While handling an I/O completion for the compare portion of a
COMPARE_AND_WRITE command, it may happen that the
compare_and_write_callback function submits new bio structs while still in
softirq context.

Low level drivers like md raid5 do not expect their make_request call to be
used in softirq context, they call into schedule() and create a deadlocked
system.

 __schedule at ffffffff873a0807
 schedule at ffffffff873a0cc5
 raid5_get_active_stripe at ffffffffc0875744 [raid456]
 raid5_make_request at ffffffffc0875a50 [raid456]
 md_handle_request at ffffffff8713b9f9
 md_make_request at ffffffff8713bacb
 generic_make_request at ffffffff86e6f14b
 submit_bio at ffffffff86e6f27c
 iblock_submit_bios at ffffffffc0b4e4dc [target_core_iblock]
 iblock_execute_rw at ffffffffc0b4f3ce [target_core_iblock]
 __target_execute_cmd at ffffffffc1090079 [target_core_mod]
 compare_and_write_callback at ffffffffc1093602 [target_core_mod]
 target_cmd_interrupted at ffffffffc108d1ec [target_core_mod]
 target_complete_cmd_with_sense at ffffffffc108d27c [target_core_mod]
 iblock_complete_cmd at ffffffffc0b4e23a [target_core_iblock]
 dm_io_dec_pending at ffffffffc00db29e [dm_mod]
 clone_endio at ffffffffc00dbf07 [dm_mod]
 raid5_align_endio at ffffffffc086d6c2 [raid456]
 blk_update_request at ffffffff86e6d950
 scsi_end_request at ffffffff87063d48
 scsi_io_completion at ffffffff87063ee8
 blk_complete_reqs at ffffffff86e77b05
 __softirqentry_text_start at ffffffff876000d7

This problem appears to be an issue between target_cmd_interrupted() and
compare_and_write_callback(). target_cmd_interrupted() calls the se_cmd's
transport_complete_callback function pointer if the se_cmd is being stopped
or aborted, and CMD_T_ABORTED was set on the se_cmd.

When calling compare_and_write_callback(), the success parameter was set to
false. target_cmd_interrupted() seems to expect this means the callback
will do cleanup that does not require a process context. But
compare_and_write_callback() ignores the parameter if there was I/O done
for the compare part of COMPARE_AND_WRITE.

Since there was data, the function continued on, passed the compare, and
issued a write while ignoring the value of the success parameter.  The
submit of a bio for the write portion of the COMPARE_AND_WRITE then causes
schedule to be unsafely called from the softirq context.

Fix the bug in compare_and_write_callback by jumping to the out label if
success == "false", after checking if we have been called by
transport_generic_request_failure(); The command is being aborted or
stopped so there is no need to submit the write bio for the write part of
the COMPARE_AND_WRITE command.
Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
Link: https://lore.kernel.org/r/20221121092703.316489-1-mlombard@redhat.comReviewed-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>