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AJvYcCXQ0n8HvsDT64v0I8YpWDlnlXapnQJ6PzDoMW+jU9CspX8T6fLZeIr2sdREwnJkIyb9o60Nas2CtJKAVJ/G@vger.kernel.org X-Gm-Message-State: AOJu0YxQthzB4J/AFgSRnvXLrm/x2gqDQ/facmm+JOAdf/6i9AshIUac MHqYR5aXhaSBjZkrTsxVpIQpgGYL8lClyuPLvTB7O/TG8R2r5vdiD9t2MqrAZdn3T1D/J3yZlgS uOm6MLkKpe6LwAwyI86KeDZbrcFhYik8= X-Gm-Gg: ATEYQzxbcNCS+ljDV907su9NzlJvt9jlnA4sWS90nr8kizLsudOKZiDjdYK9MMBIfbc nypIxsrHDASRlOuJ2HL2UQxA0yG2PvgZJAKzLyDG+Ax2afeiBdZJj6aoVU6hW6jGKgiVoL2Wnwe OM2ZGHVFK3YYeyqEfT9tF2QZz3aWlMmMIwGBsSlveATPjQyB8+00uD4m27kWjpppSBIR+zP4S4P owZta4NF8LMCC/NSmQVWdkozDbKgJn4GsO7y4AjMv/GA5TFDi+RYQYCDAGSMdppVG3AIukZtvRH MQWCmA== X-Received: by 2002:a05:600c:3495:b0:485:3b00:f939 with SMTP id 5b1f17b1804b1-486fedf6b7amr17160365e9.8.1773964531889; Thu, 19 Mar 2026 16:55:31 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20260319194540.3463371-1-joannelkoong@gmail.com> <20260319194540.3463371-2-joannelkoong@gmail.com> <1f1dafa7-54c7-4eae-a19e-5ec1be391079@kernel.org> In-Reply-To: <1f1dafa7-54c7-4eae-a19e-5ec1be391079@kernel.org> From: Joanne Koong Date: Thu, 19 Mar 2026 16:55:20 -0700 X-Gm-Features: AaiRm52BrVoXuXp1mgrMWHCIO62znYxeTnQ2oKGY6jvIBiTwB0i4w5xIYrFYXBI Message-ID: Subject: Re: [PATCH v2 1/1] writeback: don't block sync(2) for filesystems with no data integrity guarantees To: "David Hildenbrand (Arm)" Cc: brauner@kernel.org, linux-fsdevel@vger.kernel.org, jack@suse.cz, miklos@szeredi.hu, therealgraysky@proton.me, linux-pm@vger.kernel.org, stable@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, Mar 19, 2026 at 2:26=E2=80=AFPM David Hildenbrand (Arm) wrote: > > On 3/19/26 20:45, Joanne Koong wrote: > > Add a SB_I_NO_DATA_INTEGRITY superblock flag for filesystems that canno= t > > guarantee data persistence on sync (eg fuse). For superblocks with this > > flag set, sync(2) kicks off writeback of dirty inodes but does not wait > > for the flusher threads to complete the writeback. > > > > This replaces the per-inode AS_NO_DATA_INTEGRITY mapping flag added in > > commit f9a49aa302a0 ("fs/writeback: skip AS_NO_DATA_INTEGRITY mappings > > in wait_sb_inodes()"). The flag belongs at the superblock level because > > data integrity is a filesystem-wide property, not a per-inode one. > > Having this flag at the superblock level allows us to skip the logic in > > sync_inodes_sb() entirely, rather than iterating every dirty inode in > > wait_sb_inodes() only to skip each inode individually. > > Makes sense to me. > > [...] > > > if (sb->s_user_ns !=3D &init_user_ns) > > sb->s_iflags |=3D SB_I_UNTRUSTED_MOUNTER; > > sb->s_flags &=3D ~(SB_NOSEC | SB_I_VERSION); > > diff --git a/fs/sync.c b/fs/sync.c > > index 942a60cfedfb..aedbf723830a 100644 > > --- a/fs/sync.c > > +++ b/fs/sync.c > > @@ -73,7 +73,12 @@ EXPORT_SYMBOL(sync_filesystem); > > > > static void sync_inodes_one_sb(struct super_block *sb, void *arg) > > { > > - if (!sb_rdonly(sb)) > > + if (sb_rdonly(sb)) > > + return; > > + > > Should we move some of the comment you deleting over here? That's a good idea - I'll bring back the comment block that was previously in wait_sb_inodes() and move it here > > > + if (sb->s_iflags & SB_I_NO_DATA_INTEGRITY) > > + wakeup_flusher_threads_bdi(sb->s_bdi, WB_REASON_SYNC); > > + else > > sync_inodes_sb(sb); > > } > I was wondering whether that handling should be moved to > sync_inodes_sb(), so it would catch any (existing+future) callers. > > Alternatively, we could catch abuse by adding a warning to sync_inodes_sb= . Thinking about this some more, I think you're right. At the vfs layer, the only other relevant callers are generic_shutdown_super() when handling an unmount and syncfs for syncing a specific fd. For these, I was thinking it'd be more useful to return after writeback has actually completed, since the caller has to directly invoke the operation on a specific fd/mount. But that's wrong, we shouldn't be picking and choosing which syncs are ok vs not ok to wait for. And I'm realizing now there's also the hibernate/suspend call paths that call filesystems_freeze_callback() which can also call into sync_filesystem() -> sync_inodes_sb()... I'll make this change for v3. Thanks, Joanne > > -- > Cheers, > > David