From: Wei Liu <wei.liu@kernel.org>
To: Michael Kelley <mikelley@microsoft.com>
Cc: "Long Li" <longli@microsoft.com>, "Wei Liu" <wei.liu@kernel.org>,
"longli@linuxonhyperv.com" <longli@linuxonhyperv.com>,
"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
"KY Srinivasan" <kys@microsoft.com>,
"Haiyang Zhang" <haiyangz@microsoft.com>,
"Stephen Hemminger" <sthemmin@microsoft.com>,
"Dexuan Cui" <decui@microsoft.com>,
"Lorenzo Pieralisi" <lorenzo.pieralisi@arm.com>,
"Rob Herring" <robh@kernel.org>,
"Krzysztof Wilczyński" <kw@linux.com>,
"Bjorn Helgaas" <bhelgaas@google.com>,
"Dan Carpenter" <dan.carpenter@oracle.com>
Subject: Re: [PATCH] PCI: hv: Fix a bug on removing child devices on the bus
Date: Thu, 26 Aug 2021 19:41:13 +0000 [thread overview]
Message-ID: <20210826194113.yihk7ete4n4ej4gz@liuwe-devbox-debian-v2> (raw)
In-Reply-To: <MWHPR21MB1593E4B1051F96DB6E715C0CD7C79@MWHPR21MB1593.namprd21.prod.outlook.com>
On Thu, Aug 26, 2021 at 04:50:28PM +0000, Michael Kelley wrote:
> From: Long Li <longli@microsoft.com> Sent: Wednesday, August 25, 2021 1:25 PM
>
> > >
> > > I thought list_for_each_entry_safe() is for use when list manipulation is *not*
> > > protected by a lock and you want to safely walk the list even if an entry gets
> > > removed. If the list is protected by a lock or not subject to contention (as is the
> > > case here), then
> > > list_for_each_entry() is the simpler implementation. The original
> > > implementation didn't need to use the _safe version because of the spin lock.
> > >
> > > Or do I have it backwards?
> > >
> > > Michael
> >
> > I think we need list_for_each_entry_safe() because we delete the list elements while going through them:
> >
> > Here is the comment on list_for_each_entry_safe():
> > /**
> > * Loop through the list, keeping a backup pointer to the element. This
> > * macro allows for the deletion of a list element while looping through the
> > * list.
> > *
> > * See list_for_each_entry for more details.
> > */
> >
>
> Got it. Thanks (and to Rob Herring). I read that comment but
> with the wrong assumptions and didn't understand it correctly.
>
> Interestingly, pci-hyperv.c has another case of looping through
> this list and removing items where the _safe version is not used.
> See pci_devices_present_work() where the missing children are
> moved to a list on the stack.
That can be converted too, I think.
The original code is not wrong per-se. It is just not as concise as
using list_for_each_entry_safe.
Wei.
>
> Michael
next prev parent reply other threads:[~2021-08-26 19:41 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-24 7:20 [PATCH] PCI: hv: Fix a bug on removing child devices on the bus longli
2021-08-24 11:02 ` Wei Liu
2021-08-24 17:28 ` Long Li
2021-08-25 19:11 ` Michael Kelley
2021-08-25 20:25 ` Long Li
2021-08-26 16:50 ` Michael Kelley
2021-08-26 19:41 ` Wei Liu [this message]
2021-08-26 20:09 ` Long Li
2021-08-26 20:15 ` Wei Liu
2021-08-26 20:20 ` Long Li
2021-08-25 20:32 ` Rob Herring
2021-08-24 12:25 ` Bjorn Helgaas
2021-08-24 17:30 ` Long Li
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