From: Tejun Heo <tj@kernel.org>
To: Jan Kara <jack@suse.cz>
Cc: Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH block/for-next] writeback: add tracepoints for cgroup foreign writebacks
Date: Fri, 30 Aug 2019 08:49:21 -0700 [thread overview]
Message-ID: <20190830154921.GZ2263813@devbig004.ftw2.facebook.com> (raw)
In-Reply-To: <20190830154023.GC25069@quack2.suse.cz>
Hello, Jan.
On Fri, Aug 30, 2019 at 05:40:23PM +0200, Jan Kara wrote:
> > + TP_fast_assign(
> > + strncpy(__entry->name, dev_name(wb->bdi->dev), 32);
> > + __entry->bdi_id = wb->bdi->id;
> > + __entry->ino = page->mapping->host->i_ino;
> > + __entry->memcg_id = wb->memcg_css->id;
> > + __entry->cgroup_ino = __trace_wb_assign_cgroup(wb);
> > + __entry->page_cgroup_ino = page->mem_cgroup->css.cgroup->kn->id.ino;
> > + ),
>
> Are the page dereferences above safe? I suppose lock_page_memcg() protects
> the page->mem_cgroup->css.cgroup->kn->id dereference? But page->mapping
> does not seem to be protected by page lock?
Hah, I assumed it would work because there are preceding if
(page_mapping()) tests in the dirty paths -
e.g. __set_page_dirty_nobuffers(). Oh, regardless of that assumption,
I should have used page_mapping().
Thanks.
--
tejun
next prev parent reply other threads:[~2019-08-30 15:49 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-29 22:47 [PATCH block/for-next] writeback: add tracepoints for cgroup foreign writebacks Tejun Heo
2019-08-30 13:43 ` Jens Axboe
2019-08-30 15:40 ` Jan Kara
2019-08-30 15:49 ` Tejun Heo [this message]
2019-08-30 16:42 ` Jan Kara
2019-08-30 17:09 ` Tejun Heo
2019-09-02 8:38 ` Jan Kara
2019-08-30 15:51 ` Tejun Heo
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