From: Jason Gunthorpe <jgg@nvidia.com>
To: Yury Norov <ynorov@nvidia.com>
Cc: Yury Norov <yury.norov@gmail.com>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
Eric Biggers <ebiggers@kernel.org>,
"Jason A. Donenfeld" <Jason@zx2c4.com>,
Ard Biesheuvel <ardb@kernel.org>,
linux-kernel@vger.kernel.org, kexec@lists.infradead.org,
linux-cifs@vger.kernel.org, linux-spi@vger.kernel.org,
linux-hyperv@vger.kernel.org,
"K. Y. Srinivasan" <kys@microsoft.com>,
Haiyang Zhang <haiyangz@microsoft.com>,
Leon Romanovsky <leon@kernel.org>,
Mark Brown <broonie@kernel.org>, Steve French <sfrench@samba.org>,
Alexander Graf <graf@amazon.com>, Mike Rapoport <rppt@kernel.org>,
Pasha Tatashin <pasha.tatashin@soleen.com>
Subject: Re: [PATCH] lib: count_zeros: fix 32/64-bit inconsistency in count_trailing_zeros()
Date: Fri, 13 Mar 2026 14:18:55 -0300 [thread overview]
Message-ID: <20260313171855.GA1744604@nvidia.com> (raw)
In-Reply-To: <20260312230817.372878-1-ynorov@nvidia.com>
On Thu, Mar 12, 2026 at 07:08:16PM -0400, Yury Norov wrote:
> Based on 'sizeof(x) == 4' condition, in 32-bit case the function is wired
> to ffs(), while in 64-bit case to __ffs(). The difference is substantial:
> ffs(x) == __ffs(x) + 1. Also, ffs(0) == 0, while __ffs(0) is undefined.
>
> The 32-bit behaviour is inconsistent with the function description, so it
> needs to get fixed.
>
> There are 9 individual users for the function in 6 different subsystems.
> Some arches and drivers are 64-bit only:
> - arch/loongarch/kvm/intc/eiointc.c;
> - drivers/hv/mshv_vtl_main.c;
> - kernel/liveupdate/kexec_handover.c;
>
> The others are:
> - ib_umem_find_best_pgsz(): as per comment, __ffs() should be correct;
So long as 32 bit works the same as 64 bit it is correct for ib
Jason
next prev parent reply other threads:[~2026-03-13 17:19 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-12 23:08 [PATCH] lib: count_zeros: fix 32/64-bit inconsistency in count_trailing_zeros() Yury Norov
2026-03-12 23:54 ` Enzo Matsumiya
2026-03-13 16:31 ` Yury Norov
2026-03-13 9:47 ` Andy Shevchenko
2026-03-13 17:48 ` Yury Norov
2026-03-13 18:41 ` Konstantin Ryabitsev
2026-03-13 17:18 ` Jason Gunthorpe [this message]
2026-03-13 18:14 ` Yury Norov
2026-03-17 9:14 ` Leon Romanovsky
2026-03-18 16:31 ` Yury Norov
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