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@xxxxxxxxxxx>
---
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
