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Date:   Thu, 22 Jun 2023 09:39:19 +0200
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Subject: Re: [PATCH v1] erofs: Fix detection of atomic context
To:     Sandeep Dhavale <dhavale@google.com>, Gao Xiang <xiang@kernel.org>,
        Chao Yu <chao@kernel.org>, Yue Hu <huyue2@coolpad.com>,
        Jeffle Xu <jefflexu@linux.alibaba.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>
Cc:     Will Shiu <Will.Shiu@mediatek.com>, kernel-team@android.com,
        linux-erofs@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org
References: <20230621220848.3379029-1-dhavale@google.com>
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From:   Alexandre Mergnat <amergnat@baylibre.com>
In-Reply-To: <20230621220848.3379029-1-dhavale@google.com>
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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@baylibre.com>

-- 
Regards,
Alexandre