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dax: Fix sleep in atomic contex in grab_mapping_entry()

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Commit 642261ac99: "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: 642261ac99
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Jan Kara 2016-12-12 21:34:12 -05:00 committed by Theodore Ts'o
parent 73b92a2a5e
commit 0cb80b4847
1 changed files with 7 additions and 8 deletions
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15
fs/dax.c
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@ -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) {