linux-kernel - Re: [PATCH V3 18/21] famfs_fuse: Add holder_operations for dax notify

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Message-ID: <bonriy66ocy6plo66nryagupftobhlnzjr235fukdx7d6vdyku@gzmq25kktdrb>
Date: Fri, 9 Jan 2026 15:00:19 -0600
From: John Groves <John@...ves.net>
To: Jonathan Cameron <jonathan.cameron@...wei.com>
Cc: Miklos Szeredi <miklos@...redi.hu>, 
	Dan Williams <dan.j.williams@...el.com>, Bernd Schubert <bschubert@....com>, 
	Alison Schofield <alison.schofield@...el.com>, John Groves <jgroves@...ron.com>, 
	Jonathan Corbet <corbet@....net>, Vishal Verma <vishal.l.verma@...el.com>, 
	Dave Jiang <dave.jiang@...el.com>, Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>, 
	Alexander Viro <viro@...iv.linux.org.uk>, David Hildenbrand <david@...nel.org>, 
	Christian Brauner <brauner@...nel.org>, "Darrick J . Wong" <djwong@...nel.org>, 
	Randy Dunlap <rdunlap@...radead.org>, Jeff Layton <jlayton@...nel.org>, 
	Amir Goldstein <amir73il@...il.com>, Stefan Hajnoczi <shajnocz@...hat.com>, 
	Joanne Koong <joannelkoong@...il.com>, Josef Bacik <josef@...icpanda.com>, 
	Bagas Sanjaya <bagasdotme@...il.com>, Chen Linxuan <chenlinxuan@...ontech.com>, 
	James Morse <james.morse@....com>, Fuad Tabba <tabba@...gle.com>, 
	Sean Christopherson <seanjc@...gle.com>, Shivank Garg <shivankg@....com>, 
	Ackerley Tng <ackerleytng@...gle.com>, Gregory Price <gourry@...rry.net>, 
	Aravind Ramesh <arramesh@...ron.com>, Ajay Joshi <ajayjoshi@...ron.com>, venkataravis@...ron.com, 
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, nvdimm@...ts.linux.dev, 
	linux-cxl@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH V3 18/21] famfs_fuse: Add holder_operations for dax
 notify_failure()

On 26/01/08 03:17PM, Jonathan Cameron wrote:
> On Wed,  7 Jan 2026 09:33:27 -0600
> John Groves <John@...ves.net> wrote:
> 
> > Memory errors are at least somewhat more likely on disaggregated memory
> > than on-board memory. This commit registers to be notified by fsdev_dax
> > in the event that a memory failure is detected.
> > 
> > When a file access resolves to a daxdev with memory errors, it will fail
> > with an appropriate error.
> > 
> > If a daxdev failed fs_dax_get(), we set dd->dax_err. If a daxdev called
> > our notify_failure(), set dd->error. When any of the above happens, set
> > (file)->error and stop allowing access.
> > 
> > In general, the recovery from memory errors is to unmount the file
> > system and re-initialize the memory, but there may be usable degraded
> > modes of operation - particularly in the future when famfs supports
> > file systems backed by more than one daxdev. In those cases,
> > accessing data that is on a working daxdev can still work.
> > 
> > For now, return errors for any file that has encountered a memory or dax
> > error.
> > 
> > Signed-off-by: John Groves <john@...ves.net>
> > ---
> >  fs/fuse/famfs.c       | 115 +++++++++++++++++++++++++++++++++++++++---
> >  fs/fuse/famfs_kfmap.h |   3 +-
> >  2 files changed, 109 insertions(+), 9 deletions(-)
> > 
> > diff --git a/fs/fuse/famfs.c b/fs/fuse/famfs.c
> > index c02b14789c6e..4eb87c5c628e 100644
> > --- a/fs/fuse/famfs.c
> > +++ b/fs/fuse/famfs.c
> 
> > @@ -254,6 +288,38 @@ famfs_update_daxdev_table(
> >  	return 0;
> >  }
> >  
> > +static void
> > +famfs_set_daxdev_err(
> > +	struct fuse_conn *fc,
> > +	struct dax_device *dax_devp)
> > +{
> > +	int i;
> > +
> > +	/* Gotta search the list by dax_devp;
> > +	 * read lock because we're not adding or removing daxdev entries
> > +	 */
> > +	down_read(&fc->famfs_devlist_sem);
> 
> Use a guard()

Done

> 
> > +	for (i = 0; i < fc->dax_devlist->nslots; i++) {
> > +		if (fc->dax_devlist->devlist[i].valid) {
> > +			struct famfs_daxdev *dd = &fc->dax_devlist->devlist[i];
> > +
> > +			if (dd->devp != dax_devp)
> > +				continue;
> > +
> > +			dd->error = true;
> > +			up_read(&fc->famfs_devlist_sem);
> > +
> > +			pr_err("%s: memory error on daxdev %s (%d)\n",
> > +			       __func__, dd->name, i);
> > +			goto done;
> > +		}
> > +	}
> > +	up_read(&fc->famfs_devlist_sem);
> > +	pr_err("%s: memory err on unrecognized daxdev\n", __func__);
> > +
> > +done:
> 
> If this isn't getting more interesting, just return above.

Right - simplified.

> 
> > +}
> > +
> >  /***************************************************************************/
> >  
> >  void
> > @@ -611,6 +677,26 @@ famfs_file_init_dax(
> >  
> >  static ssize_t famfs_file_bad(struct inode *inode);
> >  
> > +static int famfs_dax_err(struct famfs_daxdev *dd)
> 
> I'd introduce this earlier in the series to reduce need
> to refactor below.

Will mull that over when I further mull the helpers in fuse_i.h that are
hard to rebase...

> 
> > +{
> > +	if (!dd->valid) {
> > +		pr_err("%s: daxdev=%s invalid\n",
> > +		       __func__, dd->name);
> > +		return -EIO;
> > +	}
> > +	if (dd->dax_err) {
> > +		pr_err("%s: daxdev=%s dax_err\n",
> > +		       __func__, dd->name);
> > +		return -EIO;
> > +	}
> > +	if (dd->error) {
> > +		pr_err("%s: daxdev=%s memory error\n",
> > +		       __func__, dd->name);
> > +		return -EHWPOISON;
> > +	}
> > +	return 0;
> > +}
> 
> ...
> 
> > @@ -966,7 +1064,8 @@ famfs_file_bad(struct inode *inode)
> >  		return -EIO;
> >  	}
> >  	if (meta->error) {
> > -		pr_debug("%s: previously detected metadata errors\n", __func__);
> > +		pr_debug("%s: previously detected metadata errors\n",
> > +			 __func__);
> 
> Spurious change.

Derp. Reverted out

Thanks Jonathan