linux-kernel - Re: [PATCH v6 18/24] mm: Try spin lock in speculative path

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Message-ID: <20180112181840.GA7590@bombadil.infradead.org>
Date:   Fri, 12 Jan 2018 10:18:40 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Laurent Dufour <ldufour@...ux.vnet.ibm.com>
Cc:     paulmck@...ux.vnet.ibm.com, peterz@...radead.org,
        akpm@...ux-foundation.org, kirill@...temov.name,
        ak@...ux.intel.com, mhocko@...nel.org, dave@...olabs.net,
        jack@...e.cz, benh@...nel.crashing.org, mpe@...erman.id.au,
        paulus@...ba.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, hpa@...or.com,
        Will Deacon <will.deacon@....com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        kemi.wang@...el.com, sergey.senozhatsky.work@...il.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        haren@...ux.vnet.ibm.com, khandual@...ux.vnet.ibm.com,
        npiggin@...il.com, bsingharora@...il.com,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org
Subject: Re: [PATCH v6 18/24] mm: Try spin lock in speculative path

On Fri, Jan 12, 2018 at 06:26:02PM +0100, Laurent Dufour wrote:
> There is a deadlock when a CPU is doing a speculative page fault and
> another one is calling do_unmap().
> 
> The deadlock occurred because the speculative path try to spinlock the
> pte while the interrupt are disabled. When the other CPU in the
> unmap's path has locked the pte then is waiting for all the CPU to
> invalidate the TLB. As the CPU doing the speculative fault have the
> interrupt disable it can't invalidate the TLB, and can't get the lock.
> 
> Since we are in a speculative path, we can race with other mm action.
> So let assume that the lock may not get acquired and fail the
> speculative page fault.

It seems like you introduced this bug in the previous patch, and now
you're fixing it in this patch?  Why not merge the two?