknonnuma(pmd);
set_pmd_at(mm, haddr, pmdp, pmd);
VM_BUG_ON(pmd_numa(*pmdp));
update_mmu_cache_pmd(vma, addr, pmdp);
+ unlock_page(page);
out_unlock:
spin_unlock(&mm->page_table_lock);