In preparation for implementing support for memory poison (media error)
handling via dax mappings, implement a lock_page() equivalent. Poison
error handling requires rmap and needs guarantees that the page->mapping
association is maintained / valid (inode not freed) for the duration of
the lookup.
In the device-dax case it is sufficient to simply hold a dev_pagemap
reference. In the filesystem-dax case we need to use the entry lock.
Export the entry lock via dax_lock_page() that uses rcu_read_lock() to
protect against the inode being freed, and revalidates the page->mapping
association under xa_lock().
Signed-off-by: Dan Williams <dan.j.willi...@intel.com>
---
fs/dax.c | 76 +++++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/dax.h | 15 ++++++++++
2 files changed, 91 insertions(+)
diff --git a/fs/dax.c b/fs/dax.c
index cccf6cad1a7a..b7e71b108fcf 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -361,6 +361,82 @@ static void dax_disassociate_entry(void *entry, struct
address_space *mapping,
}
}
+struct page *dax_lock_page(unsigned long pfn)
+{
+ pgoff_t index;
+ struct inode *inode;
+ wait_queue_head_t *wq;
+ void *entry = NULL, **slot;
+ struct address_space *mapping;
+ struct wait_exceptional_entry_queue ewait;
+ struct page *ret = NULL, *page = pfn_to_page(pfn);
+
+ rcu_read_lock();
+ for (;;) {
+ mapping = READ_ONCE(page->mapping);
+
+ if (!mapping || !IS_DAX(mapping->host))
+ break;
+
+ /*
+ * In the device-dax case there's no need to lock, a
+ * struct dev_pagemap pin is sufficient to keep the
+ * inode alive.
+ */
+ inode = mapping->host;
+ if (S_ISCHR(inode->i_mode)) {
+ ret = page;
+ break;
+ }
+
+ xa_lock_irq(&mapping->i_pages);
+ if (mapping != page->mapping) {
+ xa_unlock_irq(&mapping->i_pages);
+ continue;
+ }
+ index = page->index;
+
+ init_wait(&ewait.wait);
+ ewait.wait.func = wake_exceptional_entry_func;
+
+ entry = __radix_tree_lookup(&mapping->i_pages, index, NULL,
+ &slot);
+ if (!entry ||
+ WARN_ON_ONCE(!radix_tree_exceptional_entry(entry))) {
+ xa_unlock_irq(&mapping->i_pages);
+ break;
+ } else if (!slot_locked(mapping, slot)) {
+ lock_slot(mapping, slot);
+ ret = page;
+ xa_unlock_irq(&mapping->i_pages);
+ break;
+ }
+
+ wq = dax_entry_waitqueue(mapping, index, entry, &ewait.key);
+ prepare_to_wait_exclusive(wq, &ewait.wait,
+ TASK_UNINTERRUPTIBLE);
+ xa_unlock_irq(&mapping->i_pages);
+ rcu_read_unlock();
+ schedule();
+ finish_wait(wq, &ewait.wait);
+ rcu_read_lock();
+ }
+ rcu_read_unlock();
+
+ return page;
+}
+
+void dax_unlock_page(struct page *page)
+{
+ struct address_space *mapping = page->mapping;
+ struct inode *inode = mapping->host;
+
+ if (S_ISCHR(inode->i_mode))
+ return;
+
+ dax_unlock_mapping_entry(mapping, page->index);
+}
+
/*
* Find radix tree entry at given index. If it points to an exceptional entry,
* return it with the radix tree entry locked. If the radix tree doesn't
diff --git a/include/linux/dax.h b/include/linux/dax.h
index f9eb22ad341e..641cab7e1fa7 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -83,6 +83,8 @@ static inline void fs_put_dax(struct dax_device *dax_dev)
struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev);
int dax_writeback_mapping_range(struct address_space *mapping,
struct block_device *bdev, struct writeback_control *wbc);
+struct page *dax_lock_page(unsigned long pfn);
+void dax_unlock_page(struct page *page);
#else
static inline int bdev_dax_supported(struct super_block *sb, int blocksize)
{
@@ -108,6 +110,19 @@ static inline int dax_writeback_mapping_range(struct
address_space *mapping,
{
return -EOPNOTSUPP;
}
+
+static inline struct page *dax_lock_page(unsigned long pfn)
+{
+ struct page *page = pfn_to_page(pfn);
+
+ if (IS_DAX(page->mapping->host))
+ return page;
+ return NULL;
+}
+
+static inline void dax_unlock_page(struct page *page)
+{
+}
#endif
int dax_read_lock(void);
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