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    Subject[PATCH 4.2.y-ckt 177/268] iscsi-target: Fix potential dead-lock during node acl delete
    Date
    4.2.8-ckt3 -stable review patch.  If anyone has any objections, please let me know.

    ---8<------------------------------------------------------------

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

    commit 26a99c19f810b2593410899a5b304b21b47428a6 upstream.

    This patch is a iscsi-target specific bug-fix for a dead-lock
    that can occur during explicit struct se_node_acl->acl_group
    se_session deletion via configfs rmdir(2), when iscsi-target
    time2retain timer is still active.

    It changes iscsi-target to obtain se_portal_group->session_lock
    internally using spin_in_locked() to check for the specific
    se_node_acl configfs shutdown rmdir(2) case.

    Note this patch is intended for stable, and the subsequent
    v4.5-rc patch converts target_core_tpg.c to use proper
    se_sess->sess_kref reference counting for both se_node_acl
    deletion + se_node_acl->queue_depth se_session restart.

    Reported-by:: Sagi Grimberg <sagig@mellanox.com>
    Cc: Christoph Hellwig <hch@lst.de>
    Cc: Hannes Reinecke <hare@suse.de>
    Cc: Andy Grover <agrover@redhat.com>
    Cc: Mike Christie <michaelc@cs.wisc.edu>
    Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
    Signed-off-by: Kamal Mostafa <kamal@canonical.com>
    ---
    drivers/target/iscsi/iscsi_target_configfs.c | 16 +++++++++++++++-
    1 file changed, 15 insertions(+), 1 deletion(-)

    diff --git a/drivers/target/iscsi/iscsi_target_configfs.c b/drivers/target/iscsi/iscsi_target_configfs.c
    index db3b9b9..a13d59e 100644
    --- a/drivers/target/iscsi/iscsi_target_configfs.c
    +++ b/drivers/target/iscsi/iscsi_target_configfs.c
    @@ -1834,7 +1834,8 @@ static int lio_tpg_check_prot_fabric_only(
    }

    /*
    - * Called with spin_lock_bh(struct se_portal_group->session_lock) held..
    + * Called with spin_lock_irq(struct se_portal_group->session_lock) held
    + * or not held.
    *
    * Also, this function calls iscsit_inc_session_usage_count() on the
    * struct iscsi_session in question.
    @@ -1842,19 +1843,32 @@ static int lio_tpg_check_prot_fabric_only(
    static int lio_tpg_shutdown_session(struct se_session *se_sess)
    {
    struct iscsi_session *sess = se_sess->fabric_sess_ptr;
    + struct se_portal_group *se_tpg = se_sess->se_tpg;
    + bool local_lock = false;
    +
    + if (!spin_is_locked(&se_tpg->session_lock)) {
    + spin_lock_irq(&se_tpg->session_lock);
    + local_lock = true;
    + }

    spin_lock(&sess->conn_lock);
    if (atomic_read(&sess->session_fall_back_to_erl0) ||
    atomic_read(&sess->session_logout) ||
    (sess->time2retain_timer_flags & ISCSI_TF_EXPIRED)) {
    spin_unlock(&sess->conn_lock);
    + if (local_lock)
    + spin_unlock_irq(&sess->conn_lock);
    return 0;
    }
    atomic_set(&sess->session_reinstatement, 1);
    spin_unlock(&sess->conn_lock);

    iscsit_stop_time2retain_timer(sess);
    + spin_unlock_irq(&se_tpg->session_lock);
    +
    iscsit_stop_session(sess, 1, 1);
    + if (!local_lock)
    + spin_lock_irq(&se_tpg->session_lock);

    return 1;
    }
    --
    1.9.1
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