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[209.85.167.46]) by smtp.gmail.com with ESMTPSA id b23-20020a05651c033700b00247eb53f798sm1081572ljp.140.2022.03.18.11.56.21 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 18 Mar 2022 11:56:21 -0700 (PDT) Received: by mail-lf1-f46.google.com with SMTP id m3so3519114lfj.11 for ; Fri, 18 Mar 2022 11:56:21 -0700 (PDT) X-Received: by 2002:a05:6512:2037:b0:448:92de:21de with SMTP id s23-20020a056512203700b0044892de21demr6661516lfs.52.1647629780934; Fri, 18 Mar 2022 11:56:20 -0700 (PDT) MIME-Version: 1.0 References: <20220318131600.iv7ct2m4o52plkhl@quack3.lan> In-Reply-To: <20220318131600.iv7ct2m4o52plkhl@quack3.lan> From: Linus Torvalds Date: Fri, 18 Mar 2022 11:56:04 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: writeback completion soft lockup BUG in folio_wake_bit() To: Jan Kara Cc: Matthew Wilcox , Brian Foster , Linux-MM , linux-fsdevel , linux-xfs , Hugh Dickins , Namjae Jeon , Ashish Sangwan , "Theodore Ts'o" , Ext4 Developers List Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 4EFB4A0019 X-Stat-Signature: g3nnfqcdshf9p3hsa7dady6hio636u3k Authentication-Results: imf15.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=google header.b="f7MfvhR/"; dmarc=none; spf=pass (imf15.hostedemail.com: domain of torvalds@linuxfoundation.org designates 209.85.167.43 as permitted sender) smtp.mailfrom=torvalds@linuxfoundation.org X-Rspam-User: X-HE-Tag: 1647629784-614798 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 Fri, Mar 18, 2022 at 6:16 AM Jan Kara wrote: > > I agree with Dave that 'keep_towrite' thing is kind of self-inflicted > damage on the ext4 side (we need to write out some blocks underlying the > page but cannot write all from the transaction commit code, so we need to > keep xarray tags intact so that data integrity sync cannot miss the page). > Also it is no longer needed in the current default ext4 setup. But if you > have blocksize < pagesize and mount the fs with 'dioreadlock,data=ordered' > mount options, the hack is still needed AFAIK and we don't have a > reasonable way around it. I assume you meant 'dioread_lock'. Which seems to be the default (even if 'data=ordered' is not). Anyway - if it's not a problem for any current default setting, maybe the solution is to warn about this case and turn it off? IOW, we could simply warn about "data=ordered is no longer supported" and turn it into data=journal. Obviously *only* do this for the case of "blocksize < PAGE_SIZE". If this ext4 thing is (a) obsolete and (b) causes VFS-level problems that nobody else has, I really think we'd be much better off disabling it than trying to work with it. Linus