From: Jeff Layton Subject: [PATCH v7 00/22] fs: enhanced writeback error reporting with errseq_t (pile #1) Date: Fri, 16 Jun 2017 15:34:05 -0400 Message-ID: <20170616193427.13955-1-jlayton@redhat.com> Cc: Carlos Maiolino , Eryu Guan , David Howells , Christoph Hellwig , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-block@vger.kernel.org To: Andrew Morton , Al Viro , Jan Kara , tytso@mit.edu, axboe@kernel.dk, mawilcox@microsoft.com, ross.zwisler@linux.intel.com, corbet@lwn.net, Chris Mason , Josef Bacik , David Sterba , "Darrick J . Wong" Return-path: Sender: owner-linux-mm@kvack.org List-Id: linux-ext4.vger.kernel.org v7: === This is the seventh posting of the patchset to revamp the way writeback errors are tracked and reported. The main difference from the v6 posting is the removal of the FS_WB_ERRSEQ flag. That requires a few other incremental patches in the writeback code to ensure that both error tracking models are handled in a suitable way. Also, a bit more cleanup of the metadata writeback codepaths, and some documentation updates. Some of these patches have been posted separately, but I'm re-posting them here to make it clear that they're prerequisites of the later patches in the series. This series is based on top of linux-next from a day or so ago. I'd like to have this picked up by linux-next in the near future so we can get some more extensive testing with it. Should I just plan to maintain a topic branch on top of -next and ask Stephen to pick it up? Background: =========== The basic problem is that we have (for a very long time) tracked and reported writeback errors based on two flags in the address_space: AS_EIO and AS_ENOSPC. Those flags are cleared when they are checked, so only the first caller to check them is able to consume them. That model is quite unreliable, for several related reasons: * only the first fsync caller on the inode will see the error. In a world of containerized setups, that's no longer viable. Applications need to know that their writes are safely stored, and they can currently miss seeing errors that they should be aware of when they're not. * there are a lot of internal callers to filemap_fdatawait* and filemap_write_and_wait* that clear these errors but then never report them to userland in any fashion. * Some internal callers report writeback errors, but can do so at non-sensical times. For instance, we might want to truncate a file, which triggers a pagecache flush. If that writeback fails, we might report that error to the truncate caller, but a subsequent fsync will likely not see it. * Some internal callers try to reset the error flags after clearing them, but that's racy. Another task could check the flags between those two events. Solution: ========= This patchset adds a new datatype called an errseq_t that represents a sequence of errors. It's a u32, with a field for a POSIX-flavor error and a counter, managed with atomics. We can sample that value at a particular point in time, and can later tell whether there have been any errors since that point. That allows us to provide traditional check-and-clear fsync semantics on every open file description in a lightweight fashion. fsync callers no longer need to coordinate between one another in order to ensure that errors at fsync time are handled correctly. Strategy: ========= The aim with this pile is to do the minimum possible to support for reliable reporting of errors on fsync, without substantially changing the internals of the filesystems themselves. Most of the internal calls to filemap_fdatawait are left alone, so all of the internal error checkers are using the same error handling they always have. The only real difference here is that we're better reporting errors at fsync. I think that we probably will want to eventually convert all of those internal callers to use errseq_t based reporting, but that can be done in an incremental fashion in follow-on patchsets. Testing: ======== I've primarily been testing this with some new xfstests that I will post in a separate series. These tests use dm-error fault injection to make the underlying block device start throwing I/O errors, and then test the how the filesystem layer reports errors after that. Jeff Layton (22): fs: remove call_fsync helper function buffer: use mapping_set_error instead of setting the flag fs: check for writeback errors after syncing out buffers in generic_file_fsync buffer: set errors in mapping at the time that the error occurs jbd2: don't clear and reset errors after waiting on writeback mm: clear AS_EIO/AS_ENOSPC when writeback initiation fails mm: don't TestClearPageError in __filemap_fdatawait_range mm: clean up error handling in write_one_page fs: always sync metadata in __generic_file_fsync lib: add errseq_t type and infrastructure for handling it fs: new infrastructure for writeback error handling and reporting mm: tracepoints for writeback error events mm: set both AS_EIO/AS_ENOSPC and errseq_t in mapping_set_error Documentation: flesh out the section in vfs.txt on storing and reporting writeback errors dax: set errors in mapping when writeback fails block: convert to errseq_t based writeback error tracking ext4: use errseq_t based error handling for reporting data writeback errors fs: add f_md_wb_err field to struct file for tracking metadata errors ext4: add more robust reporting of metadata writeback errors ext2: convert to errseq_t based writeback error tracking xfs: minimal conversion to errseq_t writeback error reporting btrfs: minimal conversion to errseq_t writeback error reporting on fsync Documentation/filesystems/vfs.txt | 43 +++++++- drivers/dax/device.c | 1 + fs/block_dev.c | 9 +- fs/btrfs/file.c | 7 +- fs/buffer.c | 20 ++-- fs/dax.c | 4 +- fs/ext2/dir.c | 8 ++ fs/ext2/file.c | 26 ++++- fs/ext4/dir.c | 8 +- fs/ext4/file.c | 5 +- fs/ext4/fsync.c | 28 ++++- fs/file_table.c | 1 + fs/gfs2/lops.c | 2 +- fs/jbd2/commit.c | 15 +-- fs/libfs.c | 12 +-- fs/open.c | 3 + fs/sync.c | 2 +- fs/xfs/xfs_file.c | 15 ++- include/linux/buffer_head.h | 1 + include/linux/errseq.h | 19 ++++ include/linux/fs.h | 67 ++++++++++-- include/linux/pagemap.h | 31 ++++-- include/trace/events/filemap.h | 52 ++++++++++ ipc/shm.c | 2 +- lib/Makefile | 2 +- lib/errseq.c | 208 ++++++++++++++++++++++++++++++++++++++ mm/filemap.c | 113 +++++++++++++++++---- mm/page-writeback.c | 15 ++- 28 files changed, 628 insertions(+), 91 deletions(-) create mode 100644 include/linux/errseq.h create mode 100644 lib/errseq.c -- 2.13.0 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org