Messages in this thread | | | Subject | Re: [PATCH v7 2/8] dax: Introduce holder for dax_device | From | Shiyang Ruan <> | Date | Wed, 20 Oct 2021 14:58:43 +0800 |
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在 2021/10/15 2:00, Darrick J. Wong 写道: > 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 <ruansy.fnst@fujitsu.com> >> --- >> 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*)
My mistake. I should check @holder_ops instead of @holder_data.
> > 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?
Won't for now. I have tested it with my simple testcases. > > 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?
I didn't think of this case. But I think this uses read lock too. It won't be blocked. Only dax_set_holder() takes write lock.
> >> +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?
Yes.
> >> +} >> +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?
Right.
> >> +}; >> + >> 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...?
It's mistake when I rebase my code to the latest. These lines were deleted but I didn't notice. Will fix it.
-- Thanks, Ruan.
> > --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 >> >> >>
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