From: Paolo Bonzini <pbonzini@redhat.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: kvm@vger.kernel.org, "Michael S. Tsirkin" <mst@redhat.com>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org,
David Miller <davem@davemloft.net>
Subject: Re: [PULL 2/2] vhost: replace rcu with mutex
Date: Tue, 03 Jun 2014 16:20:28 +0200 [thread overview]
Message-ID: <538DD9AC.8050606@redhat.com> (raw)
In-Reply-To: <1401803863.3645.208.camel@edumazet-glaptop2.roam.corp.google.com>
Il 03/06/2014 15:57, Eric Dumazet ha scritto:
> On Tue, 2014-06-03 at 14:48 +0200, Paolo Bonzini wrote:
>> Il 02/06/2014 23:58, Eric Dumazet ha scritto:
>>> This looks dubious
>>>
>>> What about using kfree_rcu() instead ?
>>
>> It would lead to unbound allocation from userspace.
>
> Look at how we did this in commit
> c3059477fce2d956a0bb3e04357324780c5d8eeb
That would make VHOST_SET_MEMORY as slow as before (even though once
every few times).
>>> translate_desc() still uses rcu_read_lock(), its not clear if the mutex
>>> is really held.
>>
>> Yes, vhost_get_vq_desc must be called with the vq mutex held.
>>
>> The rcu_read_lock/unlock in translate_desc is unnecessary.
>
> Yep, this is what I pointed out. This is not only necessary, but
> confusing and might be incorrectly copy/pasted in the future.
>
> This patch is a partial one and leaves confusion.
I agree.
Paolo
WARNING: multiple messages have this Message-ID (diff)
From: Paolo Bonzini <pbonzini@redhat.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
netdev@vger.kernel.org,
virtualization@lists.linux-foundation.org,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
David Miller <davem@davemloft.net>
Subject: Re: [PULL 2/2] vhost: replace rcu with mutex
Date: Tue, 03 Jun 2014 16:20:28 +0200 [thread overview]
Message-ID: <538DD9AC.8050606@redhat.com> (raw)
In-Reply-To: <1401803863.3645.208.camel@edumazet-glaptop2.roam.corp.google.com>
Il 03/06/2014 15:57, Eric Dumazet ha scritto:
> On Tue, 2014-06-03 at 14:48 +0200, Paolo Bonzini wrote:
>> Il 02/06/2014 23:58, Eric Dumazet ha scritto:
>>> This looks dubious
>>>
>>> What about using kfree_rcu() instead ?
>>
>> It would lead to unbound allocation from userspace.
>
> Look at how we did this in commit
> c3059477fce2d956a0bb3e04357324780c5d8eeb
That would make VHOST_SET_MEMORY as slow as before (even though once
every few times).
>>> translate_desc() still uses rcu_read_lock(), its not clear if the mutex
>>> is really held.
>>
>> Yes, vhost_get_vq_desc must be called with the vq mutex held.
>>
>> The rcu_read_lock/unlock in translate_desc is unnecessary.
>
> Yep, this is what I pointed out. This is not only necessary, but
> confusing and might be incorrectly copy/pasted in the future.
>
> This patch is a partial one and leaves confusion.
I agree.
Paolo
next prev parent reply other threads:[~2014-06-03 14:20 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-02 21:30 [PULL 0/2] vhost enhancements for 3.16 Michael S. Tsirkin
2014-06-02 21:30 ` Michael S. Tsirkin
2014-06-02 21:30 ` [PULL 1/2] vhost-net: extend device allocation to vmalloc Michael S. Tsirkin
2014-06-02 21:30 ` Michael S. Tsirkin
2014-06-02 21:30 ` [PULL 2/2] vhost: replace rcu with mutex Michael S. Tsirkin
2014-06-02 21:30 ` Michael S. Tsirkin
2014-06-02 21:58 ` Eric Dumazet
2014-06-02 21:58 ` Eric Dumazet
2014-06-03 12:48 ` Paolo Bonzini
2014-06-03 12:48 ` Paolo Bonzini
2014-06-03 13:35 ` Vlad Yasevich
2014-06-03 13:35 ` Vlad Yasevich
2014-06-03 13:55 ` Paolo Bonzini
2014-06-03 13:55 ` Paolo Bonzini
2014-06-03 13:57 ` Eric Dumazet
2014-06-03 13:57 ` Eric Dumazet
2014-06-03 14:20 ` Paolo Bonzini [this message]
2014-06-03 14:20 ` Paolo Bonzini
2014-06-04 19:51 ` Michael S. Tsirkin
2014-06-04 19:51 ` Michael S. Tsirkin
2014-06-05 10:45 ` Michael S. Tsirkin
2014-06-05 10:45 ` Michael S. Tsirkin
2014-06-04 18:12 ` Michael S. Tsirkin
2014-06-04 18:12 ` Michael S. Tsirkin
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