This bug has been copied from bug #677703 and has been proposed to be backported to 5.6 z-stream (EUS).
in kernel-2.6.18-238.15.1.el5 linux-2.6-scsi-iscsi_tcp-fix-iscsi-s-sk_user_data-access.patch
Technical note added. If any revisions are required, please edit the "Technical Notes" field accordingly. All revisions will be proofread by the Engineering Content Services team. New Contents: Running a reboot test on an iSCSI root host resulted in kernel panic. When the iscsi_tcp module is destroying a connection it grabs the sk_callback_lock and clears the sk_user_data/conn pointer to signal that the callback functions should not execute the operation. However, some functions were not grabbing the lock, causing a NULL pointer kernel panic when iscsi_sw_tcp_conn_restore_callbacks was called and, consequently, one of the callbacks was called. With this update, the underlying source code has been modified to address this issue, and kernel panic no longer occurs.
An advisory has been issued which should help the problem described in this bug report. This report is therefore being closed with a resolution of ERRATA. For more information on therefore solution and/or where to find the updated files, please follow the link below. You may reopen this bug report if the solution does not work for you. http://rhn.redhat.com/errata/RHSA-2011-0927.html