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

From: Long Li <longli@microsoft.com> Sent: Wednesday, August 25, 2021 1:25 PM

quoted

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