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From: "ruansy.fnst@fujitsu.com" <ruansy.fnst@fujitsu.com>
To: Christoph Hellwig <hch@lst.de>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-xfs@vger.kernel.org" <linux-xfs@vger.kernel.org>,
	"nvdimm@lists.linux.dev" <nvdimm@lists.linux.dev>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	"dm-devel@redhat.com" <dm-devel@redhat.com>,
	"darrick.wong@oracle.com" <darrick.wong@oracle.com>,
	"dan.j.williams@intel.com" <dan.j.williams@intel.com>,
	"david@fromorbit.com" <david@fromorbit.com>,
	"agk@redhat.com" <agk@redhat.com>,
	"snitzer@redhat.com" <snitzer@redhat.com>,
	"rgoldwyn@suse.de" <rgoldwyn@suse.de>
Subject: RE: [PATCH v5 2/9] dax: Introduce holder for dax_device
Date: Tue, 20 Jul 2021 10:37:26 +0000	[thread overview]
Message-ID: <OSBPR01MB29200552738339C054E70A1FF4E29@OSBPR01MB2920.jpnprd01.prod.outlook.com> (raw)
In-Reply-To: <20210719151744.GA22718@lst.de>

> -----Original Message-----
> Subject: Re: [PATCH v5 2/9] dax: Introduce holder for dax_device
> 
> On Mon, Jun 28, 2021 at 08:02:11AM +0800, Shiyang Ruan wrote:
> > +int dax_holder_notify_failure(struct dax_device *dax_dev, loff_t offset,
> > +			      size_t size, void *data)
> > +{
> > +	int rc = -ENXIO;
> > +	if (!dax_dev)
> > +		return rc;
> > +
> > +	if (dax_dev->holder_data) {
> > +		rc = dax_dev->holder_ops->notify_failure(dax_dev, offset,
> > +							 size, data);
> > +		if (rc == -ENODEV)
> > +			rc = -ENXIO;
> > +	} else
> > +		rc = -EOPNOTSUPP;
> 
> The style looks a little odd.  Why not:
> 
> 	if (!dax_dev)
> 		return -ENXIO
> 	if (!dax_dev->holder_data)
> 		return -EOPNOTSUPP;
> 	return dax_dev->holder_ops->notify_failure(dax_dev, offset, size, data);
> 
> and let everyone deal with the same errno codes?
OK.

> 
> Also why do we even need the dax_dev NULL check?

Because this dax_dev is obtain by fs_dax_get_by_bdev() in XFS and dax_get_by_host() in MD.  According to their definition, NULL may be returned.  So I check the dax_dev here.

> 
> > +void dax_set_holder(struct dax_device *dax_dev, void *holder,
> > +		const struct dax_holder_operations *ops) {
> > +	if (!dax_dev)
> > +		return;
> 
> I don't think we really need that check here.
> 
> > +void *dax_get_holder(struct dax_device *dax_dev) {
> > +	void *holder_data;
> > +
> > +	if (!dax_dev)
> > +		return NULL;
> 
> Same here.
> 
> > +
> > +	down_read(&dax_dev->holder_rwsem);
> > +	holder_data = dax_dev->holder_data;
> > +	up_read(&dax_dev->holder_rwsem);
> > +
> > +	return holder_data;
> 
> That lock won't protect anything.  I think we simply must have synchronization
> to prevent unregistration while the ->notify_failure call is in progress.

Yes, I misunderstood the purpose of the lock. I'll fix this.


--
Thanks,
Ruan.

  reply	other threads:[~2021-07-20 10:38 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-28  0:02 [PATCH v5 0/9] fsdax: introduce fs query to support reflink Shiyang Ruan
2021-06-28  0:02 ` [PATCH v5 1/9] pagemap: Introduce ->memory_failure() Shiyang Ruan
2021-06-28  0:02 ` [PATCH v5 2/9] dax: Introduce holder for dax_device Shiyang Ruan
2021-07-19 15:17   ` Christoph Hellwig
2021-07-20 10:37     ` ruansy.fnst [this message]
2021-06-28  0:02 ` [PATCH v5 3/9] mm: factor helpers for memory_failure_dev_pagemap Shiyang Ruan
2021-06-28  0:02 ` [PATCH v5 4/9] pmem,mm: Implement ->memory_failure in pmem driver Shiyang Ruan
2021-06-28  0:02 ` [PATCH v5 5/9] mm: Introduce mf_dax_kill_procs() for fsdax case Shiyang Ruan
2021-06-28  3:23   ` kernel test robot
2021-06-28 11:49   ` Matthew Wilcox
2021-06-29  7:49     ` ruansy.fnst
2021-06-29 11:46       ` Matthew Wilcox
2021-07-16  6:32         ` ruansy.fnst
2021-06-28  0:02 ` [PATCH v5 6/9] xfs: Implement ->corrupted_range() for XFS Shiyang Ruan
2021-06-28  2:02   ` kernel test robot
2021-06-28  3:05   ` kernel test robot
2021-06-28  0:02 ` [PATCH v5 7/9] dm: Introduce ->rmap() to find bdev offset Shiyang Ruan
2021-06-28  0:02 ` [PATCH v5 8/9] md: Implement dax_holder_operations Shiyang Ruan
2021-06-28  0:02 ` [PATCH v5 9/9] fs/dax: Remove useless functions Shiyang Ruan
2021-07-19 15:18   ` Christoph Hellwig

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