I think I'm hitting a hang in rsync. I'm using rev c0d07c098724ee8c382a498cab991f7d8467d778 in the b3.0.x branch.

The command is:
rsync -raHx --stats --inplace --no-whole-file --delete /xback2_back1/home_rcr36/20110707-000502/ /mnt/btrfs/home_rcr36/current/

Where both file systems are local. Running strace on the process shows no activity. The hanging process is the rsync with the lowest PID.

I attached gdb to the hanging rsync. Here is the back trace:

0x000000000041e5c4 in hash_search (f=4, s=0xcc1ec0, buf=0xcc1ef0, len=2000967340) at match.c:211
211                             if (updating_basis_file && s->sums[i].offset < offset

(gdb) back
#0  0x000000000041e5c4 in hash_search (f=4, s=0xcc1ec0, buf=0xcc1ef0, len=2000967340) at match.c:211
#1  match_sums (f=4, s=0xcc1ec0, buf=0xcc1ef0, len=2000967340) at match.c:369
#2  0x0000000000414491 in send_files (f_in=5, f_out=4) at sender.c:337
#3  0x000000000041cd96 in client_run (f_in=5, f_out=4, pid=15684, argc=1, argv=0xcac240) at main.c:1039
#4  0x000000000041d455 in start_client (argc=2, argv=0xcac240) at main.c:1287
#5  main (argc=2, argv=0xcac240) at main.c:1514

The system is Fedora Linux 14 x86-64. I continued the program and reattached the debugger. It was stuck in the same place.