xfs_attr3_root_inactive() walks the attr fork tree to invalidate the associated blocks. xfs_attr3_node_inactive() recursively descends from internal blocks to leaf blocks, caching block address values along the way to revisit parent blocks, locate the next entry and descend down that branch of the tree. The code that attempts to reread the parent block is unsafe because it assumes that the local xfs_da_node_entry pointer remains valid after an xfs_trans_brelse() and re-read of the parent buffer. Under heavy memory pressure, it is possible that the buffer has been reclaimed and reallocated by the time the parent block is reread. This means that 'btree' can point to an invalid memory address, lead to a random/garbage value for child_fsb and cause the subsequent read of the attr fork to go off the rails and return a NULL buffer for an attr fork offset that is most likely not allocated. Note that this problem can be manufactured by setting XFS_ATTR_BTREE_REF to 0 to prevent LRU caching of attr buffers, creating a file with a multi-level attr fork and removing it to trigger inactivation. To address this problem, reinit the node/btree pointers to the parent buffer after it has been re-read. This ensures btree points to a valid record and allows the walk to proceed. Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx> --- I suspect this is the cause of the NULL buf problem down in xfs_attr_inactive(). I can manufacture an instance of that problem as noted above. We have a customer who's hitting that problem and will attempt to validate this fix, but there is no confirmation as of yet. I'm posting this for review in the meantime because this seems like a legit fix regardless of whether they are hitting this or something else. Brian fs/xfs/xfs_attr_inactive.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/fs/xfs/xfs_attr_inactive.c b/fs/xfs/xfs_attr_inactive.c index ebd66b1..e3a950e 100644 --- a/fs/xfs/xfs_attr_inactive.c +++ b/fs/xfs/xfs_attr_inactive.c @@ -302,6 +302,8 @@ xfs_attr3_node_inactive( &bp, XFS_ATTR_FORK); if (error) return error; + node = bp->b_addr; + btree = dp->d_ops->node_tree_p(node); child_fsb = be32_to_cpu(btree[i + 1].before); xfs_trans_brelse(*trans, bp); } -- 2.9.5 -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
