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 cycling the mapping->tree_lock at the end of
truncate_inode_pages_range() to synchronize with page reclaim.
Analyzed by Jay <[email protected]>, lost in LKML, and dug
out by Miklos Szeredi <[email protected]>.
CC: Jay <[email protected]>
CC: [email protected]
Acked-by: Miklos Szeredi <[email protected]>
Signed-off-by: Jan Kara <[email protected]>
---
mm/truncate.c | 7 +++++++
1 files changed, 7 insertions(+), 0 deletions(-)
Andrew, would you merge this patch please? Thanks.
diff --git a/mm/truncate.c b/mm/truncate.c
index a956675..ec3d292 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -291,6 +291,13 @@ void truncate_inode_pages_range(struct address_space
*mapping,
pagevec_release(&pvec);
mem_cgroup_uncharge_end();
}
+ /*
+ * Cycle the tree_lock to make sure all __delete_from_page_cache()
+ * calls run from page reclaim have finished as well (this handles the
+ * case when page reclaim took the last page from our range).
+ */
+ spin_lock_irq(&mapping->tree_lock);
+ spin_unlock_irq(&mapping->tree_lock);
}
EXPORT_SYMBOL(truncate_inode_pages_range);
--
1.7.1
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