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Subject[PATCH 20/88] iscsi-target: Fix immediate queue starvation regression with DATAIN
Date
3.5.7.8 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Nicholas Bellinger <nab@linux-iscsi.org>

commit fd3a9025c0349bc9b01d627529f54e6e1e389015 upstream.

This patch addresses a v3.5+ regression in iscsi-target where TX thread
process context -> handle_response_queue() execution is allowed to run
unbounded while servicing constant outgoing flow of ISTATE_SEND_DATAIN
response state.

This ends up preventing memory release of StatSN acknowledged commands
in a timely manner when under heavy large block streaming DATAIN
workloads.

The regression bug was initially introduced with:

commit 6f3c0e69a9c20441bdc6d3b2d18b83b244384ec6
Author: Andy Grover <agrover@redhat.com>
Date: Tue Apr 3 15:51:09 2012 -0700

target/iscsi: Refactor target_tx_thread immediate+response queue loops

Go ahead and follow original iscsi_target_tx_thread() logic and check
to break for immediate queue processing after each DataIN Sequence and/or
Response PDU has been sent.

Reported-by: Benjamin ESTRABAUD <be@mpstor.com>
Cc: Andy Grover <agrover@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
drivers/target/iscsi/iscsi_target.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/target/iscsi/iscsi_target.c b/drivers/target/iscsi/iscsi_target.c
index ac41f04..3e7ac0c 100644
--- a/drivers/target/iscsi/iscsi_target.c
+++ b/drivers/target/iscsi/iscsi_target.c
@@ -3608,6 +3608,10 @@ check_rsp_state:
spin_lock_bh(&cmd->istate_lock);
cmd->i_state = ISTATE_SENT_STATUS;
spin_unlock_bh(&cmd->istate_lock);
+
+ if (atomic_read(&conn->check_immediate_queue))
+ return 1;
+
continue;
} else if (ret == 2) {
/* Still must send status,
@@ -3697,7 +3701,7 @@ check_rsp_state:
}

if (atomic_read(&conn->check_immediate_queue))
- break;
+ return 1;
}

return 0;
@@ -3741,12 +3745,15 @@ restart:
signal_pending(current))
goto transport_err;

+get_immediate:
ret = handle_immediate_queue(conn);
if (ret < 0)
goto transport_err;

ret = handle_response_queue(conn);
- if (ret == -EAGAIN)
+ if (ret == 1)
+ goto get_immediate;
+ else if (ret == -EAGAIN)
goto restart;
else if (ret < 0)
goto transport_err;
--
1.8.1.2


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