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From: John Hubbard <jhubbard@nvidia.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
	"Al Viro" <viro@zeniv.linux.org.uk>,
	"Christoph Hellwig" <hch@infradead.org>,
	"Dan Williams" <dan.j.williams@intel.com>,
	"Dave Chinner" <david@fromorbit.com>,
	"Ira Weiny" <ira.weiny@intel.com>, "Jan Kara" <jack@suse.cz>,
	"Jason Gunthorpe" <jgg@ziepe.ca>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Jérôme Glisse" <jglisse@redhat.com>,
	"Michal Hocko" <mhocko@suse.com>,
	"Mike Kravetz" <mike.kravetz@oracle.com>,
	"Shuah Khan" <shuah@kernel.org>,
	"Vlastimil Babka" <vbabka@suse.cz>,
	linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-kselftest@vger.kernel.org, linux-rdma@vger.kernel.org,
	linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH v2 4/8] mm/gup: track FOLL_PIN pages
Date: Thu, 30 Jan 2020 19:19:30 -0800
Message-ID: <1037b514-30e7-c128-38c1-9c98488be337@nvidia.com> (raw)
In-Reply-To: <20200130113126.5ftq4gd5k7o7tipj@box>

On 1/30/20 3:31 AM, Kirill A. Shutemov wrote:
...
>>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>>>> index 0a55dec68925..b1079aaa6f24 100644
>>>> --- a/mm/huge_memory.c
>>>> +++ b/mm/huge_memory.c
>>>> @@ -958,6 +958,11 @@ struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
>>>>   	 */
>>>>   	WARN_ONCE(flags & FOLL_COW, "mm: In follow_devmap_pmd with FOLL_COW set");
>>>> +	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
>>>> +	if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
>>>> +			 (FOLL_PIN | FOLL_GET)))
>>>
>>> Too many parentheses.
>>
>>
>> OK, I'll remove at least one. :)
> 
> I see two.

ah, correction: actually, the original statement has exactly the right number of parentheses.
The relevant C precedence order is:
	==
	&
	|

...which means that both "&" and "|" operations need parentheses protection from the higher
precedence "==" operation.

(There are other places in the kernel that have this exact pattern, too, with the same
pattern of parentheses that I'm using, of course.)

thanks,
-- 
John Hubbard
NVIDIA
 

  reply index

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-29  3:24 [PATCH v2 0/8] mm/gup: track FOLL_PIN pages (follow on from v12) John Hubbard
2020-01-29  3:24 ` [PATCH v2 1/8] mm: dump_page: print head page's refcount, for compound pages John Hubbard
2020-01-29 11:25   ` Kirill A. Shutemov
2020-01-29 22:26     ` John Hubbard
2020-01-29 22:59       ` Matthew Wilcox
2020-01-30  6:23         ` John Hubbard
2020-01-30  6:30           ` John Hubbard
2020-01-29  3:24 ` [PATCH v2 2/8] mm/gup: split get_user_pages_remote() into two routines John Hubbard
2020-01-29  3:24 ` [PATCH v2 3/8] mm/gup: pass a flags arg to __gup_device_* functions John Hubbard
2020-01-29  3:24 ` [PATCH v2 4/8] mm/gup: track FOLL_PIN pages John Hubbard
2020-01-29 13:51   ` Kirill A. Shutemov
2020-01-30  6:44     ` John Hubbard
2020-01-30 11:31       ` Kirill A. Shutemov
2020-01-31  3:19         ` John Hubbard [this message]
2020-01-29  3:24 ` [PATCH v2 5/8] mm/gup: page->hpage_pinned_refcount: exact pin counts for huge pages John Hubbard
2020-01-29  3:24 ` [PATCH v2 6/8] mm/gup: /proc/vmstat: pin_user_pages (FOLL_PIN) reporting John Hubbard
2020-01-29  3:24 ` [PATCH v2 7/8] mm/gup_benchmark: support pin_user_pages() and related calls John Hubbard
2020-01-29  3:24 ` [PATCH v2 8/8] selftests/vm: run_vmtests: invoke gup_benchmark with basic FOLL_PIN coverage John Hubbard

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