scsi: iscsi: iscsi_tcp: Avoid holding spinlock while calling getpeername()

The kernel may fail to boot or devices may fail to come up when
initializing iscsi_tcp devices starting with Linux 5.8.

Commit a79af8a6 ("[SCSI] iscsi_tcp: use iscsi_conn_get_addr_param
libiscsi function") introduced getpeername() within the session spinlock.

Commit 1b66d253 ("bpf: Add get{peer, sock}name attach types for
sock_addr") introduced BPF_CGROUP_RUN_SA_PROG_LOCK() within getpeername(),
which acquires a mutex and when used from iscsi_tcp devices can now lead to
"BUG: scheduling while atomic:" and subsequent damage.

Ensure that the spinlock is released before calling getpeername() or
getsockname(). sock_hold() and sock_put() are used to ensure that the
socket reference is preserved until after the getpeername() or
getsockname() complete.

Link: https://bugzilla.redhat.com/show_bug.cgi?id=1877345
Link: https://lkml.org/lkml/2020/7/28/1085
Link: https://lkml.org/lkml/2020/8/31/459
Link: https://lore.kernel.org/r/20200928043329.606781-1-mark.mielke@gmail.com


Fixes: a79af8a6 ("[SCSI] iscsi_tcp: use iscsi_conn_get_addr_param libiscsi function")
Fixes: 1b66d253 ("bpf: Add get{peer, sock}name attach types for sock_addr")
Cc: stable@vger.kernel.org
Reported-by: Marc Dionne <marc.c.dionne@gmail.com>
Tested-by: Marc Dionne <marc.c.dionne@gmail.com>
Reviewed-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Mark Mielke <mark.mielke@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>