dax: Fix sleep in atomic contex in grab_mapping_entry()
Commit 642261ac995e: "dax: add struct iomap based DAX PMD support" has
introduced unmapping of page tables if huge page needs to be split in
grab_mapping_entry(). However the unmapping happens after
radix_tree_preload() call which disables preemption and thus
unmap_mapping_range() tries to acquire i_mmap_lock in atomic context
which is a bug. Fix the problem by moving unmapping before
radix_tree_preload() call.
Fixes: 642261ac995e01d7837db1f4b90181496f7e6835
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
diff --git a/fs/dax.c b/fs/dax.c
index ad131cd..5bfd27b 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -333,14 +333,6 @@ static void *grab_mapping_entry(struct address_space *mapping, pgoff_t index,
}
spin_unlock_irq(&mapping->tree_lock);
- err = radix_tree_preload(
- mapping_gfp_mask(mapping) & ~__GFP_HIGHMEM);
- if (err) {
- if (pmd_downgrade)
- put_locked_mapping_entry(mapping, index, entry);
- return ERR_PTR(err);
- }
-
/*
* Besides huge zero pages the only other thing that gets
* downgraded are empty entries which don't need to be
@@ -350,6 +342,13 @@ static void *grab_mapping_entry(struct address_space *mapping, pgoff_t index,
unmap_mapping_range(mapping,
(index << PAGE_SHIFT) & PMD_MASK, PMD_SIZE, 0);
+ err = radix_tree_preload(
+ mapping_gfp_mask(mapping) & ~__GFP_HIGHMEM);
+ if (err) {
+ if (pmd_downgrade)
+ put_locked_mapping_entry(mapping, index, entry);
+ return ERR_PTR(err);
+ }
spin_lock_irq(&mapping->tree_lock);
if (pmd_downgrade) {