From: Matthew Wilcox <willy@infradead.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Wei Yongjun <weiyongjun1@huawei.com>,
Pankaj Bharadiya <pankaj.laxminarayan.bharadiya@intel.com>,
Waiman Long <longman@redhat.com>,
Manfred Spraul <manfred@colorfullife.com>,
Stephen Rothwell <sfr@canb.auug.org.au>,
Alexey Dobriyan <adobriyan@gmail.com>,
linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org
Subject: Re: [PATCH -next] ipc: use GFP_ATOMIC under spin lock
Date: Tue, 28 Apr 2020 18:48:03 -0700 [thread overview]
Message-ID: <20200429014803.GO29705@bombadil.infradead.org> (raw)
In-Reply-To: <20200428171420.045f0acc9e1bf20044c4560e@linux-foundation.org>
On Tue, Apr 28, 2020 at 05:14:20PM -0700, Andrew Morton wrote:
> On Tue, 28 Apr 2020 04:14:03 -0700 Matthew Wilcox <willy@infradead.org> wrote:
>
> > On Tue, Apr 28, 2020 at 03:47:36AM +0000, Wei Yongjun wrote:
> > > The function ipc_id_alloc() is called from ipc_addid(), in which
> > > a spin lock is held, so we should use GFP_ATOMIC instead.
> > >
> > > Fixes: de5738d1c364 ("ipc: convert ipcs_idr to XArray")
> > > Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
> >
> > I see why you think that, but it's not true. Yes, we hold a spinlock, but
> > the spinlock is in an object which is not reachable from any other CPU.
> > So it's not possible to deadlock.
>
> um, then why are we taking it?
The lock has to be held by the time 'new' is findable because 'new' is
not completely constructed at that point. The finder will try to acquire
the spinlock before looking at the uninitialised fields, so it's safe.
But it's not a common idiom we use at all.
> > This probably confuses all kinds
> > of automated checkers,
>
> A big fat code comment would reduce the email traffic?
I think I can rewrite this to take the spinlock after doing the allocation.
next prev parent reply other threads:[~2020-04-29 1:48 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-28 3:47 [PATCH -next] ipc: use GFP_ATOMIC under spin lock Wei Yongjun
2020-04-28 11:14 ` Matthew Wilcox
2020-04-29 0:14 ` Andrew Morton
2020-04-29 1:48 ` Matthew Wilcox [this message]
2020-04-29 5:22 ` Manfred Spraul
2020-04-29 13:08 ` Matthew Wilcox
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=20200429014803.GO29705@bombadil.infradead.org \
--to=willy@infradead.org \
--cc=adobriyan@gmail.com \
--cc=akpm@linux-foundation.org \
--cc=kernel-janitors@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=longman@redhat.com \
--cc=manfred@colorfullife.com \
--cc=pankaj.laxminarayan.bharadiya@intel.com \
--cc=sfr@canb.auug.org.au \
--cc=weiyongjun1@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).