makemkvcon hangs at 100% CPU after drive identification – LG GGC-H20L (fw 1.03)

[lavalaugh]

Hi,

MakeMKV hangs indefinitely when scanning a disc in my LG GGC-H20L. The GUI stays on "Loading..." forever and makemkvcon never gets past the startup messages. This happens with both my own build of v2.0.0 (built from source per the Linux forum guide) and the Flathub package.

System
- Debian 13, kernel 6.12.113+deb13-amd64, x86_64
- MakeMKV v2.0.0 linux(x64-release)
- Drive: HL-DT-ST BDDVDRW GGC-H20L, firmware 1.03 (2008-09-18), connected via SATA
- Drive region: RPC2, region 2 set
- Tested with multiple region 2 DVDs (UDF 1.02), a region 1 DVD and a Blu-ray, same result on all discs

Symptoms
- If a disc is in the drive when MakeMKV starts, MakeMKV freezes on Scanning drive.
- If I start MakeMKV with an empty drive and then insert a disc, the drive appears (Drive Information and LibreDrive "Possible, might be supported" are shown), but the disc stays on "Loading..." forever
- makemkvcon -r --debug info disc:0 prints the startup messages and the DEBUG Code 0 line, then nothing

What I've checked
- Kernel/hardware: no ATA errors in dmesg; dd from /dev/sr0 reads fine at ~4.3 MB/s
- Permissions: /dev/sr0 and /dev/sg0 accessible, no other process holding the drive
- strace: all SG_IO commands complete within milliseconds. The two READ BUFFER (3C 06) probes get ILLEGAL REQUEST / Invalid field in CDB, then 3C 05 succeeds. The last file access is an open of ~/.libdriveio/sdf.conf (ENOENT). After that there's no further drive I/O
- top: one thread sits at ~100% CPU indefinitely while all other threads wait on futexes
- Internet access disabled in Preferences: same hang, so it isn't caused by downloaded data
- Same hang regardless of disc type (DVD and Blu-ray), which points to the drive handling rather than the disc

Backtrace of the busy thread (LWP 7063, the only one not in libc).
Binary load base: 0x55d549c76000 (/usr/bin/makemkvcon), offsets in brackets:
#0 0x000055d54a2929a5 in ?? () [+0x61c9a5]
#1 0x000055d54a28ddd5 in ?? () [+0x617dd5]
#2 0x000055d54a1e1a5f in ?? () [+0x56ba5f]
#3 0x000055d54a2f4f6b in ?? () [+0x67ef6b]
#4 0x000055d54a2f37f8 in ?? () [+0x67d7f8]
#5 0x000055d54a2052e0 in ?? () [+0x58f2e0]
#6 0x000055d54a1e0019 in ?? () [+0x56a019]
#7 0x000055d54a308bf8 in ?? () [+0x692bf8]
#8 0x000055d54a309827 in ?? () [+0x693827]

The full debug log and the complete gdb backtrace (all threads) are attached.

It looks like a busy loop somewhere after the LibreDrive probe / SDF lookup for this drive.

Thanks!

[lavalaugh]

Update: I found a workaround that points to an initialization issue.

If I connect a USB DVD drive, let MakeMKV load a disc in it (no ripping), and then disconnect the USB drive, the GGC-H20L works normally for the rest of that MakeMKV session. After restarting MakeMKV the hang is back, so the state that "fixes" it only lives inside the running process.

No files are created or changed during this (only screen.conf on exit), so it's not missing on-disk data. It looks like a successful scan on another drive initializes something internally that the GGC-H20L code path depends on but doesn't set up by itself.

Just connecting the USB drive without a disc doesn't help. A disc has to be fully loaded/scanned on it before the GGC-H20L starts working.