From: Linus Torvalds <torvalds@linux-foundation.org>
To: Vernon Yang <vernon2gm@gmail.com>
Cc: tytso@mit.edu, Jason@zx2c4.com, davem@davemloft.net,
edumazet@google.com, kuba@kernel.org, pabeni@redhat.com,
jejb@linux.ibm.com, martin.petersen@oracle.com,
yury.norov@gmail.com, andriy.shevchenko@linux.intel.com,
linux@rasmusvillemoes.dk, james.smart@broadcom.com,
dick.kennedy@broadcom.com, linux-kernel@vger.kernel.org,
wireguard@lists.zx2c4.com, netdev@vger.kernel.org,
linux-scsi@vger.kernel.org
Subject: Re: [PATCH 5/5] cpumask: fix comment of cpumask_xxx
Date: Mon, 6 Mar 2023 09:47:34 -0800 [thread overview]
Message-ID: <CAHk-=witXXeQuP9fgs4dDL2Ex0meXQiHJs+3JEfNdaPwngMVEg@mail.gmail.com> (raw)
In-Reply-To: <CAHk-=whVnaTBt2Xm-A+8SMc5-q5CuZBDU6rUZ8yC8GoAnbTBvw@mail.gmail.com>
On Mon, Mar 6, 2023 at 9:29 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> The correct thing to do is always that
>
> * Returns >= nr_cpu_ids if no cpus set.
>
> because nr_cpu_ids is always the *smallest* of the access sizes.
>
> Of course, right now Guenter seems to be reporting a problem with that
> optimization, so unless I figure out what is going on I'll just need
> to revert it anyway.
Ahh. And the reason is exactly that people do *not* follow that
"Returns >= nr_cpu_ids" rule.
The drivers/char/random.c code is very wrong, and does
if (cpu == nr_cpumask_bits)
cpu = cpumask_first(&timer_cpus);
which fails miserably exactly because it doesn't use ">=".
Oh well.
I'll have to look for more of this pattern, but basically all those
"xyz_cpumask_bits" things were supposed to always be just internal to
that header file implementation, which is *exactly* why you have to
check the result for ">= nr_cpu_ids".
Linus
next prev parent reply other threads:[~2023-03-06 17:47 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-06 16:06 [PATCH 0/5] fix call cpumask_next() if no further cpus set Vernon Yang
2023-03-06 16:06 ` [PATCH 1/5] random: fix try_to_generate_entropy() " Vernon Yang
2023-03-06 16:26 ` Yury Norov
2023-03-06 16:06 ` [PATCH 2/5] wireguard: fix wg_cpumask_choose_online() " Vernon Yang
2023-03-06 16:06 ` [PATCH 3/5] scsi: lpfc: fix lpfc_cpu_affinity_check() " Vernon Yang
2023-03-06 18:48 ` Linus Torvalds
2023-03-06 20:09 ` Vernon Yang
2023-03-06 16:06 ` [PATCH 4/5] scsi: lpfc: fix lpfc_nvmet_setup_io_context() " Vernon Yang
2023-03-06 16:06 ` [PATCH 5/5] cpumask: fix comment of cpumask_xxx Vernon Yang
2023-03-06 16:39 ` Yury Norov
2023-03-06 16:44 ` Jason A. Donenfeld
2023-03-06 16:54 ` Yury Norov
2023-03-06 17:04 ` Jason A. Donenfeld
2023-03-06 17:45 ` Vernon Yang
2023-03-06 17:29 ` Linus Torvalds
2023-03-06 17:47 ` Linus Torvalds [this message]
2023-03-06 18:02 ` Linus Torvalds
2023-03-06 18:13 ` Vernon Yang
2023-03-06 18:34 ` Linus Torvalds
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