3.16.52-rc1 review patch. If anyone has any objections, please let me know.
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From: Steffen Maier maier@linux.vnet.ibm.com
commit ab31fd0ce65ec93828b617123792c1bb7c6dcc42 upstream.
v4.10 commit 6f2ce1c6af37 ("scsi: zfcp: fix rport unblock race with LUN recovery") extended accessing parent pointer fields of struct zfcp_erp_action for tracing. If an erp_action has never been enqueued before, these parent pointer fields are uninitialized and NULL. Examples are zfcp objects freshly added to the parent object's children list, before enqueueing their first recovery subsequently. In zfcp_erp_try_rport_unblock(), we iterate such list. Accessing erp_action fields can cause a NULL pointer dereference. Since the kernel can read from lowcore on s390, it does not immediately cause a kernel page fault. Instead it can cause hangs on trying to acquire the wrong erp_action->adapter->dbf->rec_lock in zfcp_dbf_rec_action_lvl() ^bogus^ while holding already other locks with IRQs disabled.
Real life example from attaching lots of LUNs in parallel on many CPUs:
crash> bt 17723 PID: 17723 TASK: ... CPU: 25 COMMAND: "zfcperp0.0.1800" LOWCORE INFO: -psw : 0x0404300180000000 0x000000000038e424 -function : _raw_spin_lock_wait_flags at 38e424 ... #0 [fdde8fc90] zfcp_dbf_rec_action_lvl at 3e0004e9862 [zfcp] #1 [fdde8fce8] zfcp_erp_try_rport_unblock at 3e0004dfddc [zfcp] #2 [fdde8fd38] zfcp_erp_strategy at 3e0004e0234 [zfcp] #3 [fdde8fda8] zfcp_erp_thread at 3e0004e0a12 [zfcp] #4 [fdde8fe60] kthread at 173550 #5 [fdde8feb8] kernel_thread_starter at 10add2
zfcp_adapter zfcp_port zfcp_unit <address>, 0x404040d600000000 scsi_device NULL, returning early! zfcp_scsi_dev.status = 0x40000000 0x40000000 ZFCP_STATUS_COMMON_RUNNING
crash> zfcp_unit <address> struct zfcp_unit { erp_action = { adapter = 0x0, port = 0x0, unit = 0x0, }, }
zfcp_erp_action is always fully embedded into its container object. Such container object is never moved in its object tree (only add or delete). Hence, erp_action parent pointers can never change.
To fix the issue, initialize the erp_action parent pointers before adding the erp_action container to any list and thus before it becomes accessible from outside of its initializing function.
In order to also close the time window between zfcp_erp_setup_act() memsetting the entire erp_action to zero and setting the parent pointers again, drop the memset and instead explicitly initialize individually all erp_action fields except for parent pointers. To be extra careful not to introduce any other unintended side effect, even keep zeroing the erp_action fields for list and timer. Also double-check with WARN_ON_ONCE that erp_action parent pointers never change, so we get to know when we would deviate from previous behavior.
Signed-off-by: Steffen Maier maier@linux.vnet.ibm.com Fixes: 6f2ce1c6af37 ("scsi: zfcp: fix rport unblock race with LUN recovery") Reviewed-by: Benjamin Block bblock@linux.vnet.ibm.com Signed-off-by: Martin K. Petersen martin.petersen@oracle.com Signed-off-by: Ben Hutchings ben@decadent.org.uk --- drivers/s390/scsi/zfcp_aux.c | 5 +++++ drivers/s390/scsi/zfcp_erp.c | 18 +++++++++++------- drivers/s390/scsi/zfcp_scsi.c | 5 +++++ 3 files changed, 21 insertions(+), 7 deletions(-)
--- a/drivers/s390/scsi/zfcp_aux.c +++ b/drivers/s390/scsi/zfcp_aux.c @@ -356,6 +356,8 @@ struct zfcp_adapter *zfcp_adapter_enqueu INIT_WORK(&adapter->scan_work, zfcp_fc_scan_ports); INIT_WORK(&adapter->ns_up_work, zfcp_fc_sym_name_update);
+ adapter->erp_action.adapter = adapter; + if (zfcp_qdio_setup(adapter)) goto failed;
@@ -512,6 +514,9 @@ struct zfcp_port *zfcp_port_enqueue(stru port->dev.groups = zfcp_port_attr_groups; port->dev.release = zfcp_port_release;
+ port->erp_action.adapter = adapter; + port->erp_action.port = port; + if (dev_set_name(&port->dev, "0x%016llx", (unsigned long long)wwpn)) { kfree(port); goto err_out; --- a/drivers/s390/scsi/zfcp_erp.c +++ b/drivers/s390/scsi/zfcp_erp.c @@ -193,9 +193,8 @@ static struct zfcp_erp_action *zfcp_erp_ atomic_set_mask(ZFCP_STATUS_COMMON_ERP_INUSE, &zfcp_sdev->status); erp_action = &zfcp_sdev->erp_action; - memset(erp_action, 0, sizeof(struct zfcp_erp_action)); - erp_action->port = port; - erp_action->sdev = sdev; + WARN_ON_ONCE(erp_action->port != port); + WARN_ON_ONCE(erp_action->sdev != sdev); if (!(atomic_read(&zfcp_sdev->status) & ZFCP_STATUS_COMMON_RUNNING)) act_status |= ZFCP_STATUS_ERP_CLOSE_ONLY; @@ -208,8 +207,8 @@ static struct zfcp_erp_action *zfcp_erp_ zfcp_erp_action_dismiss_port(port); atomic_set_mask(ZFCP_STATUS_COMMON_ERP_INUSE, &port->status); erp_action = &port->erp_action; - memset(erp_action, 0, sizeof(struct zfcp_erp_action)); - erp_action->port = port; + WARN_ON_ONCE(erp_action->port != port); + WARN_ON_ONCE(erp_action->sdev != NULL); if (!(atomic_read(&port->status) & ZFCP_STATUS_COMMON_RUNNING)) act_status |= ZFCP_STATUS_ERP_CLOSE_ONLY; break; @@ -219,7 +218,8 @@ static struct zfcp_erp_action *zfcp_erp_ zfcp_erp_action_dismiss_adapter(adapter); atomic_set_mask(ZFCP_STATUS_COMMON_ERP_INUSE, &adapter->status); erp_action = &adapter->erp_action; - memset(erp_action, 0, sizeof(struct zfcp_erp_action)); + WARN_ON_ONCE(erp_action->port != NULL); + WARN_ON_ONCE(erp_action->sdev != NULL); if (!(atomic_read(&adapter->status) & ZFCP_STATUS_COMMON_RUNNING)) act_status |= ZFCP_STATUS_ERP_CLOSE_ONLY; @@ -229,7 +229,11 @@ static struct zfcp_erp_action *zfcp_erp_ return NULL; }
- erp_action->adapter = adapter; + WARN_ON_ONCE(erp_action->adapter != adapter); + memset(&erp_action->list, 0, sizeof(erp_action->list)); + memset(&erp_action->timer, 0, sizeof(erp_action->timer)); + erp_action->step = ZFCP_ERP_STEP_UNINITIALIZED; + erp_action->fsf_req_id = 0; erp_action->action = need; erp_action->status = act_status;
--- a/drivers/s390/scsi/zfcp_scsi.c +++ b/drivers/s390/scsi/zfcp_scsi.c @@ -136,10 +136,15 @@ static int zfcp_scsi_slave_alloc(struct struct zfcp_unit *unit; int npiv = adapter->connection_features & FSF_FEATURE_NPIV_MODE;
+ zfcp_sdev->erp_action.adapter = adapter; + zfcp_sdev->erp_action.sdev = sdev; + port = zfcp_get_port_by_wwpn(adapter, rport->port_name); if (!port) return -ENXIO;
+ zfcp_sdev->erp_action.port = port; + unit = zfcp_unit_find(port, zfcp_scsi_dev_lun(sdev)); if (unit) put_device(&unit->dev);