Re: [PATCH 3/4] PCI/hotplug: reset_lock is not required synchronizing with irq thread

Ilpo Järvinen
2025-03-14T11:18:14Z

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On Fri, 14 Mar 2025, Lukas Wunner wrote:

> On Thu, Mar 13, 2025 at 04:23:32PM +0200, Ilpo Järvinen wrote:
> > Disabling HPIE (Hot-Plug Interrupt Enable) and synchronizing with irq
> > handling in pciehp_reset_slot() is enough to ensure no pending events
> > are processed during the slot reset. Thus, there is no need to take
> > reset_lock in the IRQ thread.
> [...]
> > --- a/drivers/pci/hotplug/pciehp_hpc.c
> > +++ b/drivers/pci/hotplug/pciehp_hpc.c
> > @@ -748,12 +748,10 @@ static irqreturn_t pciehp_ist(int irq, void *dev_id)
> > * Disable requests have higher priority than Presence Detect Changed
> > * or Data Link Layer State Changed events.
> > */
> > - down_read_nested(&ctrl->reset_lock, ctrl->depth);
> > if (events & DISABLE_SLOT)
> > pciehp_handle_disable_request(ctrl);
> > else if (events & (PCI_EXP_SLTSTA_PDC | PCI_EXP_SLTSTA_DLLSC))
> > pciehp_handle_presence_or_link_change(ctrl, events);
> > - up_read(&ctrl->reset_lock);
> >
> > ret = IRQ_HANDLED;
> > out:
>
> The release and re-acquisition of reset_lock in
> pciehp_configure_device() and pciehp_unconfigure_device()
> needs to be removed as well if the above hunk is applied.

Ah, right. I also now removed reset_lock from
pciehp_ignore_dpc_link_change() that is directly called from pciehp_ist().

This leaves reset_lock only into pciehp_free_irq(), pciehp_reset_slot(),
and pciehp_check_presence(). It seems to me pciehp_check_presence()
requires keeping reset_lock as is. The former two could have synchronized
with a mutex and shorter critical sections in pciehp_reset_slot() but it
doesn't look worth the effort (IMO) to divide reset_lock into two to
realize that.

> But please wait a little while before respinning so that I can
> think through the whole series.

Sure, take your time. :-)

--
i.