RE: [PATCH] isci: correct erroneous for_each_isci_host macro

[Dorau, Lukasz]

On Monday, January 20, 2014 7:26 PM Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
> On Mon, Jan 20, 2014 at 8:54 AM, Lukasz Dorau <lukasz.dorau@xxxxxxxxx> wrote:
> > In the first place, the loop 'for' in the macro 'for_each_isci_host'
> > (drivers/scsi/isci/host.h:314) is incorrect, because it accesses
> > the 3rd element of 2 element array. After the 2nd iteration it executes
> > the instruction:
> >         ihost = to_pci_info(pdev)->hosts[2]
> > (while the size of the 'hosts' array equals 2) and reads an
> > out of range element.
> >
> > In the second place, because of the following GCC v4.8 bug:
> > http://marc.info/?l=linux-kernel&m=138998871911336&w=2
> > this loop is incorrectly compiled by GCC v4.8.
> > As a result, on platforms with two SCU controllers,
> > the loop at drivers/scsi/isci/init.c:717 is executed
> > more times than it can be (for i=0,1 and 2).
> > It causes the following oops after 'rmmod isci':
> >
> 
> Surprised those bugs lasted this long... some comments below.
> 
> > BUG: unable to handle kernel NULL pointer dereference at (null)
> > IP: [<ffffffff8131360b>] __list_add+0x1b/0xc0
> > Oops: 0000 [#1] SMP
> > RIP: 0010:[<ffffffff8131360b>]  [<ffffffff8131360b>] __list_add+0x1b/0xc0
> > Call Trace:
> >   [<ffffffff81661b84>] __mutex_lock_slowpath+0x114/0x1b0
> >   [<ffffffff81661c3f>] mutex_lock+0x1f/0x30
> >   [<ffffffffa03e97cb>] sas_disable_events+0x1b/0x50 [libsas]
> >   [<ffffffffa03e9818>] sas_unregister_ha+0x18/0x60 [libsas]
> >   [<ffffffffa040316e>] isci_unregister+0x1e/0x40 [isci]
> >   [<ffffffffa0403efd>] isci_pci_remove+0x5d/0x100 [isci]
> >   [<ffffffff813391cb>] pci_device_remove+0x3b/0xb0
> >   [<ffffffff813fbf7f>] __device_release_driver+0x7f/0xf0
> >   [<ffffffff813fc8f8>] driver_detach+0xa8/0xb0
> >   [<ffffffff813fbb8b>] bus_remove_driver+0x9b/0x120
> >   [<ffffffff813fcf2c>] driver_unregister+0x2c/0x50
> >   [<ffffffff813381f3>] pci_unregister_driver+0x23/0x80
> >   [<ffffffffa04152f8>] isci_exit+0x10/0x1e [isci]
> >   [<ffffffff810d199b>] SyS_delete_module+0x16b/0x2d0
> >   [<ffffffff81012a21>] ? do_notify_resume+0x61/0xa0
> >   [<ffffffff8166ce29>] system_call_fastpath+0x16/0x1b
> >
> > The loop has been corrected.
> > This patch fixes the above oops.
> >
> > Signed-off-by: Lukasz Dorau <lukasz.dorau@xxxxxxxxx>
> > Reviewed-by: Maciej Patelczyk <maciej.patelczyk@xxxxxxxxx>
> > Tested-by: Lukasz Dorau <lukasz.dorau@xxxxxxxxx>
> > Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> > Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
> > Cc: <stable@xxxxxxxxxxxxxxx>
> > ---
> >  drivers/scsi/isci/host.h |    6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/scsi/isci/host.h b/drivers/scsi/isci/host.h
> > index 4911310..95adf31 100644
> > --- a/drivers/scsi/isci/host.h
> > +++ b/drivers/scsi/isci/host.h
> > @@ -311,9 +311,9 @@ static inline struct Scsi_Host *to_shost(struct isci_host
> *ihost)
> >  }
> >
> >  #define for_each_isci_host(id, ihost, pdev) \
> > -       for (id = 0, ihost = to_pci_info(pdev)->hosts[id]; \
> > -            id < ARRAY_SIZE(to_pci_info(pdev)->hosts) && ihost; \
> > -            ihost = to_pci_info(pdev)->hosts[++id])
> > +       for (id = 0, ihost = to_pci_info(pdev)->hosts[0]; \
> 
> No need to initialize ihost here since we assign and check it later.
> 
> > +            (id < ARRAY_SIZE(to_pci_info(pdev)->hosts)) && \
> 
> Just use SCI_MAX_CONTROLLERS here.
> 
> > +            (ihost = to_pci_info(pdev)->hosts[id]); id++)
> 
> --

Thanks, Dan.
I will submit the second version of the patch.

Lukasz

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