dax: Fix sleep in atomic contex in grab_mapping_entry() (0cb80b48) · Commits · 戴 / test

Commit : "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: Signed-off-by:

Jan Kara <jack@suse.cz> Signed-off-by:

Theodore Ts'o <tytso@mit.edu>

fs/dax.c

+7 −8

Original line number	Diff line number	Diff line
		@@ -333,14 +333,6 @@ restart:
		}

		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 @@ restart:
		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) {

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