Re: [PATCH v1 1/7] selftests/vm: anon_cow: test COW handling of anonymous memory

From: David Hildenbrand <david@redhat.com>
To: Rafael Mendonca <rafaelmendsr@gmail.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-kselftest@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Shuah Khan <shuah@kernel.org>, Jason Gunthorpe <jgg@nvidia.com>,
	John Hubbard <jhubbard@nvidia.com>, Nadav Amit <namit@vmware.com>,
	Peter Xu <peterx@redhat.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Vlastimil Babka <vbabka@suse.cz>, Mike Rapoport <rppt@kernel.org>,
	Christoph von Recklinghausen <crecklin@redhat.com>,
	Don Dutile <ddutile@redhat.com>
Subject: Re: [PATCH v1 1/7] selftests/vm: anon_cow: test COW handling of anonymous memory
Date: Tue, 25 Oct 2022 09:05:34 +0200	[thread overview]
Message-ID: <b9e88ddf-e0ac-ce81-d6b4-caf70772c455@redhat.com> (raw)
In-Reply-To: <Y1bD+8CMzlqkbPwU@macondo>

>> +	/* See if we still read the old values via the pipe. */
>> +	for (total = 0; total < transferred; total += cur) {
>> +		cur = read(fds[0], new + total, transferred - total);
>> +		if (cur < 0)
> 
> Hi David,
> I was looking at some coccinelle reports for linux-next and
> saw the following warning for this comparison:
> 
>    WARNING: Unsigned expression compared with zero: cur < 0
> 
> I think 'cur' needs to be of type 'ssize_t' for this comparison to work.
> 
> The same warning is reported for the variable 'transferred' above, and
> also for do_test_iouring() and do_test_vmsplice_in_parent() in
> "selftests/vm: anon_cow: add liburing test cases".
> 

Thanks for reporting! Indeed, we need a signed value.

-- 
Thanks,

David / dhildenb