[PATCH v3] mpt3sas: correct reset of smid while clearing scsi tracker

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In mpt3sas_base_clear_st() function smid value is reset in
wrong line, i.e. driver should reset smid value to zero after decrementing
chain_offset counter in chain_lookup table but in current code, driver is
resetting smid value before decrementing the chain_offset counter. Which we
are correcting with this patch.

v1 changelog:
Added memory barriers before & after atomic_set() API.

v2 changelog:
Added proper comments to describe the need of using
smp_mb__before_atomic() & smp_mb__after_atomic() APIs
in the driver before calling these APIs.

v3 changelog:
Replaced smp_mb__before_atomic() & smp_mb__after_atomic() APIs
with smp_mb() APIs.

Used smp_mb() API in mpt3sas_base_clear_st() to make sure that
smid is reset to zero only after corresponding smid pool's
chain_offset in chain lookup table is reset to zero.

Used smp_mb() API in _base_get_chain_buffer_tracker()
to make sure that proper chain tracker is retrieved from the
corresponding smid's pool from chain table before incrementing
smid pool's chain offset value.

Signed-off-by: Sreekanth Reddy <sreekanth.reddy@xxxxxxxxxxxx>
---
 drivers/scsi/mpt3sas/mpt3sas_base.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/mpt3sas/mpt3sas_base.c b/drivers/scsi/mpt3sas/mpt3sas_base.c
index 902610d..2c5a5b4 100644
--- a/drivers/scsi/mpt3sas/mpt3sas_base.c
+++ b/drivers/scsi/mpt3sas/mpt3sas_base.c
@@ -1702,6 +1702,13 @@ static int mpt3sas_remove_dead_ioc_func(void *arg)
 		return NULL;
 
 	chain_req = &ioc->chain_lookup[smid - 1].chains_per_smid[chain_offset];
+
+	/*
+	 * Added memory barrier to make sure that correct chain tracker
+	 * is retrieved before incrementing the smid pool's chain_offset
+	 * value in chain lookup table.
+	 */
+	smp_mb();
 	atomic_inc(&ioc->chain_lookup[smid - 1].chain_offset);
 	return chain_req;
 }
@@ -3283,8 +3290,15 @@ void mpt3sas_base_clear_st(struct MPT3SAS_ADAPTER *ioc,
 		return;
 	st->cb_idx = 0xFF;
 	st->direct_io = 0;
-	st->smid = 0;
 	atomic_set(&ioc->chain_lookup[st->smid - 1].chain_offset, 0);
+
+	/*
+	 * Added memory barrier to make sure that smid is set to zero
+	 * only after resetting corresponding smid pool's chain_offset to zero
+	 * in chain lookup table.
+	 */
+	smp_mb();
+	st->smid = 0;
 }
 
 /**
-- 
1.8.3.1




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