Re: [PATCH v1] erofs: Fix detection of atomic context

[Alexandre Mergnat]

On 22/06/2023 00:08, Sandeep Dhavale wrote:
> Current check for atomic context is not sufficient as
> z_erofs_decompressqueue_endio can be called under rcu lock
> from blk_mq_flush_plug_list(). See the stacktrace [1]
>
> In such case we should hand off the decompression work for async
> processing rather than trying to do sync decompression in current
> context. Patch fixes the detection by checking for
> rcu_read_lock_any_held() and while at it use more appropriate
> !in_task() check than in_atomic().
>
> Background: Historically erofs would always schedule a kworker for
> decompression which would incur the scheduling cost regardless of
> the context. But z_erofs_decompressqueue_endio() may not always
> be in atomic context and we could actually benefit from doing the
> decompression in z_erofs_decompressqueue_endio() if we are in
> thread context, for example when running with dm-verity.
> This optimization was later added in patch [2] which has shown
> improvement in performance benchmarks.

Reviewed-by: Alexandre Mergnat <amergnat@xxxxxxxxxxxx>

--
Regards,
Alexandre