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From: Andrew Morton <akpm@linux-foundation.org>
To: Matthew Wilcox <willy@infradead.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 17:14:20 -0700	[thread overview]
Message-ID: <20200428171420.045f0acc9e1bf20044c4560e@linux-foundation.org> (raw)
In-Reply-To: <20200428111403.GJ29705@bombadil.infradead.org>

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?

>  This probably confuses all kinds
> of automated checkers,

A big fat code comment would reduce the email traffic?

> and I should probably rewrite the code to not
> acquire the new spinlock until we're already holding the xa_lock.
> 


WARNING: multiple messages have this Message-ID (diff)
From: Andrew Morton <akpm@linux-foundation.org>
To: Matthew Wilcox <willy@infradead.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: Wed, 29 Apr 2020 00:14:20 +0000	[thread overview]
Message-ID: <20200428171420.045f0acc9e1bf20044c4560e@linux-foundation.org> (raw)
In-Reply-To: <20200428111403.GJ29705@bombadil.infradead.org>

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?

>  This probably confuses all kinds
> of automated checkers,

A big fat code comment would reduce the email traffic?

> and I should probably rewrite the code to not
> acquire the new spinlock until we're already holding the xa_lock.
> 

  reply	other threads:[~2020-04-29  0:14 UTC|newest]

Thread overview: 12+ 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  3:47 ` Wei Yongjun
2020-04-28 11:14 ` Matthew Wilcox
2020-04-28 11:14   ` Matthew Wilcox
2020-04-29  0:14   ` Andrew Morton [this message]
2020-04-29  0:14     ` Andrew Morton
2020-04-29  1:48     ` Matthew Wilcox
2020-04-29  1:48       ` Matthew Wilcox
2020-04-29  5:22   ` Manfred Spraul
2020-04-29  5:22     ` Manfred Spraul
2020-04-29 13:08     ` Matthew Wilcox
2020-04-29 13:08       ` Matthew Wilcox

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