Re: Re: [PATCH v2 0/2] btrfs: delay mounted sysfs attributes until mount is ready

[Jiacheng Xu]

Great! Please let me know if the patch is finally merged.

Thanks,
Jiacheng

> -----原始邮件-----
> 发件人: "Qu Wenruo" <wqu@xxxxxxxx>
> 发送时间:2026-08-22 12:57:14 (星期六)
> 收件人: "Jiacheng Xu" <stitch@xxxxxxxxxx>
> 抄送: linux-btrfs@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx
> 主题: Re: [PATCH v2 0/2] btrfs: delay mounted sysfs attributes until mount is ready
> 
> 
> 
> 在 2026/8/22 13:11, Jiacheng Xu 写道:
> > Here is a potential fix following Wenruo's idea.
> > 
> > btrfs_sysfs_add_mounted() currently publishes the writable label and
> > feature attributes before the transaction kthread is created. A concurrent
> > sysfs write can therefore dereference a NULL transaction_kthread in
> > wake_up_process().
> > 
> > This series follows the suggested lifecycle: create only the required
> > subdirectories during early mount, publish the fsid attributes after mount
> > initialization, and remove them before the kthreads are stopped. The
> > feature attributes are included because their store callback has the same
> > transaction_kthread dependency as the label callback.
> > 
> > Patch 1 factors the fsid attribute handling into dedicated helpers. Patch 2
> > moves their publication and removal to the safe mount and unmount stages.
> > On unmount the cleaner is parked before attribute removal so it cannot
> > recreate the feature group through sysfs_update_group(). Both patches are
> > required for stable backports.
> > 
> > The resulting fs/btrfs/sysfs.o and fs/btrfs/disk-io.o were build-tested.
> > 
> > Changes in v2:
> > - Delay creation of both the root and feature attributes until mount setup
> >    is complete.
> 
> You don't need to bother feature attributes for now, there is already a 
> patch addressing it by completely removing the write support for feature 
> attributes:
> 
> https://lore.kernel.org/linux-btrfs/8a598d76555b5944d34bb08fa8dbeea28fc05db9.1787307129.git.wqu@xxxxxxxx/
> 
> Considering it's only extended_iref, removing it should be much simpler.
> Until that is determined, you only need to bother the label one.
> 
> 
> Furthermore, among all the attr files in the fsid directory, there is 
> only label that is writable, it would make more sense to split 
> btrfs_attrs into two parts, one for those read-only members, and one for 
> the only writebale label one.
> 
> Otherwise the series looks much better.
> 
> 
> > - Remove those attributes while their kthread dependencies are still
> >    valid.
> > - Split helper extraction from the lifecycle fix for stable backports.
> > 
> > Jiacheng Xu (2):
> >    btrfs: sysfs: factor out mounted fsid attribute helpers
> >    btrfs: delay mounted fsid attributes until the fs is ready
> > 
> >   fs/btrfs/disk-io.c | 18 ++++++++++++++++-
> >   fs/btrfs/sysfs.c   | 50 ++++++++++++++++++++++++++++++----------------
> >   fs/btrfs/sysfs.h   |  2 ++
> >   3 files changed, 52 insertions(+), 18 deletions(-)
> > 
> > base-commit: 0f23d56f17fdfc7db69d51f64c8b91bbab947aa9