From: Khazhismel Kumykov Subject: Re: [PATCH] ext4: Return EIO on read error in ext4_find_entry Date: Fri, 23 Jun 2017 15:33:46 -0700 Message-ID: References: <20170622232307.48392-1-khazhy@google.com> <20170623044314.7f23ighkelnpgnah@thunk.org> <204110E6-EECE-4925-9020-EC6D9633C822@dilger.ca> <20170623122603.jmvyw4oqkojcapv3@thunk.org> Mime-Version: 1.0 Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-256; boundary="94eb2c043d4ed9eb8f0552a831dc" Cc: "Theodore Ts'o" , adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org To: Andreas Dilger Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org --94eb2c043d4ed9eb8f0552a831dc Content-Type: text/plain; charset="UTF-8" On Fri, Jun 23, 2017 at 2:36 PM, Andreas Dilger wrote: > On Jun 23, 2017, at 6:26 AM, Theodore Ts'o wrote: >> >> The problem is that if we continue, successive reads may all take >> seconds or minutes to fail, thus tieing up the process for a long >> time. > > Sorry, I don't understand where the seconds or minutes of delay come from? > Is that because of long SCSI retries in the block layer, or in the disk > itself, or something caused specifically because of this code? For a networked block device we may be retrying for a while before giving up, although this also applies to the initial failed read. > >> By returning EIO right away, we can "fast fail". > > But it seems like you don't necessarily need to fail at all? Something like the > following would return an error if the entry is not found, but still search the > rest of the leaf blocks (if any) before giving up: > Giving up early or checking future blocks both work, critical thing here is not returning NULL after seeing a read error. Previously to this the behavior was to continue to check future blocks after a read error, and it seemed OK. 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