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authorMel Gorman <mgorman@suse.de>2013-10-07 11:28:46 +0100
committerIngo Molnar <mingo@kernel.org>2013-10-09 12:39:45 +0200
commita54a407fbf7735fd8f7841375574f5d9b0375f93 (patch)
tree29a4af92708dfc99f1693e9a313b53474d50c496 /mm/huge_memory.c
parent8191acbd30c73e45c24ad16c372e0b42cc7ac8f8 (diff)
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>
Diffstat (limited to 'mm/huge_memory.c')
-rw-r--r--mm/huge_memory.c33
1 files changed, 15 insertions, 18 deletions
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index c3bb65f284d5..d4928769680f 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1304,24 +1304,25 @@ int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
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 @@ int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
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);