Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753287AbdFUFWk (ORCPT ); Wed, 21 Jun 2017 01:22:40 -0400 Received: from mail.kernel.org ([198.145.29.99]:55578 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753240AbdFUFWb (ORCPT ); Wed, 21 Jun 2017 01:22:31 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3DAD323A07 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=luto@kernel.org From: Andy Lutomirski To: x86@kernel.org Cc: linux-kernel@vger.kernel.org, Borislav Petkov , Linus Torvalds , Andrew Morton , Mel Gorman , "linux-mm@kvack.org" , Nadav Amit , Rik van Riel , Dave Hansen , Arjan van de Ven , Peter Zijlstra , Andy Lutomirski Subject: [PATCH v3 01/11] x86/mm: Don't reenter flush_tlb_func_common() Date: Tue, 20 Jun 2017 22:22:07 -0700 Message-Id: X-Mailer: git-send-email 2.9.4 In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2874 Lines: 81 It was historically possible to have two concurrent TLB flushes targetting 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. Nadav noticed the reentrancy issue in a different context, but neither of us realized that it caused a problem yet. Cc: Nadav Amit Cc: Dave Hansen Reported-by: "Levin, Alexander (Sasha Levin)" Fixes: 3d28ebceaffa ("x86/mm: Rework lazy TLB to track the actual loaded mm") Signed-off-by: Andy Lutomirski --- 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); -- 2.9.4