linux-kernel - Re: [PATCH v7 4/5] PCI: only return true when dev io state is really changed

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Date:   Wed, 7 Oct 2020 15:50:45 +0800
From:   Ethan Zhao <xerces.zhao@...il.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Ethan Zhao <haifeng.zhao@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>, Oliver <oohall@...il.com>,
        ruscur@...sell.cc, Lukas Wunner <lukas@...ner.de>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Stuart Hayes <stuart.w.hayes@...il.com>,
        Alexandru Gagniuc <mr.nuke.me@...il.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        linux-pci <linux-pci@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Raj, Ashok" <ashok.raj@...ux.intel.com>,
        Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@...el.com>
Subject: Re: [PATCH v7 4/5] PCI: only return true when dev io state is really changed

Bjorn,

On Sun, Oct 4, 2020 at 12:44 AM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> On Sat, Oct 03, 2020 at 03:55:13AM -0400, Ethan Zhao wrote:
> > When uncorrectable error happens, AER driver and DPC driver interrupt
> > handlers likely call
> >
> >    pcie_do_recovery()
> >    ->pci_walk_bus()
> >      ->report_frozen_detected()
> >
> > with pci_channel_io_frozen the same time.
> >    If pci_dev_set_io_state() return true even if the original state is
> > pci_channel_io_frozen, that will cause AER or DPC handler re-enter
> > the error detecting and recovery procedure one after another.
> >    The result is the recovery flow mixed between AER and DPC.
> > So simplify the pci_dev_set_io_state() function to only return true
> > when dev->error_state is really changed.
> >
> > Signed-off-by: Ethan Zhao <haifeng.zhao@...el.com>
> > Tested-by: Wen Jin <wen.jin@...el.com>
> > Tested-by: Shanshan Zhang <ShanshanX.Zhang@...el.com>
> > Reviewed-by: Alexandru Gagniuc <mr.nuke.me@...il.com>
> > Reviewed-by: Andy Shevchenko <andy.shevchenko@...il.com>
> > ---
> > Changnes:
> >  v2: revise description and code according to suggestion from Andy.
> >  v3: change code to simpler.
> >  v4: no change.
> >  v5: no change.
> >  v6: no change.
> >  v7: changed based on Bjorn's code and truth table.
> >
> >  drivers/pci/pci.h | 53 ++++++++++++++++++-----------------------------
> >  1 file changed, 20 insertions(+), 33 deletions(-)
> >
> > diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> > index 455b32187abd..47af1ff2a286 100644
> > --- a/drivers/pci/pci.h
> > +++ b/drivers/pci/pci.h
> > @@ -354,44 +354,31 @@ struct pci_sriov {
> >   *
> >   * Must be called with device_lock held.
> >   *
> > - * Returns true if state has been changed to the requested state.
> > + * Returns true if state has been really changed to the requested state.
> >   */
> >  static inline bool pci_dev_set_io_state(struct pci_dev *dev,
> >                                       pci_channel_state_t new)
> >  {
> > -     bool changed = false;
> > -
> >       device_lock_assert(&dev->dev);
> > -     switch (new) {
> > -     case pci_channel_io_perm_failure:
> > -             switch (dev->error_state) {
> > -             case pci_channel_io_frozen:
> > -             case pci_channel_io_normal:
> > -             case pci_channel_io_perm_failure:
> > -                     changed = true;
> > -                     break;
> > -             }
> > -             break;
> > -     case pci_channel_io_frozen:
> > -             switch (dev->error_state) {
> > -             case pci_channel_io_frozen:
> > -             case pci_channel_io_normal:
> > -                     changed = true;
> > -                     break;
> > -             }
> > -             break;
> > -     case pci_channel_io_normal:
> > -             switch (dev->error_state) {
> > -             case pci_channel_io_frozen:
> > -             case pci_channel_io_normal:
> > -                     changed = true;
> > -                     break;
> > -             }
> > -             break;
> > -     }
> > -     if (changed)
> > -             dev->error_state = new;
> > -     return changed;
> > +
> > +/*
> > + *                   Truth table:
> > + *                   requested new state
> > + *     current          ------------------------------------------
> > + *     state            normal         frozen         perm_failure
> > + *     ------------  +  -------------  -------------  ------------
> > + *     normal        |  normal         frozen         perm_failure
> > + *     frozen        |  normal         frozen         perm_failure
> > + *     perm_failure  |  perm_failure*  perm_failure*  perm_failure
> > + */
> > +
> > +     if (dev->error_state == pci_channel_io_perm_failure)
> > +             return false;
> > +     else if (dev->error_state == new)
> > +             return false;
> > +
> > +     dev->error_state = new;
> > +     return true;
>
> No, you missed the point.  I want
>
>   1) One patch that converts the "switch" to the shorter "if"
>      statements.  This one will be big and ugly, but should not change
>      the functionality at all, and it should be pretty easy to verify
>      that since there aren't very many states involved.
>
>      Since this one is pure code simplification, the commit log won't
>      say anything at all about AER or DPC or their requirements
>      because it's not changing any behavior.
>
>   2) A separate patch that's tiny and makes whatever functional change
>      you need.

       Make sense, clear,  this time.

     Thanks,
     Ethan
>
> >  }
> >
> >  static inline int pci_dev_set_disconnected(struct pci_dev *dev, void *unused)
> > --
> > 2.18.4
> >