From: "Eric W. Biederman" <ebiederm@xmission.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Maria Yu <quic_aiquny@quicinc.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 12:27:05 -0600 [thread overview]
Message-ID: <87o7eu7ybq.fsf@email.froward.int.ebiederm.org> (raw)
In-Reply-To: <ZXnaNSrtaWbS2ivU@casper.infradead.org> (Matthew Wilcox's message of "Wed, 13 Dec 2023 16:22:13 +0000")
Matthew Wilcox <willy@infradead.org> writes:
> 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.
Yes. It seems to make sense to distinguish between write_lock_irq and
write_lock_irqsave and fix this for all of write_lock_irq.
Either that or someone can put in the work to start making the
tasklist_lock go away.
Eric
next prev parent reply other threads:[~2023-12-13 18:27 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-13 10:17 Maria Yu
2023-12-13 16:22 ` Matthew Wilcox
2023-12-13 18:27 ` Eric W. Biederman [this message]
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
2023-12-25 8:19 Maria Yu
2023-12-25 8:26 ` Aiqun Yu (Maria)
2024-01-03 14:04 ` Jarkko Sakkinen
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87o7eu7ybq.fsf@email.froward.int.ebiederm.org \
--to=ebiederm@xmission.com \
--cc=brauner@kernel.org \
--cc=dhowells@redhat.com \
--cc=jarkko@kernel.org \
--cc=jmorris@namei.org \
--cc=keescook@chromium.or \
--cc=kernel@quicinc.com \
--cc=keyrings@vger.kernel.org \
--cc=linux-arm-msm@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-security-module@vger.kernel.org \
--cc=oleg@redhat.com \
--cc=paul@paul-moore.com \
--cc=quic_aiquny@quicinc.com \
--cc=quic_pkondeti@quicinc.com \
--cc=serge@hallyn.com \
--cc=viro@zeniv.linux.org.uk \
--cc=willy@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox