ACK: [SRU][K/L][PATCH 0/1] fix cgroups v1 blkio.throttle statistics

[Tim Gardner]

On 5/8/23 11:18 PM, Andrea Righi wrote:
> BugLink: https://bugs.launchpad.net/bugs/2016186
> 
> [Impact]
> 
> Commit f382fb0bcef4 ("block: remove legacy IO schedulers") introduced a
> behavior change in the blkio throttle cgroup subsystem: IO statistics
> are not reported anymore unless a throttling rule is explicitly defined,
> because the current code only counts bios that are actually throttled.
> 
> This behavior change is potentially breaking some user-space
> applications that are relying on the old behavior (see original bug
> report).
> 
> [Test case]
> 
>   - mount cgroup v1
>   - create a blkio cgroup
>   - move a task into the blkio cgroup
>   - perform some I/O (i.e., dd)
>   - read the IO stats for the cgroup (blkio.throttle.io_serviced and
>     blkio.throttle.io_service_bytes in cgroupfs)
>   - IO stats are all 0, unless a throttle rule is defined
> 
> Previous behavior (kernel 5.15) was showing I/O statistics even without
> throttling rules defined.
> 
> [Fix]
> 
> Apply / backport this fix:
> https://lore.kernel.org/lkml/20230507170631.89607-1-hanjinke.666@bytedance.com/t/
> 
> [Regression potential]
> 
> The fix is affecting the block IO cgroup subsystem, we may see potential
> regressions in this particular cgroup subsystem with this fix applied.
> 
> [Additional notes]
> 
> This fix is provided as SAUCE patch for now, but it is likely to be
> applied to the upstream stable trees at this point (it has been
> submitted upstream and well tested).
> 
> 
Acked-by: Tim Gardner <tim.gardner at canonical.com>
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Tim Gardner
Canonical, Inc