From: Matthew Wilcox <willy@infradead.org>
To: Wei Yongjun <weiyongjun1@huawei.com>
Cc: Pankaj Bharadiya <pankaj.laxminarayan.bharadiya@intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
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 04:14:03 -0700 [thread overview]
Message-ID: <20200428111403.GJ29705@bombadil.infradead.org> (raw)
In-Reply-To: <20200428034736.27850-1-weiyongjun1@huawei.com>
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. This probably confuses all kinds
of automated checkers, and I should probably rewrite the code to not
acquire the new spinlock until we're already holding the xa_lock.
Converting to GFP_ATOMIC is completely wrong.
next prev parent reply other threads:[~2020-04-28 11:14 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-28 3:47 Wei Yongjun
2020-04-28 11:14 ` Matthew Wilcox [this message]
2020-04-29 0:14 ` Andrew Morton
2020-04-29 1:48 ` Matthew Wilcox
2020-04-29 5:22 ` Manfred Spraul
2020-04-29 13:08 ` Matthew Wilcox
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