[PATCH] mm: stop leaking PageTables
flat view
STALE3578d
From: Hugh Dickins <hughd@google.com>
Date: 2017-01-07 23:37:48
Also in:
linuxppc-dev, lkml
4.10-rc loadtest (even on x86, even without THPCache) fails with
"fork: Cannot allocate memory" or some such; and /proc/meminfo
shows PageTables growing.
rc1 removed the freeing of an unused preallocated pagetable after
do_fault_around() has called map_pages(): which is usually a good
optimization, so that the followup doesn't have to reallocate one;
but it's not sufficient to shift the freeing into alloc_set_pte(),
since there are failure cases (most commonly VM_FAULT_RETRY) which
never reach finish_fault().
Check and free it at the outer level in do_fault(), then we don't
need to worry in alloc_set_pte(), and can restore that to how it was
(I cannot find any reason to pte_free() under lock as it was doing).
And fix a separate pagetable leak, or crash, introduced by the same
change, that could only show up on some ppc64: why does do_set_pmd()'s
failure case attempt to withdraw a pagetable when it never deposited
one, at the same time overwriting (so leaking) the vmf->prealloc_pte?
Residue of an earlier implementation, perhaps? Delete it.
Fixes: 953c66c2b22a ("mm: THP page cache support for ppc64")
Signed-off-by: Hugh Dickins <hughd@google.com>
---
mm/memory.c | 47 ++++++++++++++++++++---------------------------
1 file changed, 20 insertions(+), 27 deletions(-)
--- 4.10-rc2/mm/memory.c 2016-12-25 18:40:50.830453384 -0800
+++ linux/mm/memory.c 2017-01-07 13:34:29.373381551 -0800@@ -3008,13 +3008,6 @@ static int do_set_pmd(struct vm_fault *v ret = 0; count_vm_event(THP_FILE_MAPPED); out: - /* - * If we are going to fallback to pte mapping, do a - * withdraw with pmd lock held. - */ - if (arch_needs_pgtable_deposit() && ret == VM_FAULT_FALLBACK) - vmf->prealloc_pte = pgtable_trans_huge_withdraw(vma->vm_mm, - vmf->pmd); spin_unlock(vmf->ptl); return ret; }
@@ -3055,20 +3048,18 @@ int alloc_set_pte(struct vm_fault *vmf, ret = do_set_pmd(vmf, page); if (ret != VM_FAULT_FALLBACK) - goto fault_handled; + return ret; } if (!vmf->pte) { ret = pte_alloc_one_map(vmf); if (ret) - goto fault_handled; + return ret; } /* Re-check under ptl */ - if (unlikely(!pte_none(*vmf->pte))) { - ret = VM_FAULT_NOPAGE; - goto fault_handled; - } + if (unlikely(!pte_none(*vmf->pte))) + return VM_FAULT_NOPAGE; flush_icache_page(vma, page); entry = mk_pte(page, vma->vm_page_prot);
@@ -3088,15 +3079,8 @@ int alloc_set_pte(struct vm_fault *vmf, /* no need to invalidate: a not-present page won't be cached */ update_mmu_cache(vma, vmf->address, vmf->pte); - ret = 0; -fault_handled: - /* preallocated pagetable is unused: free it */ - if (vmf->prealloc_pte) { - pte_free(vmf->vma->vm_mm, vmf->prealloc_pte); - vmf->prealloc_pte = 0; - } - return ret; + return 0; }
@@ -3360,15 +3344,24 @@ static int do_shared_fault(struct vm_fau static int do_fault(struct vm_fault *vmf) { struct vm_area_struct *vma = vmf->vma; + int ret; /* The VMA was not fully populated on mmap() or missing VM_DONTEXPAND */ if (!vma->vm_ops->fault) - return VM_FAULT_SIGBUS; - if (!(vmf->flags & FAULT_FLAG_WRITE)) - return do_read_fault(vmf); - if (!(vma->vm_flags & VM_SHARED)) - return do_cow_fault(vmf); - return do_shared_fault(vmf); + ret = VM_FAULT_SIGBUS; + else if (!(vmf->flags & FAULT_FLAG_WRITE)) + ret = do_read_fault(vmf); + else if (!(vma->vm_flags & VM_SHARED)) + ret = do_cow_fault(vmf); + else + ret = do_shared_fault(vmf); + + /* preallocated pagetable is unused: free it */ + if (vmf->prealloc_pte) { + pte_free(vma->vm_mm, vmf->prealloc_pte); + vmf->prealloc_pte = 0; + } + return ret; } static int numa_migrate_prep(struct page *page, struct vm_area_struct *vma, --
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