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Commit d2c997c0 authored by Dan Williams's avatar Dan Williams
Browse files

fs, dax: use page->mapping to warn if truncate collides with a busy page 



Catch cases where extent unmap operations encounter pages that are
pinned / busy. Typically this is pinned pages that are under active dma.
This warning is a canary for potential data corruption as truncated
blocks could be allocated to a new file while the device is still
performing i/o.

Here is an example of a collision that this implementation catches:

 WARNING: CPU: 2 PID: 1286 at fs/dax.c:343 dax_disassociate_entry+0x55/0x80
 [..]
 Call Trace:
  __dax_invalidate_mapping_entry+0x6c/0xf0
  dax_delete_mapping_entry+0xf/0x20
  truncate_exceptional_pvec_entries.part.12+0x1af/0x200
  truncate_inode_pages_range+0x268/0x970
  ? tlb_gather_mmu+0x10/0x20
  ? up_write+0x1c/0x40
  ? unmap_mapping_range+0x73/0x140
  xfs_free_file_space+0x1b6/0x5b0 [xfs]
  ? xfs_file_fallocate+0x7f/0x320 [xfs]
  ? down_write_nested+0x40/0x70
  ? xfs_ilock+0x21d/0x2f0 [xfs]
  xfs_file_fallocate+0x162/0x320 [xfs]
  ? rcu_read_lock_sched_held+0x3f/0x70
  ? rcu_sync_lockdep_assert+0x2a/0x50
  ? __sb_start_write+0xd0/0x1b0
  ? vfs_fallocate+0x20c/0x270
  vfs_fallocate+0x154/0x270
  SyS_fallocate+0x43/0x80
  entry_SYSCALL_64_fastpath+0x1f/0x96

Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: default avatarJan Kara <jack@suse.cz>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
parent fb094c90

fs/dax.c

+63 −0
Original line number Original line Diff line number Diff line
@@ -298,6 +298,63 @@ static void put_unlocked_mapping_entry(struct address_space *mapping, 
	dax_wake_mapping_entry_waiter(mapping, index, entry, false);

	dax_wake_mapping_entry_waiter(mapping, index, entry, false);

}

}





static unsigned long dax_entry_size(void *entry)

{

	if (dax_is_zero_entry(entry))

		return 0;

	else if (dax_is_empty_entry(entry))

		return 0;

	else if (dax_is_pmd_entry(entry))

		return PMD_SIZE;

	else

		return PAGE_SIZE;

}



static unsigned long dax_radix_end_pfn(void *entry)

{

	return dax_radix_pfn(entry) + dax_entry_size(entry) / PAGE_SIZE;

}



/*

 * Iterate through all mapped pfns represented by an entry, i.e. skip

 * 'empty' and 'zero' entries.

 */

#define for_each_mapped_pfn(entry, pfn) \

	for (pfn = dax_radix_pfn(entry); \

			pfn < dax_radix_end_pfn(entry); pfn++)



static void dax_associate_entry(void *entry, struct address_space *mapping)

{

	unsigned long pfn;



	if (IS_ENABLED(CONFIG_FS_DAX_LIMITED))

		return;



	for_each_mapped_pfn(entry, pfn) {

		struct page *page = pfn_to_page(pfn);



		WARN_ON_ONCE(page->mapping);

		page->mapping = mapping;

	}

}



static void dax_disassociate_entry(void *entry, struct address_space *mapping,

		bool trunc)

{

	unsigned long pfn;



	if (IS_ENABLED(CONFIG_FS_DAX_LIMITED))

		return;



	for_each_mapped_pfn(entry, pfn) {

		struct page *page = pfn_to_page(pfn);



		WARN_ON_ONCE(trunc && page_ref_count(page) > 1);

		WARN_ON_ONCE(page->mapping && page->mapping != mapping);

		page->mapping = NULL;

	}

}



/*

/*

 * Find radix tree entry at given index. If it points to an exceptional entry,

 * 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

 * return it with the radix tree entry locked. If the radix tree doesn't
@@ -404,6 +461,7 @@ static void *grab_mapping_entry(struct address_space *mapping, pgoff_t index, 
		}

		}





		if (pmd_downgrade) {

		if (pmd_downgrade) {

			dax_disassociate_entry(entry, mapping, false);

			radix_tree_delete(&mapping->page_tree, index);

			radix_tree_delete(&mapping->page_tree, index);

			mapping->nrexceptional--;

			mapping->nrexceptional--;

			dax_wake_mapping_entry_waiter(mapping, index, entry,

			dax_wake_mapping_entry_waiter(mapping, index, entry,
@@ -453,6 +511,7 @@ static int __dax_invalidate_mapping_entry(struct address_space *mapping, 
	    (radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_DIRTY) ||

	    (radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_DIRTY) ||

	     radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE)))

	     radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE)))

		goto out;

		goto out;

	dax_disassociate_entry(entry, mapping, trunc);

	radix_tree_delete(page_tree, index);

	radix_tree_delete(page_tree, index);

	mapping->nrexceptional--;

	mapping->nrexceptional--;

	ret = 1;

	ret = 1;
@@ -547,6 +606,10 @@ static void *dax_insert_mapping_entry(struct address_space *mapping, 




	spin_lock_irq(&mapping->tree_lock);

	spin_lock_irq(&mapping->tree_lock);

	new_entry = dax_radix_locked_entry(pfn, flags);

	new_entry = dax_radix_locked_entry(pfn, flags);

	if (dax_entry_size(entry) != dax_entry_size(new_entry)) {

		dax_disassociate_entry(entry, mapping, false);

		dax_associate_entry(new_entry, mapping);

	}





	if (dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) {

	if (dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) {

		/*

		/*