From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 91DEF2C80 for ; Thu, 14 Oct 2021 18:00:26 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id 218CB61056; Thu, 14 Oct 2021 18:00:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1634234426; bh=kNjkeDBzuQfKoxHXcqV0S2llnADIp119vN6i/9sLhI0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=G+2O+xStpmBdi2GvmMWeubjNCIO1twn71R2X9fWluUEAyGo3Si35GkyuwT73m2Cj2 djRXu/apHaUwV+JT5JfphXPS0aquut7uuFllJdLigvBAOVyJdZohTpOK7tIT44xFgi HnWZYT1YZHjyH1cVLcEs0yQw31IexSnUHC+tvGy9GusWytkK9TiJMaSGYnH2em7IsD 7mybQ9s2WZ+TOb/8eX6OubU8D1O+0hnsmjrg3E4fP8UpIInWtMMnoh1iZIxAnSUs8/ 2xLgsR/+OBsMaJCsyvCOkYeihH9cghkssYwvRv0n67UwWs/GSck8bIDV5m2A1ukzXl kReRVmUiaL9VQ== Date: Thu, 14 Oct 2021 11:00:25 -0700 From: "Darrick J. Wong" To: Shiyang Ruan Cc: linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org, nvdimm@lists.linux.dev, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, dan.j.williams@intel.com, david@fromorbit.com, hch@infradead.org, jane.chu@oracle.com Subject: Re: [PATCH v7 2/8] dax: Introduce holder for dax_device Message-ID: <20211014180025.GC24333@magnolia> References: <20210924130959.2695749-1-ruansy.fnst@fujitsu.com> <20210924130959.2695749-3-ruansy.fnst@fujitsu.com> Precedence: bulk X-Mailing-List: nvdimm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210924130959.2695749-3-ruansy.fnst@fujitsu.com> On Fri, Sep 24, 2021 at 09:09:53PM +0800, 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 | 59 +++++++++++++++++++++++++++++++++++++++++++++ > include/linux/dax.h | 29 ++++++++++++++++++++++ > 2 files changed, 88 insertions(+) > > diff --git a/drivers/dax/super.c b/drivers/dax/super.c > index 48ce86501d93..7d4a11dcba90 100644 > --- a/drivers/dax/super.c > +++ b/drivers/dax/super.c > @@ -23,7 +23,10 @@ > * @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_data: holder of a dax_device: could be filesystem or mapped device > * @flags: state and boolean properties > + * @ops: operations for dax_device > + * @holder_ops: operations for the inner holder > */ > struct dax_device { > struct hlist_node list; > @@ -31,8 +34,10 @@ struct dax_device { > struct cdev cdev; > const char *host; > void *private; > + void *holder_data; > unsigned long flags; > const struct dax_operations *ops; > + const struct dax_holder_operations *holder_ops; > }; > > static dev_t dax_devt; > @@ -374,6 +379,29 @@ 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, int flags) > +{ > + int rc; > + > + dax_read_lock(); > + if (!dax_alive(dax_dev)) { > + rc = -ENXIO; > + goto out; > + } > + > + if (!dax_dev->holder_data) { > + rc = -EOPNOTSUPP; > + goto out; > + } > + > + rc = dax_dev->holder_ops->notify_failure(dax_dev, offset, size, flags); Shouldn't this check if dax_dev->holder_ops != NULL before dereferencing it for the function call? Imagine an implementation that wants to attach a ->notify_failure function to a dax_device, maintains its own lookup table, and decides that it doesn't need to set holder_data. (Or, imagine someone who writes a garbage into holder_data and *boom*) How does the locking work here? If there's a media failure, we'll take dax_rwsem and call ->notify_failure. If the ->notify_failure function wants to access the pmem to handle the error by calling back into the dax code, will that cause nested locking on dax_rwsem? Jumping ahead a bit, I think the rmap btree accesses that the xfs implementation performs can cause xfs_buf(fer) cache IO, which would trigger that if the buffers aren't already in memory, if I'm reading this correctly? > +out: > + dax_read_unlock(); > + 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) > @@ -618,6 +646,37 @@ 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) > +{ > + dax_write_lock(); > + if (!dax_alive(dax_dev)) { > + dax_write_unlock(); > + return; > + } > + > + dax_dev->holder_data = holder; > + dax_dev->holder_ops = ops; > + dax_write_unlock(); I guess this means that the holder has to detach itself before anyone calls kill_dax, or else a dead dax device ends up with a dangling reference to the holder? > +} > +EXPORT_SYMBOL_GPL(dax_set_holder); > + > +void *dax_get_holder(struct dax_device *dax_dev) > +{ > + void *holder; > + > + dax_read_lock(); > + if (!dax_alive(dax_dev)) { > + dax_read_unlock(); > + return NULL; > + } > + > + holder = dax_dev->holder_data; > + dax_read_unlock(); > + return holder; > +} > +EXPORT_SYMBOL_GPL(dax_get_holder); > + > /** > * inode_dax: convert a public inode into its dax_dev > * @inode: An inode with i_cdev pointing to a dax_dev > diff --git a/include/linux/dax.h b/include/linux/dax.h > index 097b3304f9b9..d273d59723cd 100644 > --- a/include/linux/dax.h > +++ b/include/linux/dax.h > @@ -38,9 +38,24 @@ struct dax_operations { > int (*zero_page_range)(struct dax_device *, pgoff_t, size_t); > }; > > +struct dax_holder_operations { > + /* > + * notify_failure - notify memory failure into inner holder device > + * @dax_dev: the dax device which contains the holder > + * @offset: offset on this dax device where memory failure occurs > + * @size: length of this memory failure event > + * @flags: action flags for memory failure handler > + */ > + int (*notify_failure)(struct dax_device *dax_dev, loff_t offset, > + size_t size, int flags); Shouldn't size be u64 or something? Let's say that 8GB of your pmem go bad, wouldn't you want a single call? Though I guess the current implementation only goes a single page at a time, doesn't it? > +}; > + > extern struct attribute_group dax_attribute_group; > > #if IS_ENABLED(CONFIG_DAX) > +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); > @@ -70,6 +85,18 @@ static inline bool daxdev_mapping_supported(struct vm_area_struct *vma, > return dax_synchronous(dax_dev); > } > #else > +static inline struct dax_device *dax_get_by_host(const char *host) Not sure why this is being added here? AFAICT none of the patches call this function...? --D > +{ > + 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) > { > @@ -198,6 +225,8 @@ 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, int flags); > 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, > -- > 2.33.0 > > >