ib_srp: Fix a race condition

Avoid that the scmnd->scsi_done(scmnd) call in srp_process_rsp()
can trigger a crash by being invoked with scsi_done == NULL. That
could happen if a reply is received during or after a command abort.

Reported-by: Joseph Glanville <joseph.glanville@orionvm.com.au>
Reference: http://marc.info/?l=linux-rdma&m=134314367801595
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Acked-by: David Dillow <dillowda@ornl.gov>
Cc: Roland Dreier <roland@purestorage.com>
Cc: <stable@vger.kernel.org>
ib_srp: Enlarge block layer timeout

Enlarge the block layer timeout for disks such that it is above
the InfiniBand transport layer timeout.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: David Dillow <dillowda@ornl.gov>
Cc: Roland Dreier <roland@purestorage.com>
ib_srp: Move QP state check into srp_send_tsk_mgmt()

Test the QP state inside srp_send_tsk_mgmt() instead of letting each
caller perform that test.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: David Dillow <dillowda@ornl.gov>
Cc: Roland Dreier <roland@purestorage.com>
ib_srp: Stop queueing if QP in error

Fail SCSI commands if the QP between initiator and target is in the
error state. For connections monitored by the multipath software
the result is that multipathd doesn't have to wait until the SCSI
timeout has expired to find out that a path has failed.  Also,
introduce the function srp_handle_qp_err(), change the type of
qp_in_error from int into bool and move the initialization of that
variable from srp_reconnect_target() to srp_connect_target().

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: David Dillow <dillowda@ornl.gov>
Cc: Roland Dreier <roland@purestorage.com>
ib_srp: Eliminate state SRP_TARGET_CONNECTING

Block the SCSI host while reconnecting instead of representing
the reconnection activity as a distinct SRP target state. This
allows to eliminate the target state SRP_TARGET_CONNECTING.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: David Dillow <dillowda@ornl.gov>
Cc: Roland Dreier <roland@purestorage.com>
ib_srp: Suppress superfluous error messages

Keep track of the connection state. Only report QP errors while
connected. Only invoke ib_send_cm_dreq() when connected such that
invoking srp_disconnect_target() after having received a DREQ
does not cause an error message to be printed.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: David Dillow <dillowda@ornl.gov>
Cc: Roland Dreier <roland@purestorage.com>
ib_srp: Avoid that SCSI error handling triggers a crash

Sending any data over a queue pair associated with a closed
connection is wrong. The HCA will send the data anyway and such
data may be sent to another system to a queue pair that is in use.
The data will get processed and a response will be sent back. That
can result in ib_srp complaining about "Null scmnd for RSP ..."
followed by a kernel oops.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: David Dillow <dillowda@ornl.gov>
Cc: Roland Dreier <roland@purestorage.com>
ib_srp: Introduce the helper function srp_remove_target()

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: David Dillow <dillowda@ornl.gov>
Cc: Roland Dreier <roland@purestorage.com>
ib_srp: Eliminate state SRP_TARGET_DEAD

Only queue removal work after having changed the target state
into SRP_TARGET_REMOVED and not if that state was already equal
to SRP_TARGET_REMOVED. That allows to remove the state
SRP_TARGET_DEAD. Add a call to srp_disconnect_target() in
srp_remove_target() - due to previous changes it is now safe to
invoke that last function even if the IB connection has already
been disconnected. This change allows to replace the target
removal code in srp_remove_one() by an (indirect) call to
srp_remove_target(). Rename srp_target_port.work into
srp_target_port.remove_work to reflect its usage.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: David Dillow <dillowda@ornl.gov>
Cc: Roland Dreier <roland@purestorage.com>
ib_srp: Keep processing commands during scsi_remove_host()

Some SCSI upper layer drivers, e.g. sd, issue SCSI commands from
inside scsi_remove_host() (see also the sd_shutdown() call in
sd_remove()). Make sure that these commands have a chance to reach
the SCSI device.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: David Dillow <dillowda@ornl.gov>
Cc: Roland Dreier <roland@purestorage.com>
ib_srp: Make srp_disconnect_target() wait for IB completions

Modify srp_disconnect_target() such that it waits until it is
sure that no new IB completions will be received anymore.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: David Dillow <dillowda@ornl.gov>
Cc: Roland Dreier <roland@purestorage.com>
ib_srp: Document sysfs attributes

Document the sysfs attributes of the SRP initiator (ib_srp) according
to the rules specified in Documentation/ABI/README.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: David Dillow <dillowda@ornl.gov>
Cc: Roland Dreier <roland@purestorage.com>
srp_transport: Fix atttribute registration

Register transport attributes after the attribute array has been
set up instead of before. The current code can trigger a race
condition because the code reading the attribute array can run
on another thread than the code that initialized that array.
Make sure that any code reading the attribute array will see all
values written into that array.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: Robert Jennings <rcj@linux.vnet.ibm.com>
Cc: David Dillow <dillowda@ornl.gov>
Cc: Roland Dreier <roland@purestorage.com>
Cc: <stable@kernel.org>
srp_transport: Simplify attribute initialization code

Eliminate the private_rport_attrs[] array and the SETUP_*() macros
used to set up that array since the information in that array
duplicates the information in the static device attributes. Also,
verify whether SRP_RPORT_ATTRS is large enough since it is easy
to forget to update that macro when adding new attributes.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: Robert Jennings <rcj@linux.vnet.ibm.com>
Cc: David Dillow <dillowda@ornl.gov>
Cc: Roland Dreier <roland@purestorage.com>
srp_transport: Document sysfs attributes

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: Robert Jennings <rcj@linux.vnet.ibm.com>
Cc: David Dillow <dillowda@ornl.gov>
Cc: Roland Dreier <roland@purestorage.com>
ib_srp: Allow SRP disconnect through sysfs

Make it possible to disconnect the IB RC connection used by the
SRP protocol to communicate with a target.

Let the SRP transport layer create a sysfs "delete" attribute for
initiator drivers that support this functionality.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: David Dillow <dillowda@ornl.gov>
Cc: Roland Dreier <roland@purestorage.com>
Cc: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: Robert Jennings <rcj@linux.vnet.ibm.com>
ib_srp: Introduce a temporary variable in srp_remove_target()

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: David Dillow <dillowda@ornl.gov>
Cc: Roland Dreier <roland@purestorage.com>
ib_srp: Maintain a single connection per I_T nexus

The sysfs attribute 'add_target' may be used to relogin to a
target. An SRP target that receives a second login request from
an initiator will disconnect the previous connection. So before
trying to reconnect, check whether another connection to the
same SRP target identifier already exists. If so, remove the
target port.  Add a target to the target list before connecting
instead of after such that this algorithm has a chance to work.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: David Dillow <dillowda@ornl.gov>
Cc: Roland Dreier <roland@purestorage.com>
srp_transport: Add transport layer error handling

Add the necessary functions in the SRP transport module to allow
an SRP initiator driver to implement transport error handling.
This includes:
- Support for implementing fast_io_fail_tmo, the time that should
  elapse after having detected a transport layer problem and
  before failing I/O.
- Support for implementing dev_loss_tmo, the time that should
  elapse after having detected a transport layer problem and
  before removing a remote port.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: Robert Jennings <rcj@linux.vnet.ibm.com>
Cc: David Dillow <dillowda@ornl.gov>
ib_srp: Add dev_loss_tmo support

Remove an SRP host if either dev_loss_tmo expired or the target
closed the IB connection.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: David Dillow <dillowda@ornl.gov>
Cc: Roland Dreier <roland@purestorage.com>