> Aneesh Kumar K.V wrote: > > On Tue, Apr 28, 2009 at 01:00:47PM -0400, Theodore Tso wrote: > >> On Tue, Apr 28, 2009 at 10:05:54PM +0530, Aneesh Kumar K.V wrote: > ... > >>>> The other problem seems to be in the case of a delayed allocation > >>>> write, where we return a buffer_head which is marked new, and this > >>>> causes block_prepare_write() to call unmap_underlying_metadata(dev, 0). > >>> Not just that. On block allocation we are not calling > >>> unmap_underlying_metadata(dev, blocknumber) for delayed allocated > >>> blocks. That would imply file corruption. > >> I don't think I'm following you . If we write into block that was > >> delayed allocated. Are you saying we might get in trouble of the > >> delayed allocation block is mmap'ed in? > > > > We allocate blocks for delayed buffer during writepage. Now we need to > > make sure after getting the blocks we drop the old buffer_head mapping > > that we may have with this particular block attached to the block > > device. That is done by calling unmap_underlying_metadata. Now the > > current code doesn't call unmap_underlying_metadata for delayed > > allocated blocks. That would mean we can see corrupt files if old > > buffer_head mapping gets synced to disk AFTER we write the new > > buffer_head mapping. > > > Talking w/ Aneesh on IRC, I don't see how we can have stray dirty > mappings lying around for this block device unless someone is writing > directly to the mounted block device, which I don't think is ever > considered safe ... > > I'm not quite sure what the call to __unmap_underlying_blocks() in > mpage_da_map_blocks() is for, I guess? For ext3 / ext4 I think we don't need unmap_underlying_blocks() since before we reallocate a block, we make sure that the transaction freeing the block is committed and clear all dirty bits from freed blocks. But for more careless filesystems, if they reallocate metadata block as a data block and don't clear the dirty bit in blockdev mapping, unmap_underlying_blocks() does it for them. Honza -- Jan Kara <jack@xxxxxxx> SuSE CR Labs -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
