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 : 0x040430018000 0x0038e424
-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 , 0x404040d6
scsi_device NULL, returning early!
zfcp_scsi_dev.status = 0x4000
0x4000 ZFCP_STATUS_COMMON_RUNNING
crash> zfcp_unit
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
Fixes: 6f2ce1c6af37 ("scsi: zfcp: fix rport unblock race with LUN recovery")
Cc: #2.6.32+
Reviewed-by: Benjamin Block
---
James, Martin,
it's an important bugfix cut against James' scsi.git fixes branch,
and would be nice if it could make it into 4.14 via rc.
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
@@ -357,6 +357,8 @@ struct zfcp_adapter *zfcp_adapter_enqueu
adapter->next_port_scan = jiffies;
+ adapter->erp_action.adapter = adapter;
+
if (zfcp_qdio_setup(adapter))
goto failed;
@@ -513,6 +515,9 @@ 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_or(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_or(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);
