Messages in this thread Patch in this message | | | From | Samu Kallio <> | Subject | [PATCH] x86: mm: Fix vmalloc_fault oops during lazy MMU updates | Date | Thu, 21 Feb 2013 03:45:33 +0200 |
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In paravirtualized x86_64 kernels, vmalloc_fault may cause an oops when lazy MMU updates are enabled, because set_pgd effects are being deferred.
One instance of this problem is during process mm cleanup with memory cgroups enabled. The chain of events is as follows:
- zap_pte_range enables lazy MMU updates - zap_pte_range eventually calls mem_cgroup_charge_statistics, which accesses the vmalloc'd mem_cgroup per-cpu stat area - vmalloc_fault is triggered which tries to sync the corresponding PGD entry with set_pgd, but the update is deferred - vmalloc_fault oopses due to a mismatch in the PUD entries
Calling arch_flush_lazy_mmu_mode immediately after set_pgd makes the changes visible to the consistency checks.
Signed-off-by: Samu Kallio <samu.kallio@aberdeencloud.com> --- arch/x86/mm/fault.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 027088f..3ba3dba 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -378,10 +378,12 @@ static noinline __kprobes int vmalloc_fault(unsigned long address) if (pgd_none(*pgd_ref)) return -1; - if (pgd_none(*pgd)) + if (pgd_none(*pgd)) { set_pgd(pgd, *pgd_ref); - else + arch_flush_lazy_mmu_mode(); + } else { BUG_ON(pgd_page_vaddr(*pgd) != pgd_page_vaddr(*pgd_ref)); + } /* * Below here mismatches are bugs because these lower tables -- 1.8.1.3
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