Re: [PATCH] mpt3sas: Fix kernel panic observed on soft HBA unplug

[Sreekanth Reddy <sreekanth.reddy@broadcom.com>]

On Wed, Mar 11, 2020 at 4:55 PM Sreekanth Reddy
<sreekanth.reddy@broadcom.com> wrote:
>
> On Wed, Mar 11, 2020 at 4:35 PM Amit Shah <amit@kernel.org> wrote:
> >
> > On Wed, 2020-03-11 at 06:36 -0400, Sreekanth Reddy wrote:
> > > Generic protection fault type kernel panic is observed when user
> > > performs soft(ordered) HBA unplug operation while IOs are running
> > > on drives connected to HBA.
> > >
> > > When user performs ordered HBA removal operation then kernel calls
> > > PCI device's .remove() call back function where driver is flushing
> > > out
> > > all the outstanding SCSI IO commands with DID_NO_CONNECT host byte
> > > and
> > > also un-maps sg buffers allocated for these IO commands.
> > > But in the ordered HBA removal case (unlike of real HBA hot unplug)
> > > HBA device is still alive and hence HBA hardware is performing the
> > > DMA operations to those buffers on the system memory which are
> > > already
> > > unmapped while flushing out the outstanding SCSI IO commands
> > > and this leads to Kernel panic.
> > >
> > > Fix:
> > > Don't flush out the outstanding IOs from .remove() path in case of
> > > ordered HBA removal since HBA will be still alive in this case and
> > > it can complete the outstanding IOs. Flush out the outstanding IOs
> > > only in case physical HBA hot unplug where their won't be any
> > > communication with the HBA.
> >
> > Can you please point to the commit that introduces the bug?
>
> Sure I will add the commit ID which introduced this bug in the next patch.
>
> >
> > >
> > > Cc: stable@vger.kernel.org
> > > Signed-off-by: Sreekanth Reddy <sreekanth.reddy@broadcom.com>
> > > ---
> > >  drivers/scsi/mpt3sas/mpt3sas_scsih.c | 8 ++++----
> > >  1 file changed, 4 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/scsi/mpt3sas/mpt3sas_scsih.c
> > > b/drivers/scsi/mpt3sas/mpt3sas_scsih.c
> > > index 778d5e6..04a40af 100644
> > > --- a/drivers/scsi/mpt3sas/mpt3sas_scsih.c
> > > +++ b/drivers/scsi/mpt3sas/mpt3sas_scsih.c
> > > @@ -9908,8 +9908,8 @@ static void scsih_remove(struct pci_dev *pdev)
> > >
> > >       ioc->remove_host = 1;
> > >
> > > -     mpt3sas_wait_for_commands_to_complete(ioc);
> > > -     _scsih_flush_running_cmds(ioc);
> > > +     if (!pci_device_is_present(pdev))
> > > +             _scsih_flush_running_cmds(ioc);
> > >
> > >       _scsih_fw_event_cleanup_queue(ioc);
> > >
> > > @@ -9992,8 +9992,8 @@ static void scsih_remove(struct pci_dev *pdev)
> >
> > Just a note: this function is scsih_shutdown().  Doesn't block
> > application of the patch, though.  Just wondering how the patch was
> > created.

I got your query now,  yes this hunk change is in scsih_shutdown()
function. I am not sure why scsih_remove name is getting displayed
here in this hunk. I have used 'git format-patch' to generate the
patch.

>
> Sorry I didn't get you. Can you please elaborate your query?
>
> >
> > >
> > >       ioc->remove_host = 1;
> > >
> > > -     mpt3sas_wait_for_commands_to_complete(ioc);
> > > -     _scsih_flush_running_cmds(ioc);
> > > +     if (!pci_device_is_present(pdev))
> > > +             _scsih_flush_running_cmds(ioc);
> > >
> > >       _scsih_fw_event_cleanup_queue(ioc);
> > >
> >