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authorDan Williams <dan.j.williams@intel.com>2018-07-13 21:50:16 -0700
committerDave Jiang <dave.jiang@intel.com>2018-07-23 10:38:06 -0700
commitc2a7d2a115525d3501d38e23d24875a79a07e15e (patch)
treedf178de827dbda4bce219d4bfb812581d4883b53 /fs/dax.c
parentae1139ece126b8eb6d0770094fbac43ea928d9d9 (diff)
filesystem-dax: Introduce dax_lock_mapping_entry()
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_mapping_entry() that uses rcu_read_lock() to protect against the inode being freed, and revalidates the page->mapping association under xa_lock(). Cc: Christoph Hellwig <hch@lst.de> Cc: Matthew Wilcox <willy@infradead.org> Cc: Ross Zwisler <ross.zwisler@linux.intel.com> Cc: Jan Kara <jack@suse.cz> Signed-off-by: Dan Williams <dan.j.williams@intel.com> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Diffstat (limited to 'fs/dax.c')
-rw-r--r--fs/dax.c109
1 files changed, 103 insertions, 6 deletions
diff --git a/fs/dax.c b/fs/dax.c
index 4de11ed463ce..57ec272038da 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -226,8 +226,8 @@ static inline void *unlock_slot(struct address_space *mapping, void **slot)
*
* Must be called with the i_pages lock held.
*/
-static void *get_unlocked_mapping_entry(struct address_space *mapping,
- pgoff_t index, void ***slotp)
+static void *__get_unlocked_mapping_entry(struct address_space *mapping,
+ pgoff_t index, void ***slotp, bool (*wait_fn)(void))
{
void *entry, **slot;
struct wait_exceptional_entry_queue ewait;
@@ -237,6 +237,8 @@ static void *get_unlocked_mapping_entry(struct address_space *mapping,
ewait.wait.func = wake_exceptional_entry_func;
for (;;) {
+ bool revalidate;
+
entry = __radix_tree_lookup(&mapping->i_pages, index, NULL,
&slot);
if (!entry ||
@@ -251,14 +253,31 @@ static void *get_unlocked_mapping_entry(struct address_space *mapping,
prepare_to_wait_exclusive(wq, &ewait.wait,
TASK_UNINTERRUPTIBLE);
xa_unlock_irq(&mapping->i_pages);
- schedule();
+ revalidate = wait_fn();
finish_wait(wq, &ewait.wait);
xa_lock_irq(&mapping->i_pages);
+ if (revalidate)
+ return ERR_PTR(-EAGAIN);
}
}
-static void dax_unlock_mapping_entry(struct address_space *mapping,
- pgoff_t index)
+static bool entry_wait(void)
+{
+ schedule();
+ /*
+ * Never return an ERR_PTR() from
+ * __get_unlocked_mapping_entry(), just keep looping.
+ */
+ return false;
+}
+
+static void *get_unlocked_mapping_entry(struct address_space *mapping,
+ pgoff_t index, void ***slotp)
+{
+ return __get_unlocked_mapping_entry(mapping, index, slotp, entry_wait);
+}
+
+static void unlock_mapping_entry(struct address_space *mapping, pgoff_t index)
{
void *entry, **slot;
@@ -277,7 +296,7 @@ static void dax_unlock_mapping_entry(struct address_space *mapping,
static void put_locked_mapping_entry(struct address_space *mapping,
pgoff_t index)
{
- dax_unlock_mapping_entry(mapping, index);
+ unlock_mapping_entry(mapping, index);
}
/*
@@ -374,6 +393,84 @@ static struct page *dax_busy_page(void *entry)
return NULL;
}
+static bool entry_wait_revalidate(void)
+{
+ rcu_read_unlock();
+ schedule();
+ rcu_read_lock();
+
+ /*
+ * Tell __get_unlocked_mapping_entry() to take a break, we need
+ * to revalidate page->mapping after dropping locks
+ */
+ return true;
+}
+
+bool dax_lock_mapping_entry(struct page *page)
+{
+ pgoff_t index;
+ struct inode *inode;
+ bool did_lock = false;
+ void *entry = NULL, **slot;
+ struct address_space *mapping;
+
+ rcu_read_lock();
+ for (;;) {
+ mapping = READ_ONCE(page->mapping);
+
+ if (!dax_mapping(mapping))
+ break;
+
+ /*
+ * In the device-dax case there's no need to lock, a
+ * struct dev_pagemap pin is sufficient to keep the
+ * inode alive, and we assume we have dev_pagemap pin
+ * otherwise we would not have a valid pfn_to_page()
+ * translation.
+ */
+ inode = mapping->host;
+ if (S_ISCHR(inode->i_mode)) {
+ did_lock = true;
+ break;
+ }
+
+ xa_lock_irq(&mapping->i_pages);
+ if (mapping != page->mapping) {
+ xa_unlock_irq(&mapping->i_pages);
+ continue;
+ }
+ index = page->index;
+
+ entry = __get_unlocked_mapping_entry(mapping, index, &slot,
+ entry_wait_revalidate);
+ if (!entry) {
+ xa_unlock_irq(&mapping->i_pages);
+ break;
+ } else if (IS_ERR(entry)) {
+ WARN_ON_ONCE(PTR_ERR(entry) != -EAGAIN);
+ continue;
+ }
+ lock_slot(mapping, slot);
+ did_lock = true;
+ xa_unlock_irq(&mapping->i_pages);
+ break;
+ }
+ rcu_read_unlock();
+
+ return did_lock;
+}
+
+void dax_unlock_mapping_entry(struct page *page)
+{
+ struct address_space *mapping = page->mapping;
+ struct inode *inode = mapping->host;
+
+ if (S_ISCHR(inode->i_mode))
+ return;
+
+ 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