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Similar Internal Domain=false; Similar Monitored External Domain=false; Custom External Domain=false; Mimecast External Domain=false; Newly Observed Domain=false; Internal User Name=false; Custom Display Name List=false; Reply-to Address Mismatch=false; Targeted Threat Dictionary=false; Mimecast Threat Dictionary=false; Custom Threat Dictionary=false X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 X-loop: dm-devel@redhat.com Cc: Linux NVDIMM , Mike Snitzer , "Darrick J. Wong" , david , Linux Kernel Mailing List , linux-xfs , Linux MM , device-mapper development , linux-fsdevel , Christoph Hellwig , Alasdair Kergon Subject: Re: [dm-devel] [PATCH RESEND v6 2/9] dax: Introduce holder for dax_device X-BeenThere: dm-devel@redhat.com X-Mailman-Version: 2.1.12 Precedence: junk List-Id: device-mapper development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dm-devel-bounces@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Fri, Jul 30, 2021 at 3:02 AM Shiyang Ruan wrote: > > To easily track filesystem from a pmem device, we introduce a holder for > dax_device structure, and also its operation. This holder is used to > remember who is using this dax_device: > - When it is the backend of a filesystem, the holder will be the > superblock of this filesystem. > - When this pmem device is one of the targets in a mapped device, the > holder will be this mapped device. In this case, the mapped device > has its own dax_device and it will follow the first rule. So that we > can finally track to the filesystem we needed. > > The holder and holder_ops will be set when filesystem is being mounted, > or an target device is being activated. > > Signed-off-by: Shiyang Ruan > --- > drivers/dax/super.c | 46 +++++++++++++++++++++++++++++++++++++++++++++ > include/linux/dax.h | 17 +++++++++++++++++ > 2 files changed, 63 insertions(+) > > diff --git a/drivers/dax/super.c b/drivers/dax/super.c > index 5fa6ae9dbc8b..00c32dfa5665 100644 > --- a/drivers/dax/super.c > +++ b/drivers/dax/super.c > @@ -214,6 +214,8 @@ enum dax_device_flags { > * @cdev: optional character interface for "device dax" > * @host: optional name for lookups where the device path is not available > * @private: dax driver private data > + * @holder_rwsem: prevent unregistration while holder_ops is in progress > + * @holder_data: holder of a dax_device: could be filesystem or mapped device > * @flags: state and boolean properties > */ > struct dax_device { > @@ -222,8 +224,11 @@ struct dax_device { > struct cdev cdev; > const char *host; > void *private; > + struct rw_semaphore holder_rwsem; Given the rarity of notification failures and the infrequency of registration events I think it would be ok for this to be a global lock rather than per-device. In fact there is already a global dax lock, see dax_read_lock(). Let's convert that from srcu to rwsem and add a dax_write_lock(). > + void *holder_data; > unsigned long flags; > const struct dax_operations *ops; > + const struct dax_holder_operations *holder_ops; > }; > > static ssize_t write_cache_show(struct device *dev, > @@ -373,6 +378,25 @@ int dax_zero_page_range(struct dax_device *dax_dev, pgoff_t pgoff, > } > EXPORT_SYMBOL_GPL(dax_zero_page_range); > > +int dax_holder_notify_failure(struct dax_device *dax_dev, loff_t offset, > + size_t size, void *data) > +{ > + int rc; > + > + if (!dax_dev) > + return -ENXIO; There also needs to be a dax_dev->alive check, which is only valid to be checked under dax_read_lock(). Who would ever pass NULL to this function? > + > + if (!dax_dev->holder_data) > + return -EOPNOTSUPP; > + > + down_read(&dax_dev->holder_rwsem); > + rc = dax_dev->holder_ops->notify_failure(dax_dev, offset, > + size, data); > + up_read(&dax_dev->holder_rwsem); > + return rc; > +} > +EXPORT_SYMBOL_GPL(dax_holder_notify_failure); > + > #ifdef CONFIG_ARCH_HAS_PMEM_API > void arch_wb_cache_pmem(void *addr, size_t size); > void dax_flush(struct dax_device *dax_dev, void *addr, size_t size) > @@ -603,6 +627,7 @@ struct dax_device *alloc_dax(void *private, const char *__host, > dax_add_host(dax_dev, host); > dax_dev->ops = ops; > dax_dev->private = private; > + init_rwsem(&dax_dev->holder_rwsem); > if (flags & DAXDEV_F_SYNC) > set_dax_synchronous(dax_dev); > > @@ -624,6 +649,27 @@ void put_dax(struct dax_device *dax_dev) > } > EXPORT_SYMBOL_GPL(put_dax); > > +void dax_set_holder(struct dax_device *dax_dev, void *holder, > + const struct dax_holder_operations *ops) > +{ > + if (!dax_dev) Same questions about NULL dax dev and ->alive checking. > + return; > + down_write(&dax_dev->holder_rwsem); > + dax_dev->holder_data = holder; > + dax_dev->holder_ops = ops; > + up_write(&dax_dev->holder_rwsem); > +} > +EXPORT_SYMBOL_GPL(dax_set_holder); > + > +void *dax_get_holder(struct dax_device *dax_dev) > +{ > + if (!dax_dev) > + return NULL; Where is this API used? This result is not valid unless the caller is holding the read lock. > + > + return dax_dev->holder_data; > +} > +EXPORT_SYMBOL_GPL(dax_get_holder); > + > /** > * dax_get_by_host() - temporary lookup mechanism for filesystem-dax > * @host: alternate name for the device registered by a dax driver > diff --git a/include/linux/dax.h b/include/linux/dax.h > index b52f084aa643..6f4b5c97ceb0 100644 > --- a/include/linux/dax.h > +++ b/include/linux/dax.h > @@ -38,10 +38,17 @@ struct dax_operations { > int (*zero_page_range)(struct dax_device *, pgoff_t, size_t); > }; > > +struct dax_holder_operations { > + int (*notify_failure)(struct dax_device *, loff_t, size_t, void *); > +}; > + > extern struct attribute_group dax_attribute_group; > > #if IS_ENABLED(CONFIG_DAX) > struct dax_device *dax_get_by_host(const char *host); > +void dax_set_holder(struct dax_device *dax_dev, void *holder, > + const struct dax_holder_operations *ops); > +void *dax_get_holder(struct dax_device *dax_dev); > struct dax_device *alloc_dax(void *private, const char *host, > const struct dax_operations *ops, unsigned long flags); > void put_dax(struct dax_device *dax_dev); > @@ -77,6 +84,14 @@ static inline struct dax_device *dax_get_by_host(const char *host) > { > return NULL; > } > +static inline void dax_set_holder(struct dax_device *dax_dev, void *holder, > + const struct dax_holder_operations *ops) > +{ > +} > +static inline void *dax_get_holder(struct dax_device *dax_dev) > +{ > + return NULL; > +} > static inline struct dax_device *alloc_dax(void *private, const char *host, > const struct dax_operations *ops, unsigned long flags) > { > @@ -226,6 +241,8 @@ size_t dax_copy_to_iter(struct dax_device *dax_dev, pgoff_t pgoff, void *addr, > size_t bytes, struct iov_iter *i); > int dax_zero_page_range(struct dax_device *dax_dev, pgoff_t pgoff, > size_t nr_pages); > +int dax_holder_notify_failure(struct dax_device *dax_dev, loff_t offset, > + size_t size, void *data); > void dax_flush(struct dax_device *dax_dev, void *addr, size_t size); > > ssize_t dax_iomap_rw(struct kiocb *iocb, struct iov_iter *iter, > -- > 2.32.0 > > > -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel