On Mon, Nov 06, 2017 at 11:26:26PM +0100, Luis R. Rodriguez wrote: > On Wed, Oct 11, 2017 at 02:11:44PM -0300, Marco Benatto wrote: > > Hello all > > > > On Fri, Oct 6, 2017 at 5:47 PM, Darrick J. Wong <darrick.wong@xxxxxxxxxx> wrote: > > > > > > On Fri, Oct 06, 2017 at 04:07:40PM -0400, Brian Foster wrote: > > > > 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> > > > > > > Looks ok, > > > Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> > > > > > > /me wonders if this is a good enough reason to introduce a new errortag > > > that turns xfs_buf_set_ref into a no-op and fills bp->b_addr with > > > garbage prior to releasing the memory to weed out any other dangling > > > pointers? > > > > > > > --- > > > > > > > > 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. > > > > > > Let me know what they report back. > > > > Just to let you know, we've got some news regarding this testing and the > > patch seems effective to fix the issue they were facing before at > > xfs_attr_inactive() case. > > Is there an actual oops trace that is reported somewhere? I didn't see it > provided. > I believe it is this thread: https://www.spinics.net/lists/linux-xfs/msg06695.html Brian > Luis > -- > 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 -- 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
