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[198.145.29.99]) by mx.google.com with ESMTPS id c198si3499580oib.24.2017.06.29.06.19.58 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 29 Jun 2017 06:19:58 -0700 (PDT) From: jlayton@kernel.org Subject: [PATCH v8 00/18] fs: enhanced writeback error reporting with errseq_t (pile #1) Date: Thu, 29 Jun 2017 09:19:36 -0400 Message-Id: <20170629131954.28733-1-jlayton@kernel.org> Sender: owner-linux-mm@kvack.org List-ID: 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" Cc: Carlos Maiolino , Eryu Guan , David Howells , Christoph Hellwig , Liu Bo , 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 From: Jeff Layton v8: === - rename filemap_report_wb_err to file_check_and_advance_wb_err (per Darrick's suggestion) - add a file_write_and_wait helper function (per HCH's suggestion) - change __generic_file_fsync to use errseq_t reporting - focus on data writeback for now, leave metadata for a follow-on set - drop patch to always do metadata writeback in __generic_file_fsync This is the eighth posting of the patchset to revamp the way writeback errors are tracked and reported. Some of these patches are not new, but I want to make it clear what I'd like to get merged into v4.13. The main changes since the last set are a name change for the "report" function to better indicate that it has side-effects. Also, I've added a file_write_and_wait function to act as an analogue of the old filemap_write_and_wait, but that uses errseq_t reporting. With that change, it became pretty easy to convert __generic_file_fsync, so I've gone ahead and done that. vfat now passes the simple testcase as well. Finally, I've dropped off a few patches here that were intended to make it possible to report metadata writeback errors on all open fds as well. That part is turning out to be trickier than expected, so I've decided to just focus on data writeback here. We can pick up that piece in a later patcheset. If no one has major objections, I'll plan to send Linus a PR with this pile once the merge window opens (unless someone else wants to pick it up...Al?). 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 (18): 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 lib: add errseq_t type and infrastructure for handling it fs: new infrastructure for writeback error handling and reporting 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 fs: convert __generic_file_fsync to use errseq_t based reporting ext4: use errseq_t based error handling for reporting data writeback errors 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 +++++++- MAINTAINERS | 6 ++ drivers/dax/device.c | 1 + fs/block_dev.c | 3 +- fs/btrfs/file.c | 7 +- fs/buffer.c | 20 ++-- fs/dax.c | 4 +- fs/ext2/file.c | 5 +- fs/ext4/fsync.c | 13 ++- fs/file_table.c | 1 + fs/gfs2/lops.c | 2 +- fs/jbd2/commit.c | 16 +-- fs/libfs.c | 6 +- fs/open.c | 3 + fs/sync.c | 2 +- fs/xfs/xfs_file.c | 2 +- include/linux/buffer_head.h | 1 + include/linux/errseq.h | 19 ++++ include/linux/fs.h | 68 +++++++++++-- include/linux/pagemap.h | 31 ++++-- include/trace/events/filemap.h | 57 +++++++++++ ipc/shm.c | 2 +- lib/Makefile | 2 +- lib/errseq.c | 208 ++++++++++++++++++++++++++++++++++++++ mm/filemap.c | 128 +++++++++++++++++++---- mm/page-writeback.c | 13 ++- 26 files changed, 584 insertions(+), 79 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. 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