I’ve been testing the updated sdhost driver and just experienced a case of write errors (?) to the disk resulting in the file system switching to read only mode - possibly the same thing that happened to me during the jenkins build except this time I was logged in via ssh already so I was able to gather some debug logs.
At the time it happened I was using dd to create large files on both / and /boot to test how our update system responds to low disk space - on the /boot partition I accidentally specified a size bigger than the available free space, although that may not have been a factor. Here is the log file:
This is on my same samsung 32GB card which requires the cmd23quirk workaround to avoid hangs. (Eg the latest kernels that have removed cmd23 quirk by default cause random disk IO freezes on this card - I either have to use sdhost or bcm2835_mmc.mmc_debug=0x2000 in cmdline.txt to re-enable cmd23 quirk be able to use this card)