Hi, I saw the same BUG from ide-cd on one of my systems.  I applied
the debugging patch to replace the BUG with blk_dump_rq_flags(), and I
got the output below (full boot log and .config attached to this
email).

Please let me know if there's anything else that would help debug the
problem.

[    4.072271] Uniform CD-ROM driver Revision: 3.20
[    4.098236] ide-cd: rq still having bio: dev hda: type=2, flags=114c8
[    4.100269]
[    4.100269] sector 1949759, nr/cnr 0/0
[    4.100269] bio ffff8102418cc600, biotail ffff8102418cc600, buffer 0000000000000000, d8
[    4.100269] cdb: 12 00 00 00 fe 00 00 00 00 00 00 00 00 00 00 00
[    4.101005] ide-cd: rq still having bio: dev hda: type=2, flags=114c8
[    4.104269]
[    4.104269] sector 1949759, nr/cnr 0/0
[    4.104269] bio ffff8102418cc600, biotail ffff8102418cc600, buffer 0000000000000000, d2
[    4.104269] cdb: 12 00 00 00 fe 00 00 00 00 00 00 00 00 00 00 00
[    4.109203] ide-cd: rq still having bio: dev hda: type=2, flags=114c8
[    4.112270]
[    4.112270] sector 1949759, nr/cnr 0/0
[    4.112270] bio ffff8102418cc600, biotail ffff8102418cc600, buffer 0000000000000000, d8
[    4.112270] cdb: 12 01 00 00 fe 00 00 00 00 00 00 00 00 00 00 00
[    4.112945] ide-cd: rq still having bio: dev hda: type=2, flags=114c8
[    4.116270]
[    4.116270] sector 1949759, nr/cnr 0/0
[    4.116270] bio ffff8102418cc600, biotail ffff8102418cc600, buffer 0000000000000000, d2
[    4.116270] cdb: 12 01 00 00 fe 00 00 00 00 00 00 00 00 00 00 00