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[109.42.2.46]) by smtp.gmail.com with ESMTPSA id x5sm23142789wrg.69.2019.09.09.21.21.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 09 Sep 2019 21:21:17 -0700 (PDT) Date: Tue, 10 Sep 2019 06:21:07 +0200 From: "Ahmed S. Darwish" To: Theodore Ts'o , Andreas Dilger , Linus Torvalds Cc: Jan Kara , zhangjs , linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: Linux 5.3-rc8 Message-ID: <20190910042107.GA1517@darwi-home-pc> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.12.1 (2019-06-15) Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org Hi, On Sun, Sep 08, 2019 at 01:59:27PM -0700, Linus Torvalds wrote: > So we probably didn't strictly need an rc8 this release, but with LPC > and the KS conference travel this upcoming week it just makes > everything easier. > The commit b03755ad6f33 (ext4: make __ext4_get_inode_loc plug), [1] which was merged in v5.3-rc1, *always* leads to a blocked boot on my system due to low entropy. The hardware is not a VM: it's a Thinkpad E480 (i5-8250U CPU), with a standard Arch user-space. It was discovered through bisecting the problem v5.2 => v5.3-rc1, since v5.2 never had any similar issues. The issue still persists in v5.3-rc8: reverting that commit always fixes the problem. It seems that batching the directory lookup I/O requests (which are possibly a lot during boot) is minimizing sources of disk-activity- induced entropy? [2] [3] Can this even be considered a user-space breakage? I'm honestly not sure. On my modern RDRAND-capable x86, just running rng-tools rngd(8) early-on fixes the problem. I'm not sure about the status of older CPUs though. Thanks, [1] commit b03755ad6f33b7b8cd7312a3596a2dbf496de6e7 Author: zhangjs Date: Wed Jun 19 23:41:29 2019 -0400 ext4: make __ext4_get_inode_loc plug Add a blk_plug to prevent the inode table readahead from being submitted as small I/O requests. Signed-off-by: zhangjs Signed-off-by: Theodore Ts'o Reviewed-by: Jan Kara [2] https://lkml.kernel.org/r/20190619122457.GF27954@quack2.suse.cz [3] block/blk-core.c :: blk_start_plug() -- darwi http://darwish.chasingpointers.com