From: Aristeu Rozanski <aris@ruivo.org>
To: David Hildenbrand <david@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>,
linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
Maxime Ripard <mripard@kernel.org>,
Thomas Zimmermann <tzimmermann@suse.de>,
David Airlie <airlied@gmail.com>, Simona Vetter <simona@ffwll.ch>
Subject: Re: [PATCH] mm: make folio page count functions return unsigned
Date: Tue, 26 Aug 2025 18:00:41 -0400 [thread overview]
Message-ID: <20250826220041.GS3581799@cathedrallabs.org> (raw)
In-Reply-To: <a959a7f8-20c0-4c2a-9cef-ffad4f8b805b@redhat.com>
On Tue, Aug 26, 2025 at 11:45:52PM +0200, David Hildenbrand wrote:
> IIRC, the issue is if we pass -folio_nr_pages() to functions that expect
> a "long" and we are using "unsigned int" as return type.
some actually expect an int (e.g. memcg1_charge_statistics()), it'd be a good
idea to get those fixed.
> Then, e.g., -1 will be (unsigned int)0xffffffff, and casting that to
> "long" means trouble, because we wouldn't sign-extend properly and get
> (long)0x00000000ffffffff.
>
> Using "unsigned long" instead work perfectly fine.
>
> e.g., -1 will be (unsigned long)0xffffffffffffffff. Passing that to a
> function that expects "long" or "unsigned long" works as expected.
We could run into problems if folio_nr_pages() ever returns an unsigned long
larger than LONG_MAX :^)
--
Aristeu
next prev parent reply other threads:[~2025-08-26 22:01 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-08-26 15:37 Aristeu Rozanski
2025-08-26 19:00 ` Matthew Wilcox
2025-08-26 21:45 ` David Hildenbrand
2025-08-26 22:00 ` Aristeu Rozanski [this message]
2025-08-27 1:20 ` Matthew Wilcox
2025-08-27 9:14 ` David Hildenbrand
2025-08-27 9:13 ` David Hildenbrand
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