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? -Eric -- 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
