RE: [PATCH] PCI: hv: Fix a bug on removing child devices on the bus

[Michael Kelley]

From: Long Li <longli@xxxxxxxxxxxxx> 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