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mm: Close races between THP migration and PMD numa clearing

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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>
This commit is contained in:
Mel Gorman
2013-10-07 11:28:46 +01:00
committed by Ingo Molnar
parent 8191acbd30
commit a54a407fbf
2 changed files with 26 additions and 26 deletions
Download Patch File Download Diff File Expand all files Collapse all files

33
mm/huge_memory.c
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@@ -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);