From: Benjamin Block bblock@linux.ibm.com
[ Upstream commit 484647088826f2f651acbda6bcf9536b8a466703 ]
GCC v9 emits this warning: CC drivers/s390/scsi/zfcp_erp.o drivers/s390/scsi/zfcp_erp.c: In function 'zfcp_erp_action_enqueue': drivers/s390/scsi/zfcp_erp.c:217:26: warning: 'erp_action' may be used uninitialized in this function [-Wmaybe-uninitialized] 217 | struct zfcp_erp_action *erp_action; | ^~~~~~~~~~
This is a possible false positive case, as also documented in the GCC documentations: https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wmaybe-uniniti...
The actual code-sequence is like this: Various callers can invoke the function below with the argument "want" being one of: ZFCP_ERP_ACTION_REOPEN_ADAPTER, ZFCP_ERP_ACTION_REOPEN_PORT_FORCED, ZFCP_ERP_ACTION_REOPEN_PORT, or ZFCP_ERP_ACTION_REOPEN_LUN.
zfcp_erp_action_enqueue(want, ...) ... need = zfcp_erp_required_act(want, ...) need = want ... maybe: need = ZFCP_ERP_ACTION_REOPEN_PORT maybe: need = ZFCP_ERP_ACTION_REOPEN_ADAPTER ... return need ... zfcp_erp_setup_act(need, ...) struct zfcp_erp_action *erp_action; // <== line 217 ... switch(need) { case ZFCP_ERP_ACTION_REOPEN_LUN: ... erp_action = &zfcp_sdev->erp_action; WARN_ON_ONCE(erp_action->port != port); // <== access ... break; case ZFCP_ERP_ACTION_REOPEN_PORT: case ZFCP_ERP_ACTION_REOPEN_PORT_FORCED: ... erp_action = &port->erp_action; WARN_ON_ONCE(erp_action->port != port); // <== access ... break; case ZFCP_ERP_ACTION_REOPEN_ADAPTER: ... erp_action = &adapter->erp_action; WARN_ON_ONCE(erp_action->port != NULL); // <== access ... break; } ... WARN_ON_ONCE(erp_action->adapter != adapter); // <== access
When zfcp_erp_setup_act() is called, 'need' will never be anything else than one of the 4 possible enumeration-names that are used in the switch-case, and 'erp_action' is initialized for every one of them, before it is used. Thus the warning is a false positive, as documented.
We introduce the extra if{} in the beginning to create an extra code-flow, so the compiler can be convinced that the switch-case will never see any other value.
BUG_ON()/BUG() is intentionally not used to not crash anything, should this ever happen anyway - right now it's impossible, as argued above; and it doesn't introduce a 'default:' switch-case to retain warnings should 'enum zfcp_erp_act_type' ever be extended and no explicit case be introduced. See also v5.0 commit 399b6c8bc9f7 ("scsi: zfcp: drop old default switch case which might paper over missing case").
Signed-off-by: Benjamin Block bblock@linux.ibm.com Reviewed-by: Jens Remus jremus@linux.ibm.com Reviewed-by: Steffen Maier maier@linux.ibm.com Signed-off-by: Martin K. Petersen martin.petersen@oracle.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/s390/scsi/zfcp_erp.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/drivers/s390/scsi/zfcp_erp.c b/drivers/s390/scsi/zfcp_erp.c index e8fc28dba8df..96f0d34e9459 100644 --- a/drivers/s390/scsi/zfcp_erp.c +++ b/drivers/s390/scsi/zfcp_erp.c @@ -11,6 +11,7 @@ #define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
#include <linux/kthread.h> +#include <linux/bug.h> #include "zfcp_ext.h" #include "zfcp_reqlist.h"
@@ -217,6 +218,12 @@ static struct zfcp_erp_action *zfcp_erp_setup_act(enum zfcp_erp_act_type need, struct zfcp_erp_action *erp_action; struct zfcp_scsi_dev *zfcp_sdev;
+ if (WARN_ON_ONCE(need != ZFCP_ERP_ACTION_REOPEN_LUN && + need != ZFCP_ERP_ACTION_REOPEN_PORT && + need != ZFCP_ERP_ACTION_REOPEN_PORT_FORCED && + need != ZFCP_ERP_ACTION_REOPEN_ADAPTER)) + return NULL; + switch (need) { case ZFCP_ERP_ACTION_REOPEN_LUN: zfcp_sdev = sdev_to_zfcp(sdev);