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mm: fix assertion mapping->nrpages == 0 in end_writeback()

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Under heavy memory and filesystem load, users observe the assertion
mapping->nrpages == 0 in end_writeback() trigger.  This can be caused by
page reclaim reclaiming the last page from a mapping in the following
race:

	CPU0				CPU1
  ...
  shrink_page_list()
    __remove_mapping()
      __delete_from_page_cache()
        radix_tree_delete()
					evict_inode()
					  truncate_inode_pages()
					    truncate_inode_pages_range()
					      pagevec_lookup() - finds nothing
					  end_writeback()
					    mapping->nrpages != 0 -> BUG
        page->mapping = NULL
        mapping->nrpages--

Fix the problem by doing a reliable check of mapping->nrpages under
mapping->tree_lock in end_writeback().

Analyzed by Jay <[email protected]>, lost in LKML, and dug out
by Miklos Szeredi <[email protected]>.

Cc: Jay <[email protected]>
Cc: Miklos Szeredi <[email protected]>
Signed-off-by: Jan Kara <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Jan Kara 2011-06-27 16:18:10 -07:00 • committed by Linus Torvalds
commit 08142579b6
3 changed files with 13 additions and 0 deletions
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7
fs/inode.c
View file

@ -423,7 +423,14 @@ EXPORT_SYMBOL(remove_inode_hash);
void end_writeback(struct inode *inode)
{
might_sleep();
/*
* We have to cycle tree_lock here because reclaim can be still in the
* process of removing the last page (in __delete_from_page_cache())
* and we must not free mapping under it.
*/
spin_lock_irq(&inode->i_data.tree_lock);
BUG_ON(inode->i_data.nrpages);
spin_unlock_irq(&inode->i_data.tree_lock);
BUG_ON(!list_empty(&inode->i_data.private_list));
BUG_ON(!(inode->i_state & I_FREEING));
BUG_ON(inode->i_state & I_CLEAR);