File system becomes read only spontaneously

[mk01]

@all

the remount to RO is only possibility to avoid reflash. BTRFS remounts to RO if data/metadata being processed do not match, metadata tree looks broken etc. this can have many reasons, mostly it is poor AC, too much OC (in rare case also older kernel, like pre 3.12.x). if filesystem would continue W operations with wrong informations, it would become unreadable completely very soon.

if the problem is just OC or spikes in poor AC, then just reboot is enough. if FS is really damaged, then RO will return 30s-1m after boot. in that case reboot to initramfs and "btrfs check" could help (btrfs-tools at minimum 3.14 version - otherwise reformat).