From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f72.google.com (mail-oi0-f72.google.com [209.85.218.72]) by kanga.kvack.org (Postfix) with ESMTP id 4745F6B02C3 for ; Mon, 19 Jun 2017 23:05:18 -0400 (EDT) Received: by mail-oi0-f72.google.com with SMTP id c189so78295137oia.13 for ; Mon, 19 Jun 2017 20:05:18 -0700 (PDT) Received: from szxga01-in.huawei.com (szxga01-in.huawei.com. [45.249.212.187]) by mx.google.com with ESMTPS id q84si2455388oif.1.2017.06.19.20.05.15 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 19 Jun 2017 20:05:17 -0700 (PDT) Message-ID: <59488EE2.1080403@huawei.com> Date: Tue, 20 Jun 2017 10:56:34 +0800 From: zhong jiang MIME-Version: 1.0 Subject: Re: [PATCH] x86/mm: Don't reenter flush_tlb_func_common() References: <5947D2AE.6080609@huawei.com> In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andy Lutomirski Cc: X86 ML , "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 On 2017/6/19 23:05, Andy Lutomirski wrote: > On Mon, Jun 19, 2017 at 6:33 AM, zhong jiang wrote: >> 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? > Is there a code path that does this? eg: cpu1 cpu2 flush_tlb_page unuse_mm current->mm = NULL current->mm == NULL leave_mm (cpu_tlbstate.state is TLBSATATE_OK) enter_lazy_tlb I am not sure the above race whether exist or not. Do you point out the problem if it is not existence? please Thanks zhongjiang > > Also, the IPI handler on 3.4 looks like this: > > if (f->flush_mm == percpu_read(cpu_tlbstate.active_mm)) { > if (percpu_read(cpu_tlbstate.state) == TLBSTATE_OK) { > if (f->flush_va == TLB_FLUSH_ALL) > local_flush_tlb(); > else > __flush_tlb_one(f->flush_va); > } else > leave_mm(cpu); > } > > but leave_mm() checks the same condition (cpu_tlbstate.state, not > current->mm). How is the BUG triggering? > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email@kvack.org > > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org