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From: Michael Kelley <mikelley@microsoft.com>
To: Long Li <longli@microsoft.com>, Wei Liu <wei.liu@kernel.org>,
	"longli@linuxonhyperv.com" <longli@linuxonhyperv.com>
Cc: "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 16:50:28 +0000	[thread overview]
Message-ID: <MWHPR21MB1593E4B1051F96DB6E715C0CD7C79@MWHPR21MB1593.namprd21.prod.outlook.com> (raw)
In-Reply-To: <BY5PR21MB1506B6865DA2DA9948CEA8ADCEC69@BY5PR21MB1506.namprd21.prod.outlook.com>

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.

Michael

  reply	other threads:[~2021-08-26 16:50 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-24  7:20 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 [this message]
2021-08-26 19:41           ` Wei Liu
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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