From mboxrd@z Thu Jan  1 00:00:00 1970
From: Maxime Coquelin <maxime.coquelin@redhat.com>
Subject: Re: [PATCH v2 2/3] vhost: protect dirty logging against
 logging base change
Date: Tue, 28 Nov 2017 11:06:15 +0100
Message-ID: <06080f95-a65a-a449-1c47-72b9d4d53122@redhat.com>
References: <20171124180826.18439-1-maxime.coquelin@redhat.com>
 <20171124180826.18439-3-maxime.coquelin@redhat.com>
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On 11/24/2017 07:08 PM, Maxime Coquelin wrote:
> When performing live-migration with multiple queue pairs,
> VHOST_USER_SET_LOG_BASE request is sent multiple times.
> 
> If packets are being processed by the PMD threads, it is
> possible that they are setting bits in the dirty log map while
> its region is being unmapped by the vhost-user protocol thread.
> It results in the following crash:
> Thread 3 "lcore-slave-2" received signal SIGSEGV, Segmentation fault.
> [Switching to Thread 0x7f71ca495700 (LWP 32451)]
> 0x00000000004bfc8a in vhost_set_bit (addr=0x7f71cbe18432 <error: Cannot access memory at address 0x7f71cbe18432>, nr=1) at /home/max/projects/src/mainline/dpdk/lib/librte_vhost/vhost.h:267
> 267        __sync_fetch_and_or_8(addr, (1U << nr));
> 
> We can see the vhost-user protocol thread just did the unmap of the
> dirty log region when it happens.
> 
> This patch prevents this by introducing a RW lock to protect
> the log base.
> 
> Fixes: 54f9e32305d4 ("vhost: handle dirty pages logging request")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> ---
>   lib/librte_vhost/vhost.c      |  2 ++
>   lib/librte_vhost/vhost.h      | 14 +++++++++++---
>   lib/librte_vhost/vhost_user.c |  4 ++++
>   3 files changed, 17 insertions(+), 3 deletions(-)
> 

By clarifying the vhost-user spec, we may be able to avoid this lock and
just ignore the subsequent SET_LOG_BASE requests once
VHOST_F_LOG_ALL feature bit is set.

So let's just discard this series for now.

Maxime