From: Matthew Wilcox <willy@infradead.org>
To: Maria Yu <quic_aiquny@quicinc.com>
Cc: ebiederm@xmission.com, kernel@quicinc.com,
quic_pkondeti@quicinc.com, keescook@chromium.or,
viro@zeniv.linux.org.uk, brauner@kernel.org, oleg@redhat.com,
dhowells@redhat.com, jarkko@kernel.org, paul@paul-moore.com,
jmorris@namei.org, serge@hallyn.com, linux-mm@kvack.org,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
keyrings@vger.kernel.org, linux-security-module@vger.kernel.org,
linux-arm-msm@vger.kernel.org
Subject: Re: [PATCH] kernel: Introduce a write lock/unlock wrapper for tasklist_lock
Date: Wed, 13 Dec 2023 16:22:13 +0000 [thread overview]
Message-ID: <ZXnaNSrtaWbS2ivU@casper.infradead.org> (raw)
In-Reply-To: <20231213101745.4526-1-quic_aiquny@quicinc.com>
On Wed, Dec 13, 2023 at 06:17:45PM +0800, Maria Yu wrote:
> +static inline void write_lock_tasklist_lock(void)
> +{
> + while (1) {
> + local_irq_disable();
> + if (write_trylock(&tasklist_lock))
> + break;
> + local_irq_enable();
> + cpu_relax();
This is a bad implementation though. You don't set the _QW_WAITING flag
so readers don't know that there's a pending writer. Also, I've seen
cpu_relax() pessimise CPU behaviour; putting it into a low-power mode
that takes a while to wake up from.
I think the right way to fix this is to pass a boolean flag to
queued_write_lock_slowpath() to let it know whether it can re-enable
interrupts while checking whether _QW_WAITING is set.
next prev parent reply other threads:[~2023-12-13 16:22 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-13 10:17 [PATCH] kernel: Introduce a write lock/unlock wrapper for tasklist_lock Maria Yu
2023-12-13 16:22 ` Matthew Wilcox [this message]
2023-12-13 18:27 ` Eric W. Biederman
2023-12-15 5:52 ` Aiqun Yu (Maria)
2023-12-28 22:20 ` Matthew Wilcox
2023-12-29 11:35 ` kernel test robot
2024-01-02 2:19 ` Aiqun Yu (Maria)
2024-01-02 9:14 ` Matthew Wilcox
2024-01-03 2:58 ` Aiqun Yu (Maria)
2024-01-03 18:18 ` Matthew Wilcox
2024-01-04 0:46 ` Aiqun Yu (Maria)
2024-01-03 6:03 ` kernel test robot
-- strict thread matches above, loose matches on Subject: below --
2023-12-25 8:19 Maria Yu
2023-12-25 8:26 ` Aiqun Yu (Maria)
2024-01-03 14:04 ` Jarkko Sakkinen
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