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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Ankit Khushwaha Subject: Re: [PATCH] mm/selftests: Fix -Wtautological-compare warning in mremap_test.c Message-Id: <20251110100914.af77cb0a5b4211313dd9f32a@linux-foundation.org> In-Reply-To: <20251110175155.1314757-1-wakel@google.com> References: <20251110175155.1314757-1-wakel@google.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 37A5618000F X-Stat-Signature: tg8kw7dsmeje6f9j69wuju3hcsortw1d X-Rspam-User: X-HE-Tag: 1762798156-953026 X-HE-Meta: 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 Tv7TLzQc VWf0UYuZIjSn8awhSRJvVGtAnTmqT1He2iHIyyq56qLMv+5d87rEXDp0W5aVly+WPuqOPc/SIAGpnreIdg/LYX7R7+WzQk+bxOtEGUMTNfjO7X3f6Niltm782hrooKoEOg0HV9IkNl1mI7W5N655zFBvejfS9bX/H35RcdmUkto4zQAFgAutnie3LdtbnFmtrgm5YsjlM+PXl8KyWauxC1hy3CPdwzDVvsmG6p94a+d/6+FFAGBxJ0shbq3dnGxD4U5YiVYPbuYY3AfcP+0L7Vi6GoM+j16IHXSEXxzncXkrR5ybZgQgZudvV40XgBmcdemiQX1r5jNJ+Y4CH7fKYbuz/V/gUin8qg3IKNrBJ+4W29Y+rudExTHPtYqPN8ZGRmyu1n3Wjn8Vj3enHFHXokjnV0a9EKSC1x/i8ssS0DnlD95hOJLFvABUeCROUOEUydbdQ X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 11 Nov 2025 01:51:55 +0800 Wake Liu wrote: > The compiler warns about a tautological comparison in mremap_test.c: > "pointer comparison always evaluates to false [-Wtautological-compare]" > > This occurs when checking for unsigned overflow: > if (addr + c.dest_alignment < addr) > > Cast 'addr' to 'unsigned long long' to ensure the comparison is performed > with a wider type, correctly detecting potential overflow and resolving > the warning. > Thanks. I recently merged https://lore.kernel.org/all/20251108161829.25105-1-ankitkhushwaha.linux@gmail.com/T/#u there has been some discussion... > --- a/tools/testing/selftests/mm/mremap_test.c > +++ b/tools/testing/selftests/mm/mremap_test.c > @@ -1032,7 +1032,7 @@ static long long remap_region(struct config c, unsigned int threshold_mb, > /* Don't destroy existing mappings unless expected to overlap */ > while (!is_remap_region_valid(addr, c.region_size) && !c.overlapping) { > /* Check for unsigned overflow */ > - if (addr + c.dest_alignment < addr) { > + if ((unsigned long long)addr + c.dest_alignment < (unsigned long long)addr) { > ksft_print_msg("Couldn't find a valid region to remap to\n"); > ret = -1; > goto clean_up_src; I wonder if we'd be better off borrowing ideas from include/linux/overflow.h:check_add_overflow(). Did anyone try __builtin_add_overflow() here?