From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
Wei Liu <wei.liu2@citrix.com>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
George Dunlap <George.Dunlap@eu.citrix.com>,
Tim Deegan <tim@xen.org>, Ian Jackson <Ian.Jackson@eu.citrix.com>,
Julien Grall <julien.grall@arm.com>,
xen-devel <xen-devel@lists.xenproject.org>
Subject: Re: [PATCH v2] mm: disallow MEMF_no_refcount to be passed for domain-owned allocations
Date: Fri, 23 Nov 2018 10:50:19 +0000 [thread overview]
Message-ID: <b245229e-ae0d-1b57-d23a-49b1915ccd85@citrix.com> (raw)
In-Reply-To: <5BF7DB2102000078001FF53F@prv1-mh.provo.novell.com>
On 23/11/2018 10:49, Jan Beulich wrote:
>>>> On 23.11.18 at 11:28, <andrew.cooper3@citrix.com> wrote:
>> On 23/11/2018 09:45, Jan Beulich wrote:
>>> When such pages get assigned to domains (and hence their ->tot_pages
>>> not incremented accordingly) we would otherwise also need to suppress
>>> decrementing the count when freeing those pages.
>>>
>>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>>> ---
>>> v2: Add ASSERT_UNREACHABLE().
>>>
>>> --- a/xen/common/page_alloc.c
>>> +++ b/xen/common/page_alloc.c
>>> @@ -2303,6 +2303,11 @@ struct page_info *alloc_domheap_pages(
>>>
>>> if ( memflags & MEMF_no_owner )
>>> memflags |= MEMF_no_refcount;
>>> + else if ( (memflags & MEMF_no_refcount) && d )
>>> + {
>>> + ASSERT_UNREACHABLE();
>> Sorry to do this, but on second thoughts, this path isn't actually
>> unreachable.
>>
>> Could I talk you into using ASSERT(!"Assigned domheap pages must be
>> refcounted") instead, to give a slightly more clear error to developers
>> who manage to hit it?
> I think there are other places where we use ASSERT_UNREACHABLE()
> when the path is reachable in the sense that one could construct a
> suitable path, but with how things are (supposed to be) it cannot be
> reached. I'm unconvinced the added string literal would be of overly
> much help - once you see the line number, it is pretty easy to figure
> out whats wrong.
>
> But if you insist, I'll switch to the alternative way of expressing it
> (although I'd then perhaps use
> ASSERT(!(memflags & MEMF_no_refcount)) instead). Just let me
> know.
That's fine as well.
~Andrew
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next prev parent reply other threads:[~2018-11-23 10:50 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-20 16:12 [PATCH 0/4] XSA-276 follow-up Jan Beulich
2018-11-20 16:17 ` [PATCH 1/4] mm: disallow MEMF_no_refcount to be passed for domain-owned allocations Jan Beulich
2018-11-20 16:35 ` Andrew Cooper
2018-11-23 9:45 ` [PATCH v2] " Jan Beulich
2018-11-23 10:28 ` Andrew Cooper
2018-11-23 10:49 ` Jan Beulich
2018-11-23 10:50 ` Andrew Cooper [this message]
2018-11-20 16:18 ` [PATCH 2/4] x86: correct instances of PGC_allocated clearing Jan Beulich
2018-11-20 16:59 ` Andrew Cooper
2018-11-20 17:12 ` Jan Beulich
2018-11-21 2:47 ` Tamas K Lengyel
2018-11-20 16:19 ` [PATCH 3/4] x86: reduce code duplication in guest_remove_page() Jan Beulich
2018-11-20 17:06 ` Andrew Cooper
2018-11-21 9:28 ` Jan Beulich
2018-11-20 16:19 ` [PATCH 4/4] make domain_adjust_tot_pages() __must_check Jan Beulich
2018-12-05 16:14 ` [PATCH v2 0/2] remaining XSA-276 follow-up Jan Beulich
2018-12-05 16:17 ` [PATCH v2 1/2] x86: reduce code duplication in guest_remove_page() Jan Beulich
2018-12-05 20:03 ` Andrew Cooper
2018-12-05 16:17 ` [PATCH v2 2/2] make domain_adjust_tot_pages() __must_check Jan Beulich
2018-12-05 20:08 ` Andrew Cooper
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