On 2017/6/19 12:48, Andy Lutomirski wrote: > It was historically possible to have two concurrent TLB flushes > targeting the same CPU: one initiated locally and one initiated > remotely. This can now cause an OOPS in leave_mm() at > arch/x86/mm/tlb.c:47: > > if (this_cpu_read(cpu_tlbstate.state) == TLBSTATE_OK) > BUG(); > > with this call trace: > flush_tlb_func_local arch/x86/mm/tlb.c:239 [inline] > flush_tlb_mm_range+0x26d/0x370 arch/x86/mm/tlb.c:317 > > Without reentrancy, this OOPS is impossible: leave_mm() is only > called if we're not in TLBSTATE_OK, but then we're unexpectedly > in TLBSTATE_OK in leave_mm(). > > This can be caused by flush_tlb_func_remote() happening between > the two checks and calling leave_mm(), resulting in two consecutive > leave_mm() calls on the same CPU with no intervening switch_mm() > calls. > > We never saw this OOPS before because the old leave_mm() > implementation didn't put us back in TLBSTATE_OK, so the assertion > didn't fire. HI, Andy
Today, I see same OOPS in linux 3.4 stable. It prove that it indeed has fired. but It is rarely to appear. I review the code. I found the a issue. when current->mm is NULL, leave_mm will be called. but it maybe in TLBSTATE_OK, eg: unuse_mm call after task->mm = NULL , but before enter_lazy_tlb. therefore, it will fire. is it right? Thanks zhongjiang > Nadav noticed the reentrancy issue in a different context, but > neither of us realized that it caused a problem yet. > > Cc: Nadav Amit <nadav.a...@gmail.com> > Cc: Dave Hansen <dave.han...@intel.com> > Reported-by: "Levin, Alexander (Sasha Levin)" <alexander.le...@verizon.com> > Fixes: 3d28ebceaffa ("x86/mm: Rework lazy TLB to track the actual loaded mm") > Signed-off-by: Andy Lutomirski <l...@kernel.org> > --- > arch/x86/mm/tlb.c | 15 +++++++++++++-- > 1 file changed, 13 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c > index 2a5e851f2035..f06239c6919f 100644 > --- a/arch/x86/mm/tlb.c > +++ b/arch/x86/mm/tlb.c > @@ -208,6 +208,9 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct > mm_struct *next, > static void flush_tlb_func_common(const struct flush_tlb_info *f, > bool local, enum tlb_flush_reason reason) > { > + /* This code cannot presently handle being reentered. */ > + VM_WARN_ON(!irqs_disabled()); > + > if (this_cpu_read(cpu_tlbstate.state) != TLBSTATE_OK) { > leave_mm(smp_processor_id()); > return; > @@ -313,8 +316,12 @@ void flush_tlb_mm_range(struct mm_struct *mm, unsigned > long start, > info.end = TLB_FLUSH_ALL; > } > > - if (mm == this_cpu_read(cpu_tlbstate.loaded_mm)) > + if (mm == this_cpu_read(cpu_tlbstate.loaded_mm)) { > + local_irq_disable(); > flush_tlb_func_local(&info, TLB_LOCAL_MM_SHOOTDOWN); > + local_irq_enable(); > + } > + > if (cpumask_any_but(mm_cpumask(mm), cpu) < nr_cpu_ids) > flush_tlb_others(mm_cpumask(mm), &info); > put_cpu(); > @@ -370,8 +377,12 @@ void arch_tlbbatch_flush(struct > arch_tlbflush_unmap_batch *batch) > > int cpu = get_cpu(); > > - if (cpumask_test_cpu(cpu, &batch->cpumask)) > + if (cpumask_test_cpu(cpu, &batch->cpumask)) { > + local_irq_disable(); > flush_tlb_func_local(&info, TLB_LOCAL_SHOOTDOWN); > + local_irq_enable(); > + } > + > if (cpumask_any_but(&batch->cpumask, cpu) < nr_cpu_ids) > flush_tlb_others(&batch->cpumask, &info); > cpumask_clear(&batch->cpumask);