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[209.85.220.65]) by mx.google.com with SMTPS id i4sor3071133wrx.38.2019.02.09.05.52.34 for (Google Transport Security); Sat, 09 Feb 2019 05:52:34 -0800 (PST) Received-SPF: pass (google.com: domain of righi.andrea@gmail.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=ho854t0V; spf=pass (google.com: domain of righi.andrea@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=righi.andrea@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=a1FxRbJ08wKgp4Co0znQWeKyAEWRpt3r5CDQgl/lzA4=; b=ho854t0VeE6vkAj0xsMCBVg+GmgJHVfw5OjfuHOJNNggl2sV7EERA8YSfPVlbMvOI/ 8VfPfvbCOdKdg1UTWHM/i0jDat3tgSYv0ewqUWVbUABw4sOc26cXz78V1kDZdl0FeXcU fUUbDB73SdMwb9ZQit//tkf/yJmMy+BsmPYc5egWKEuM9+cJW5rYCz/vmSeWAyyx8Fsk hc27LyFIpXFFNT7f/0lYIbAdpujM488pot5HUf31+3kyX5gkm3JvloV91OtiSEWmXl4a S+ls75NLMEcJxwYPKh92JNiCRLHdMp4QjFpU7eGPGle1WxcJM7BvMOUeEOWjSkya9ZGO 1TGw== X-Google-Smtp-Source: AHgI3IYCGgyeMoumNCNf/hlgXlYmgnGoCIA2EAC1vCyg+s6hZ7Scw34UnmRgzD6RTx7omoGjVtJXAw== X-Received: by 2002:adf:9004:: with SMTP id h4mr13476386wrh.121.1549720353621; Sat, 09 Feb 2019 05:52:33 -0800 (PST) Received: from localhost ([95.238.120.247]) by smtp.gmail.com with ESMTPSA id r12sm6648362wrt.76.2019.02.09.05.52.32 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sat, 09 Feb 2019 05:52:32 -0800 (PST) Date: Sat, 9 Feb 2019 14:52:31 +0100 From: Andrea Righi To: Josef Bacik Cc: Paolo Valente , Tejun Heo , Li Zefan , Johannes Weiner , Jens Axboe , Vivek Goyal , Dennis Zhou , cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH] blkcg: prevent priority inversion problem during sync() Message-ID: <20190209135231.GA1910@xps-13> References: <20190209120633.GA2506@xps-13> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190209120633.GA2506@xps-13> User-Agent: Mutt/1.9.4 (2018-02-28) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sat, Feb 09, 2019 at 01:06:33PM +0100, Andrea Righi wrote: ... > +/** > + * blkcg_wb_waiters_on_bdi - check for writeback waiters on a block device > + * @bdi: block device to check > + * > + * Return true if any other blkcg is waiting for writeback on the target block > + * device, false otherwise. > + */ > +bool blkcg_wb_waiters_on_bdi(struct backing_dev_info *bdi) > +{ > + struct blkcg *blkcg, *curr_blkcg; > + bool ret = false; > + > + if (unlikely(!bdi)) > + return false; > + > + rcu_read_lock(); > + curr_blkcg = css_to_blkcg(task_css(current, io_cgrp_id)); Sorry, the logic is messed up here. We shouldn't get curr_blkcg from the current task, because during writeback throttling the context is obviously not the current task. I'll post a new patch soon. > + list_for_each_entry_rcu(blkcg, &bdi->cgwb_waiters, cgwb_wait_node) > + if (blkcg != curr_blkcg) { > + ret = true; > + break; > + } > + rcu_read_unlock(); > + > + return ret; > +} -Andrea