On Wed 10-02-16 13:48:54, Ross Zwisler wrote: > During testing of raw block devices + DAX I noticed that the struct > block_device that we were using for DAX operations was incorrect. For the > fault handlers, etc. we can just get the correct bdev via get_block(), > which is passed in as a function pointer, but for the *sync code and for > sector zeroing we don't have access to get_block(). This is also an issue > for XFS real-time devices, whenever we get those working. > > Patch one of this series fixes the DAX sector zeroing code by explicitly > passing in a valid struct block_device. > > Patch two of this series fixes DAX *sync support by moving calls to > dax_writeback_mapping_range() out of filemap_write_and_wait_range() and > into the filesystem/block device ->writepages function so that it can > supply us with a valid block device. This also fixes DAX code to properly > flush caches in response to sync(2). > > Thanks to Jan Kara for his initial draft of patch 2: > https://lkml.org/lkml/2016/2/9/485 > > Here are the changes that I've made to that patch: > > 1) For DAX mappings, only return after calling > dax_writeback_mapping_range() if we encountered an error. In the non-error > case we still need to write back normal pages, else we lose metadata > updates. > > 2) In dax_writeback_mapping_range(), move the new check for > if (!mapping->nrexceptional || wbc->sync_mode != WB_SYNC_ALL) > above the i_blkbits check. In my testing I found cases where > dax_writeback_mapping_range() was called for inodes with i_blkbits != > PAGE_SHIFT - I'm assuming these are internal metadata inodes? They have no > exceptional DAX entries to flush, so we have no work to do, but if we > return error from the i_blkbits check we will fail the overall writeback > operation. Please let me know if it seems wrong for us to be seeing inodes > set to use DAX but with i_blkbits != PAGE_SHIFT and I'll get more info. So I'm wondering - how come S_DAX flag got set for inode where i_blkbis != PAGE_SHIFT? That would seem to be a bug? I specifically ordered the checks like this to catch such issues. > 3) In filemap_write_and_wait() and filemap_write_and_wait_range(), continue > the writeback in the case that DAX is enabled but we only have a nonzero > mapping->nrpages. As with 1) and 2), I believe this is necessary to > properly writeback metadata changes. If this sounds wrong, please let me > know and I'll get more info. And I'm surprised here as well. If there are dax_mapping() inodes that have pagecache pages, then we have issues with radix tree handling as well. So how come dax_mapping() inodes have pages attached? If it is about block device inodes, then I find it buggy, that S_DAX gets set for such inodes when filesystem is mounted on them because in such cases we are IMO asking for data corruption sooner rather than later... Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
