OK, it turned out that said colleague wasn’t responsible at all. Turns out, the real trigger was me creating a new volume on our SAN, on the same array that houses the OCFS2 volume.

Apparently, during creation of an additional SAN volume, all other SAN volumes in this array are either read-only or delayed during that time, as you can see from the following log:

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kernel: (13,3):o2hb_write_timeout:242 ERROR: Heartbeat write timeout to device sdd1 after 12000 milliseconds
kernel: Heartbeat thread (13) printing last 24 blocking operations (cur = 4):
kernel: Heartbeat thread stuck at waiting for read completion, stuffing current time into that blocker (index 4)
kernel: Index 5: took 0 ms to do submit_bio for read
kernel: Index 6: took 0 ms to do waiting for read completion
kernel: Index 7: took 0 ms to do bio alloc write
kernel: Index 8: took 0 ms to do bio add page write
kernel: Index 9: took 0 ms to do submit_bio for write
kernel: Index 10: took 0 ms to do checking slots
kernel: Index 11: took 0 ms to do waiting for write completion
kernel: Index 12: took 2002 ms to do msleep
kernel: Index 13: took 0 ms to do allocating bios for read
kernel: Index 14: took 0 ms to do bio alloc read
kernel: Index 15: took 0 ms to do bio add page read
kernel: Index 16: took 0 ms to do submit_bio for read
kernel: Index 17: took 0 ms to do waiting for read completion
kernel: Index 18: took 0 ms to do bio alloc write
kernel: Index 19: took 0 ms to do bio add page write
kernel: Index 20: took 0 ms to do submit_bio for write
kernel: Index 21: took 0 ms to do checking slots
kernel: Index 22: took 0 ms to do waiting for write completion
kernel: Index 23: took 2004 ms to do msleep
kernel: Index 0: took 0 ms to do allocating bios for read
kernel: Index 1: took 0 ms to do bio alloc read
kernel: Index 2: took 0 ms to do bio add page read
kernel: Index 3: took 0 ms to do submit_bio for read
kernel: Index 4: took 9995 ms to do waiting for read completion
kernel: (13,3):o2hb_stop_all_regions:1682 ERROR: stopping heartbeat on all active regions.
kernel: Kernel panic - not syncing: *** ocfs2 is very sorry to be fencing this system by panicing ***