From: Matthew Wilcox <willy@infradead.org>
To: "Pankaj Raghav (Samsung)" <kernel@pankajraghav.com>
Cc: Shuah Khan <shuah@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
gost.dev@samsung.com, mcgrof@kernel.org,
linux-kselftest@vger.kernel.org, Zi Yan <zi.yan@sent.com>,
Pankaj Raghav <p.raghav@samsung.com>
Subject: Re: [PATCH] selftests/mm: use volatile keyword to not optimize mmap read variable
Date: Thu, 6 Jun 2024 15:35:31 +0100 [thread overview]
Message-ID: <ZmHJMyo37QdtTWee@casper.infradead.org> (raw)
In-Reply-To: <20240606135835.600022-1-kernel@pankajraghav.com>
On Thu, Jun 06, 2024 at 01:58:35PM +0000, Pankaj Raghav (Samsung) wrote:
> +++ b/tools/testing/selftests/mm/split_huge_page_test.c
> @@ -300,7 +300,7 @@ int create_pagecache_thp_and_fd(const char *testfile, size_t fd_size, int *fd,
> char **addr)
> {
> size_t i;
> - int __attribute__((unused)) dummy = 0;
> + volatile int __attribute__((unused)) dummy = 0;
The mistake made by whoever wrote this test was making 'dummy' a stack
variable. That lets the compiler figure out that it's unused. If you
make it a top-level variable (not static) so the compiler can't tell
whether it's referenced by a different compilation unit, it can't make
that deduction. And you don't need the stupid attibute or volatile on it.
next prev parent reply other threads:[~2024-06-06 14:35 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-06-06 13:58 Pankaj Raghav (Samsung)
2024-06-06 14:21 ` Zi Yan
2024-06-06 14:35 ` Matthew Wilcox [this message]
2024-06-06 15:19 ` Zi Yan
2024-06-06 15:28 ` Pankaj Raghav (Samsung)
2024-06-06 15:56 ` David Hildenbrand
2024-06-06 15:57 ` David Hildenbrand
2024-06-06 20:18 ` Pankaj Raghav (Samsung)
2024-06-06 20:21 ` David Hildenbrand
2024-06-06 20:30 ` Pankaj Raghav (Samsung)
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