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AJvYcCWUuW2Nef5sT4pItUlyIDZS7r5EnVYJeWJPqQf8ok4RyKGbaB+COGMOP29UEUCPp55gGXNcswqUxg==@kvack.org X-Gm-Message-State: AOJu0YzfdZYiAEOczAbDToslHelbE8W/7NmxlaS2BSas2MCSOA2+uxj6 17fkJGExMn2NLZfFUzBPjXfFwxvxT3hdm+2qqjwMNADGGSDDK2y+nzYl0GgYHjlXY0K25bYaDaM uebsyEGT7y/VVznEjM2YzDkF6JsHDW9c1dP6Vm2M= X-Gm-Gg: ASbGnct8afLt7diw7GOA2RR0Fjf1IqdtyFrf/mlUgmGSPVpS0yi+jclWwgJPU4QFTj/ ELfJvaeqVrWP8R/N4tO4gRov4MSyB9Y31j/hGUYxrpxF/E23dRcat0eBNnLNzwrLcwOU0jcafo1 HtcjzzOojSnftJ2nexztInj+8hgbnQaZ48PP1R4QsRMURYJ3RtqdKPsVgxmeas9vt+u+i7jie0l dkYysIOPJiSuIViLmjPirGLlgb8POfR9rjWz74F2BvYML73oHoetENc6yYcNBpZkYDGtA== X-Google-Smtp-Source: AGHT+IG+lg4eS5i0rptnxHqewOGmi9WIWtm3BkNS150hRV68edD3IKYERtGEqWDxSOmk7U8Kg75UXfI9iTTk7B7cmnk= X-Received: by 2002:a05:622a:1aa3:b0:4eb:a0aa:28e with SMTP id d75a77b69052e-4ee58936cb6mr772331cf.64.1763673645433; Thu, 20 Nov 2025 13:20:45 -0800 (PST) MIME-Version: 1.0 References: <20251120184211.2379439-1-joannelkoong@gmail.com> <20251120184211.2379439-3-joannelkoong@gmail.com> <5c1630ac-d304-4854-9ba6-5c9cc1f78be5@kernel.org> In-Reply-To: <5c1630ac-d304-4854-9ba6-5c9cc1f78be5@kernel.org> From: Joanne Koong Date: Thu, 20 Nov 2025 13:20:33 -0800 X-Gm-Features: AWmQ_bknxKe3HYjwzzfUFST-_e4QC_Zgx5EeYqCXoRNHcbarFlFOQ1yJzG1WvYc Message-ID: Subject: Re: [PATCH v1 2/2] fs/writeback: skip inodes with potential writeback hang in wait_sb_inodes() To: "David Hildenbrand (Red Hat)" Cc: akpm@linux-foundation.org, linux-mm@kvack.org, shakeel.butt@linux.dev, athul.krishna.kr@protonmail.com, miklos@szeredi.hu, stable@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: jmzkzdfkgafg9j6d5fdw1krpsnhsh3fj X-Rspam-User: X-Rspamd-Queue-Id: 0985316000F X-Rspamd-Server: rspam10 X-HE-Tag: 1763674047-748706 X-HE-Meta: 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 9+YKlU26 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 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: List-Subscribe: List-Unsubscribe: On Thu, Nov 20, 2025 at 12:23=E2=80=AFPM David Hildenbrand (Red Hat) wrote: > > On 11/20/25 19:42, Joanne Koong wrote: > > During superblock writeback waiting, skip inodes where writeback may > > take an indefinite amount of time or hang, as denoted by the > > AS_WRITEBACK_MAY_HANG mapping flag. > > > > Currently, fuse is the only filesystem with this flag set. For a > > properly functioning fuse server, writeback requests are completed and > > there is no issue. However, if there is a bug in the fuse server and it > > hangs on writeback, then without this change, wait_sb_inodes() will wai= t > > forever. > > > > Signed-off-by: Joanne Koong > > Fixes: 0c58a97f919c ("fuse: remove tmp folio for writebacks and interna= l rb tree") > > Reported-by: Athul Krishna > > --- > > fs/fs-writeback.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c > > index 2b35e80037fe..eb246e9fbf3d 100644 > > --- a/fs/fs-writeback.c > > +++ b/fs/fs-writeback.c > > @@ -2733,6 +2733,9 @@ static void wait_sb_inodes(struct super_block *sb= ) > > if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK)) > > continue; > > > > + if (mapping_writeback_may_hang(mapping)) > > + continue; > > I think I raised it in the past, but simply because it could happen, why > would we unconditionally want to do that for all fuse mounts? That just > seems wrong :( I think it's considered a userspace regression if we don't revert the program behavior back to its previous version, even if it is from the program being incorrectly written, as per the conversation in [1]. [1] https://lore.kernel.org/regressions/CAJnrk1Yh4GtF-wxWo_2ffbr90R44u0WDmM= AEn9vr9pFgU0Nc6w@mail.gmail.com/T/#m73cf4b4828d51553caad3209a5ac92bca78e15d= 2 > > To phrase it in a different way, if any writeback could theoretically > hang, why are we even waiting on writeback in the first place? > I think it's because on other filesystems, something has to go seriously wrong for writeback to hang, but on fuse a server can easily make writeback hang and as it turns out, there are already existing userspace programs that do this accidentally. Thanks, Joanne > -- > Cheers > > David