From: Karsten Graul <kgraul@linux.ibm.com>
Subject: s390/ism: clear dmbe_mask bit before SMC IRQ handling
Patch-mainline: v4.20-rc4
Git-commit: 007b656851ed7f94ba0fa358ac3e5d7705da6846
References: FATE#325698, LTC#167867, bsc#1113481

Description:  net/smc: bugfix and compatibility patches
Symptom:      Random hangs in smc processing:
                user space application hangs in socket send() or recv() call or
                does never get a notification from a select() call.
              Missing compatibility to other platforms:
                confirm rkey and delete rkey processing is required by the
                design, but delete rkey processing is missing. This leads to
                protocol failures when communicating with other platforms like
                zOS. The SMC-D shutdown signal support is missing, so there is
                no detection if the remote peer closed the link group.
              Broken administration of available WR send payload buffers due to
              a use-after-free condition.
Problem:      Misbehaviour regarding the user space api can lead to hang
              situations. SMC is not fully compatible to some other platforms
              due to missing rkey processing and SMC-D shutdown signal support.
Solution:     Fixed protocoll deficiencies by implementing the required rkey
              processing. For SMC-D, the cursors are now handled atomically to
              handle parallel modifications. The SMC-D shutdown signal is now
              processed when received and sent to the remote peer if needed.
              Prereq patches are included.
Reproduction: Run SMC on a loaded system against zOS as peer system.

Upstream-Description:

              s390/ism: clear dmbe_mask bit before SMC IRQ handling

              SMC-D stress workload showed connection stalls. Since the firmware
              decides to skip raising an interrupt if the SBA DMBE mask bit is
              still set, this SBA DMBE mask bit should be cleared before the
              IRQ handling in the SMC code runs. Otherwise there are small windows
              possible with missing interrupts for incoming data.
              SMC-D currently does not care about the old value of the SBA DMBE
              mask.

              Acked-by: Sebastian Ott <sebott@linux.ibm.com>
              Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
              Signed-off-by: David S. Miller <davem@davemloft.net>


Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>
Acked-by: Petr Tesarik <ptesarik@suse.com>
---
 drivers/s390/net/ism_drv.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/s390/net/ism_drv.c
+++ b/drivers/s390/net/ism_drv.c
@@ -415,9 +415,9 @@ static irqreturn_t ism_handle_irq(int ir
 			break;
 
 		clear_bit_inv(bit, bv);
+		ism->sba->dmbe_mask[bit + ISM_DMB_BIT_OFFSET] = 0;
 		barrier();
 		smcd_handle_irq(ism->smcd, bit + ISM_DMB_BIT_OFFSET);
-		ism->sba->dmbe_mask[bit + ISM_DMB_BIT_OFFSET] = 0;
 	}
 
 	if (ism->sba->e) {