[bug report] scsi: qla2xxx: Fix SRB leak on switch command timeout

[Dan Carpenter <dan.carpenter@xxxxxxxxxx>]

Hello Quinn Tran,

The patch af2a0c51b120: "scsi: qla2xxx: Fix SRB leak on switch
command timeout" from Nov 5, 2019, leads to the following static
checker warning:

	drivers/scsi/qla2xxx/qla_os.c:1032 qla2xxx_mqueuecommand()
	error: dereferencing freed memory 'sp'

drivers/scsi/qla2xxx/qla_os.c
  1020  
  1021          return 0;
  1022  
  1023  qc24_host_busy_free_sp:
  1024          sp->free(sp);
  1025  
  1026  qc24_target_busy:
  1027          return SCSI_MLQUEUE_TARGET_BUSY;
  1028  
  1029  qc24_free_sp_fail_command:
  1030          sp->free(sp);
  1031          CMD_SP(cmd) = NULL;
  1032          qla2xxx_rel_qpair_sp(sp->qpair, sp);

This seems like potentially a false positive but the code is weird.
In this case we know that ->free is qla2xxx_qpair_sp_free_dma().

Smatch isn't making that connection and it complains that half the
free functions call qla2xxx_rel_qpair_sp() and half don't.  These three
free "sp"

qla2x00_sp_free()
qla2x00_els_dcmd_sp_free()
qla2x00_bsg_sp_free()

The free functions which don't free "sp" are:

qla2x00_sp_free_dma()
qla2xxx_qpair_sp_free_dma()
qla2xxx_rel_free_warning()

  1033  
  1034  qc24_fail_command:
  1035          cmd->scsi_done(cmd);
  1036  
  1037          return 0;
  1038  }

regards,
dan carpenter