Messages in this thread | | | Subject | Re: arch/s390/pci/pci_event.c:101 __zpci_event_availability() error: we previously assumed 'zdev->zbus' could be null (see line 83) | From | Niklas Schnelle <> | Date | Thu, 3 Dec 2020 11:52:48 +0100 |
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On 12/3/20 11:27 AM, Dan Carpenter wrote: > tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master > head: 3bb61aa61828499a7d0f5e560051625fd02ae7e4 > commit: 3047766bc6ec9c6bc9ece85b45a41ff401e8d988 s390/pci: fix enabling a reserved PCI function > > If you fix the issue, kindly add following tag as appropriate > Reported-by: kernel test robot <lkp@intel.com> > Reported-by: Dan Carpenter <dan.carpenter@oracle.com> > > smatch warnings: > arch/s390/pci/pci_event.c:101 __zpci_event_availability() error: we previously assumed 'zdev->zbus' could be null (see line 83) > > vim +101 arch/s390/pci/pci_event.c > > aa3b7c296732b43 Sebastian Ott 2013-12-12 76 static void __zpci_event_availability(struct zpci_ccdf_avail *ccdf) > cbc0dd1f856b52b Jan Glauber 2012-11-29 77 { > cbc0dd1f856b52b Jan Glauber 2012-11-29 78 struct zpci_dev *zdev = get_zdev_by_fid(ccdf->fid); > 9a99649f2a89fdf Sebastian Ott 2016-01-29 79 struct pci_dev *pdev = NULL; > 623bd44d3f277b7 Sebastian Ott 2017-05-09 80 enum zpci_state state; > d795ddad36cbc82 Sebastian Ott 2013-11-15 81 int ret; > cbc0dd1f856b52b Jan Glauber 2012-11-29 82 > 05bc1be6db4b268 Pierre Morel 2020-03-23 @83 if (zdev && zdev->zbus && zdev->zbus->bus) > ^^^^^^^^^ > Check for NULL > > 44510d6fa0c00aa Pierre Morel 2020-04-22 84 pdev = pci_get_slot(zdev->zbus->bus, zdev->devfn); > 9a99649f2a89fdf Sebastian Ott 2016-01-29 85 > 1f1dcbd4f23bd1f Sebastian Ott 2013-10-22 86 zpci_err("avail CCDF:\n"); > 1f1dcbd4f23bd1f Sebastian Ott 2013-10-22 87 zpci_err_hex(ccdf, sizeof(*ccdf)); > cbc0dd1f856b52b Jan Glauber 2012-11-29 88 > cbc0dd1f856b52b Jan Glauber 2012-11-29 89 switch (ccdf->pec) { > 7fc611ff3ff1a0b Sebastian Ott 2015-06-16 90 case 0x0301: /* Reserved|Standby -> Configured */ > 7fc611ff3ff1a0b Sebastian Ott 2015-06-16 91 if (!zdev) { > f606b3ef47c9f87 Pierre Morel 2020-03-25 92 ret = clp_add_pci_device(ccdf->fid, ccdf->fh, 1); > 7fc611ff3ff1a0b Sebastian Ott 2015-06-16 93 break; > 7fc611ff3ff1a0b Sebastian Ott 2015-06-16 94 } > fcf2f402937a669 Sebastian Ott 2013-12-18 95 zdev->fh = ccdf->fh; > f606b3ef47c9f87 Pierre Morel 2020-03-25 96 zdev->state = ZPCI_FN_STATE_CONFIGURED; > 3047766bc6ec9c6 Niklas Schnelle 2020-06-18 97 ret = zpci_enable_device(zdev); > 3047766bc6ec9c6 Niklas Schnelle 2020-06-18 98 if (ret) > 3047766bc6ec9c6 Niklas Schnelle 2020-06-18 99 break; > 3047766bc6ec9c6 Niklas Schnelle 2020-06-18 100 > 3047766bc6ec9c6 Niklas Schnelle 2020-06-18 @101 pdev = pci_scan_single_device(zdev->zbus->bus, zdev->devfn); > ^^^^^^^^^^^^^^^^ > Unchecked dereference
First, thanks for reporting this is definitely appreciated! We have also seen the same smatch report internally and I determined that this is a false positive.
This is because the existing zdev->zbus NULL check could already never trigger. Sadly this is all a bit hard to see but let me try to share my reasoning here. That said, we do plan a couple of cleanups/rework here that will also see the removal of the zdev->zbus NULL check at the start of the function.
The existing check is here:
76 static void __zpci_event_availability(struct zpci_ccdf_avail *ccdf) 77 { 78 struct zpci_dev *zdev = get_zdev_by_fid(ccdf->fid); 79 struct pci_dev *pdev = NULL; 80 enum zpci_state state; 81 int ret; 82 83 if (zdev && zdev->zbus && zdev->zbus->bus) 84 pdev = pci_get_slot(zdev->zbus->bus, zdev->devfn);
Now for both the new zdev->zbus->bus dereference and the check in line 83 we check zdev != NULL beforehand. So that's a given. If we have the zdev it came out of get_zdev_by_fid() (line 78) which found it in the zpci_list.
It only ever gets into that list in zpci_create_device() and gets removed if anything in there fails, including zpci_bus_register_device() which when successful has definitely set zdev->zbus != NULL. Furthermore zpci_create_device() is only called in clp_add_pci_device() which is either called during init of zPCI (in the initial CLP List PCI) or from the kthread that handles events via zpci_event_availability() which checks the the initialization is complete. Therefore there is no race for the window in which zpci_create_device() has the zdev in the list but no zbus set. Either way, this is definitely too hard to reason about e.g. we should only add devices to the zpci_list once they are fully initialized and we're working on a redesign of this.
If you prefer a short term fix so this doesn't trigger again we could simply remove the zdev->zbus NULL check.
> ... snip ...
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