BUG in mm/page-writeback.c:2652

[shankarapailoor]

Hi,

I am fuzzing linux 4.17-rc4 with BTRFS and I encountered a BUG in
mm/page-writeback.c error described below. This bug has occured 3
times in our fuzzing campaign.

Here is the full stack trace: https://pastebin.com/QcDi9xA2

Truncated Stack Trace: https://pastebin.com/GWRNmhmC

Here is a C reproducer: https://pastebin.com/xTAVB3L2

My linux configs: https://pastebin.com/6J1KMczH

It appears that there is a fault injection inside of create_io_em
during the slab allocation for the path. After that
extent_clear_unlock_delalloc gets called. I don't know if the
extent_map start and end are well defined in this case.

Regards,
Shankara Pailoor