linux-kernel - Re: [PATCH 4.18 000/123] 4.18.6-stable review

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Date:   Tue, 4 Sep 2018 19:23:21 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     holger@...lied-asynchrony.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Shuah Khan <shuah@...nel.org>, patches@...nelci.org,
        Ben Hutchings <ben.hutchings@...ethink.co.uk>,
        lkft-triage@...ts.linaro.org, stable <stable@...r.kernel.org>
Subject: Re: [PATCH 4.18 000/123] 4.18.6-stable review

On Tue, Sep 04, 2018 at 10:12:13AM -0700, Linus Torvalds wrote:
> On Mon, Sep 3, 2018 at 11:39 AM Holger Hoffstätte
> <holger@...lied-asynchrony.com> wrote:
> >
> > Sep  3 20:19:38 ragnarok kernel:  tlb_flush_mmu_tlbonly+0x76/0xc0
> > Sep  3 20:19:38 ragnarok kernel:  tlb_table_flush.part.13+0xe/0x30
> > Sep  3 20:19:38 ragnarok kernel:  tlb_flush_mmu_tlbonly+0x54/0xc0
> > ..a few hundred times..
> > Sep  3 20:19:38 ragnarok kernel:  tlb_table_flush.part.13+0xe/0x30
> > Sep  3 20:19:38 ragnarok kernel:  tlb_flush_mmu_tlbonly+0x54/0xc0
> > Sep  3 20:19:38 ragnarok kernel:  arch_tlb_finish_mmu+0x3a/0x70
> > Sep  3 20:19:38 ragnarok kernel:  tlb_finish_mmu+0x1f/0x30
> 
> Yeah, so what seems to have happened is that commit db7ddef30112 ("mm:
> move tlb_table_flush to tlb_flush_mmu_free") wasn't applied to the
> stable tree (because it wasn't an obvious dependency).
> 
> And without that, the backport of d86564a2f085 ("mm/tlb, x86/mm:
> Support invalidating TLB caches for RCU_TABLE_FREE") ends up with
> recursion from tlb_flush_mmu_tlbonly() calling tlb_table_flush(),
> which in turn calls tlb_table_invalidate(), which calls back to
> tlb_flush_mmu_tlbonly().
> 
> So you have endless recursion - at least until you run out of stack.
> Then, if you have VMAP_STACK enabled (x86-64 without KASAN), you get a
> nice clean kernel stack overflow message like you did.
> 
> Or if you have KASAN enabled and no VMAP stack, you just end up with
> random hangs and huge memory corruption as the recursion stomps all
> over your memory.

Ok, I will go queue this patch up now, it was in my very-long "to-apply"
queue, but I didn't catch the dependancy here.

thanks,

greg k-h