Re: [PATCH] scsi: libsas: Check and update the link rate during discovery

[error27@gmail.com]

Hi Yihang,

https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Yihang-Li/scsi-libsas-Check-and-update-the-link-rate-during-discovery/20221102-180734
base:   https://git.kernel.org/pub/scm/linux/kernel/git/mkp/scsi.git for-next
patch link:    https://lore.kernel.org/r/20221102100555.3537275-1-liyihang9%40huawei.com
patch subject: [PATCH] scsi: libsas: Check and update the link rate during discovery
config: m68k-randconfig-m041-20221102
compiler: m68k-linux-gcc (GCC) 12.1.0

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>
| Reported-by: Dan Carpenter <error27@gmail.com>

New smatch warnings:
drivers/scsi/libsas/sas_expander.c:1962 sas_ex_update_linkrate() warn: iterator used outside loop: 'child'

Old smatch warnings:
drivers/scsi/libsas/sas_expander.c:253 sas_set_ex_phy() error: potential null dereference 'phy->phy'.  (sas_phy_alloc returns null)
drivers/scsi/libsas/sas_expander.c:253 sas_set_ex_phy() error: we previously assumed 'phy->phy' could be null (see line 189)
drivers/scsi/libsas/sas_expander.c:1974 sas_ex_update_linkrate() warn: iterator used outside loop: 'child'

vim +/child +1962 drivers/scsi/libsas/sas_expander.c

39d64046e3dfc7 Yihang Li       2022-11-02  1947  static void sas_ex_update_linkrate(struct domain_device *parent)
39d64046e3dfc7 Yihang Li       2022-11-02  1948  {
39d64046e3dfc7 Yihang Li       2022-11-02  1949  	struct expander_device *ex = &parent->ex_dev;
39d64046e3dfc7 Yihang Li       2022-11-02  1950  	int i = 0, end = ex->num_phys;
39d64046e3dfc7 Yihang Li       2022-11-02  1951  
39d64046e3dfc7 Yihang Li       2022-11-02  1952  	for ( ; i < end; i++) {
39d64046e3dfc7 Yihang Li       2022-11-02  1953  		struct ex_phy *ex_phy = &ex->ex_phy[i];
39d64046e3dfc7 Yihang Li       2022-11-02  1954  		struct domain_device *child;
39d64046e3dfc7 Yihang Li       2022-11-02  1955  
39d64046e3dfc7 Yihang Li       2022-11-02  1956  		list_for_each_entry(child, &parent->ex_dev.children, siblings)
                                                                                    ^^^^^
Imagine this loop exits without finding the correct child.

39d64046e3dfc7 Yihang Li       2022-11-02  1957  			if (SAS_ADDR(child->sas_addr) ==
39d64046e3dfc7 Yihang Li       2022-11-02  1958  			    SAS_ADDR(ex_phy->attached_sas_addr))
39d64046e3dfc7 Yihang Li       2022-11-02  1959  				break;
39d64046e3dfc7 Yihang Li       2022-11-02  1960  
39d64046e3dfc7 Yihang Li       2022-11-02  1961  		if (dev_is_sata(child)) {
                                                                                ^^^^^
That means "child" is not a valid pointer.  Not sure why the warning is
only triggered on the line below instead of here.

39d64046e3dfc7 Yihang Li       2022-11-02 @1962  			if (child->linkrate > parent->min_linkrate) {
39d64046e3dfc7 Yihang Li       2022-11-02  1963  				struct sas_phy_linkrates rates = {
39d64046e3dfc7 Yihang Li       2022-11-02  1964  					.maximum_linkrate = parent->min_linkrate,
39d64046e3dfc7 Yihang Li       2022-11-02  1965  					.minimum_linkrate = parent->min_linkrate,
39d64046e3dfc7 Yihang Li       2022-11-02  1966  				};
39d64046e3dfc7 Yihang Li       2022-11-02  1967  
39d64046e3dfc7 Yihang Li       2022-11-02  1968  				sas_smp_phy_control(parent, i,
39d64046e3dfc7 Yihang Li       2022-11-02  1969  						    PHY_FUNC_LINK_RESET, &rates);
39d64046e3dfc7 Yihang Li       2022-11-02  1970  				ex_phy->phy_change_count = -1;
39d64046e3dfc7 Yihang Li       2022-11-02  1971  			}
39d64046e3dfc7 Yihang Li       2022-11-02  1972  		}
39d64046e3dfc7 Yihang Li       2022-11-02  1973  
39d64046e3dfc7 Yihang Li       2022-11-02  1974  		if (dev_is_expander(child->dev_type)) {
39d64046e3dfc7 Yihang Li       2022-11-02  1975  			child->min_linkrate = min(parent->min_linkrate,
39d64046e3dfc7 Yihang Li       2022-11-02  1976  						  ex_phy->linkrate);
39d64046e3dfc7 Yihang Li       2022-11-02  1977  			child->max_linkrate = max(parent->max_linkrate,
39d64046e3dfc7 Yihang Li       2022-11-02  1978  						  ex_phy->linkrate);
39d64046e3dfc7 Yihang Li       2022-11-02  1979  			child->linkrate = min(ex_phy->linkrate,
39d64046e3dfc7 Yihang Li       2022-11-02  1980  					      child->max_linkrate);
39d64046e3dfc7 Yihang Li       2022-11-02  1981  			ex_phy->phy_change_count = -1;
39d64046e3dfc7 Yihang Li       2022-11-02  1982  		}
39d64046e3dfc7 Yihang Li       2022-11-02  1983  	}
39d64046e3dfc7 Yihang Li       2022-11-02  1984  }

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