From: Pingfan Liu <kernelfans@gmail.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org,
Valentin Schneider <valentin.schneider@arm.com>,
Peter Zijlstra <peterz@infradead.org>,
Frederic Weisbecker <frederic@kernel.org>,
Baokun Li <libaokun1@huawei.com>,
Mark Rutland <mark.rutland@arm.com>,
Steven Price <steven.price@arm.com>,
"Jason A. Donenfeld" <Jason@zx2c4.com>,
Yuan ZhaoXiong <yuanzhaoxiong@baidu.com>,
YueHaibing <yuehaibing@huawei.com>,
Randy Dunlap <rdunlap@infradead.org>
Subject: Re: [PATCH 7/9] irq: remove needless lock in takedown_cpu()
Date: Mon, 25 Apr 2022 10:57:05 +0800 [thread overview]
Message-ID: <YmYOAfz3Oh1bYiVi@piliu.users.ipa.redhat.com> (raw)
In-Reply-To: <87y1zys9f7.ffs@tglx>
On Thu, Apr 21, 2022 at 06:11:56PM +0200, Thomas Gleixner wrote:
> On Wed, Apr 20 2022 at 22:05, Pingfan Liu wrote:
>
> First of all, the subject prefix for the core interrupt subsystem is
> 'genirq' and the sentence after the colon starts with an uppercase
> letter. See:
>
> https://www.kernel.org/doc/html/latest/process/maintainer-tip.html
>
> > diff --git a/kernel/cpu.c b/kernel/cpu.c
> > index d0a9aa0b42e8..94a6b512c26d 100644
> > --- a/kernel/cpu.c
> > +++ b/kernel/cpu.c
> > @@ -1033,18 +1033,16 @@ static int takedown_cpu(unsigned int cpu)
> > kthread_park(st->thread);
> >
> > /*
> > - * Prevent irq alloc/free while the dying cpu reorganizes the
> > - * interrupt affinities.
> > + * RCU keeps watching 'cpu' until do_idle()->rcu_report_dead().
> > + * And cpu_stopper's fn is dispatched with preemption disabled.
> > + * So it can not occur to release a irq_desc.
> > */
> > - irq_lock_sparse();
>
> Not everything is about RCU here. You really need to look at all moving
> parts:
>
> irq_migrate_all_off_this_cpu() relies on the allocated_irqs bitmap and
> the sparse tree to be in consistent state, which is only guaranteed when
> the sparse lock is held.
>
For the irq which transfer from active to inactive(disappearing) after
fetching, desc->lock can serve the sync purpose. In this case,
irq_lock_sparse() is not needed. For a emergeing irq, I am not sure
about it.
> I'm not sure what you are trying to solve here. Not taking sparse_irq_lock
> here is not gaining anything.
>
It was a big lock preventing my original series to make kexec-reboot parallel on
arm64/riscv platform. But my new series takes a different way. And this
big lock is not a problem any longer.
Thanks for your time.
Regards,
Pingfan
next prev parent reply other threads:[~2022-04-25 2:57 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-20 14:05 [PATCH 0/9] trival fix or improvement about irq_desc access Pingfan Liu
2022-04-20 14:05 ` [PATCH 1/9] irq/irqdesc: put the lock at the exact place in irq_sysfs_init() Pingfan Liu
2022-04-20 14:05 ` [PATCH 2/9] irq/irqdesc: change the name of delete_irq_desc() to irq_delete_desc() Pingfan Liu
2022-04-20 14:05 ` [PATCH 3/9] irq/manage: remove some unreferenced code Pingfan Liu
2022-04-20 20:56 ` Miguel Ojeda
2022-04-20 14:05 ` [PATCH 4/9] s390/irq: utilize RCU instead of irq_lock_sparse() in show_msi_interrupt() Pingfan Liu
2022-04-20 18:16 ` Heiko Carstens
2022-04-21 3:36 ` Pingfan Liu
2022-04-21 11:42 ` Heiko Carstens
2022-04-22 9:56 ` Pingfan Liu
2022-04-22 10:02 ` [PATCHv2] " Pingfan Liu
2022-04-25 11:39 ` Heiko Carstens
2022-04-20 14:05 ` [PATCH 5/9] x86/irq: place for_each_active_irq() in rcu read section Pingfan Liu
2022-04-20 14:05 ` [PATCH 6/9] pm/irq: make for_each_irq_desc() safe of irq_desc release Pingfan Liu
2022-04-20 16:23 ` Rafael J. Wysocki
2022-04-21 3:31 ` Pingfan Liu
2022-04-21 10:57 ` Rafael J. Wysocki
2022-04-22 10:43 ` Pingfan Liu
2022-04-27 6:03 ` [PATCHv2] genirq/PM: Make " Pingfan Liu
2022-04-20 14:05 ` [PATCH 7/9] irq: remove needless lock in takedown_cpu() Pingfan Liu
2022-04-21 16:11 ` Thomas Gleixner
2022-04-25 2:57 ` Pingfan Liu [this message]
2022-04-25 9:43 ` Thomas Gleixner
2022-04-27 6:01 ` Pingfan Liu
2022-04-20 14:05 ` [PATCH 8/9] irq: make irq_lock_sparse() independent of CONFIG_SPARSE_IRQ Pingfan Liu
2022-04-20 14:05 ` [PATCH 9/9] irq/irqdesc: rename sparse_irq_lock to bitmap_lock Pingfan Liu
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=YmYOAfz3Oh1bYiVi@piliu.users.ipa.redhat.com \
--to=kernelfans@gmail.com \
--cc=Jason@zx2c4.com \
--cc=frederic@kernel.org \
--cc=libaokun1@huawei.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mark.rutland@arm.com \
--cc=peterz@infradead.org \
--cc=rdunlap@infradead.org \
--cc=steven.price@arm.com \
--cc=tglx@linutronix.de \
--cc=valentin.schneider@arm.com \
--cc=yuanzhaoxiong@baidu.com \
--cc=yuehaibing@huawei.com \
/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;
as well as URLs for NNTP newsgroup(s).