Hi

Today I found a crash when adding code for the poll ring to my implementation.
Kernel is 2b58a38ef46e91edd68eec58bdb817c42474cad6

Here's how to reproduce:

code at
https://github.com/glommer/seastar.git branch poll-ring

1. same as previous steps to configure seastar, but compile with:
ninja -C build/release apps/io_tester/io_tester

2. Download the yaml file attached

3. Run with:

./build/release/apps/io_tester/io_tester --conf ~/test.yaml --duration
15 --directory /var/disk1  --reactor-backend=uring --smp 1

(directory must be on xfs because we do c++ but we're not savages)