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authorLinus Torvalds <torvalds@linux-foundation.org>2017-07-07 19:38:17 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-07-07 19:38:17 -0700
commit088737f44bbf6378745f5b57b035e57ee3dc4750 (patch)
tree86a2b1240ea5f7a0ebca837d17a53c07cd07d62a /include/linux/fs.h
parent33198c165b7afd500f7b6b7680ef994296805ef0 (diff)
parent333427a505be1e10d8da13427dc0c33ec1976b99 (diff)
Merge tag 'for-linus-v4.13-2' of git://git.kernel.org/pub/scm/linux/kernel/git/jlayton/linux
Pull Writeback error handling updates from Jeff Layton: "This pile represents the bulk of the writeback error handling fixes that I have for this cycle. Some of the earlier patches in this pile may look trivial but they are prerequisites for later patches in the series. The aim of this set is to improve how we track and report writeback errors to userland. Most applications that care about data integrity will periodically call fsync/fdatasync/msync to ensure that their writes have made it to the backing store. For a very long time, we have tracked writeback errors using two flags in the address_space: AS_EIO and AS_ENOSPC. Those flags are set when a writeback error occurs (via mapping_set_error) and are cleared as a side-effect of filemap_check_errors (as you noted yesterday). This model really sucks for userland. Only the first task to call fsync (or msync or fdatasync) will see the error. Any subsequent task calling fsync on a file will get back 0 (unless another writeback error occurs in the interim). If I have several tasks writing to a file and calling fsync to ensure that their writes got stored, then I need to have them coordinate with one another. That's difficult enough, but in a world of containerized setups that coordination may even not be possible. But wait...it gets worse! The calls to filemap_check_errors can be buried pretty far down in the call stack, and there are internal callers of filemap_write_and_wait and the like that also end up clearing those errors. Many of those callers ignore the error return from that function or return it to userland at nonsensical times (e.g. truncate() or stat()). If I get back -EIO on a truncate, there is no reason to think that it was because some previous writeback failed, and a subsequent fsync() will (incorrectly) return 0. This pile aims to do three things: 1) ensure that when a writeback error occurs that that error will be reported to userland on a subsequent fsync/fdatasync/msync call, regardless of what internal callers are doing 2) report writeback errors on all file descriptions that were open at the time that the error occurred. This is a user-visible change, but I think most applications are written to assume this behavior anyway. Those that aren't are unlikely to be hurt by it. 3) document what filesystems should do when there is a writeback error. Today, there is very little consistency between them, and a lot of cargo-cult copying. We need to make it very clear what filesystems should do in this situation. To achieve this, the set adds a new data type (errseq_t) and then builds new writeback error tracking infrastructure around that. Once all of that is in place, we change the filesystems to use the new infrastructure for reporting wb errors to userland. Note that this is just the initial foray into cleaning up this mess. There is a lot of work remaining here: 1) convert the rest of the filesystems in a similar fashion. Once the initial set is in, then I think most other fs' will be fairly simple to convert. Hopefully most of those can in via individual filesystem trees. 2) convert internal waiters on writeback to use errseq_t for detecting errors instead of relying on the AS_* flags. I have some draft patches for this for ext4, but they are not quite ready for prime time yet. This was a discussion topic this year at LSF/MM too. If you're interested in the gory details, LWN has some good articles about this: https://lwn.net/Articles/718734/ https://lwn.net/Articles/724307/" * tag 'for-linus-v4.13-2' of git://git.kernel.org/pub/scm/linux/kernel/git/jlayton/linux: btrfs: minimal conversion to errseq_t writeback error reporting on fsync xfs: minimal conversion to errseq_t writeback error reporting ext4: use errseq_t based error handling for reporting data writeback errors fs: convert __generic_file_fsync to use errseq_t based reporting block: convert to errseq_t based writeback error tracking dax: set errors in mapping when writeback fails Documentation: flesh out the section in vfs.txt on storing and reporting writeback errors mm: set both AS_EIO/AS_ENOSPC and errseq_t in mapping_set_error fs: new infrastructure for writeback error handling and reporting lib: add errseq_t type and infrastructure for handling it mm: don't TestClearPageError in __filemap_fdatawait_range mm: clear AS_EIO/AS_ENOSPC when writeback initiation fails jbd2: don't clear and reset errors after waiting on writeback buffer: set errors in mapping at the time that the error occurs fs: check for writeback errors after syncing out buffers in generic_file_fsync buffer: use mapping_set_error instead of setting the flag mm: fix mapping_set_error call in me_pagecache_dirty
Diffstat (limited to 'include/linux/fs.h')
-rw-r--r--include/linux/fs.h61
1 files changed, 60 insertions, 1 deletions
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 978fb5966a25..0cfa47125d52 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -32,6 +32,7 @@
#include <linux/workqueue.h>
#include <linux/delayed_call.h>
#include <linux/uuid.h>
+#include <linux/errseq.h>
#include <asm/byteorder.h>
#include <uapi/linux/fs.h>
@@ -401,6 +402,7 @@ struct address_space {
gfp_t gfp_mask; /* implicit gfp mask for allocations */
struct list_head private_list; /* ditto */
void *private_data; /* ditto */
+ errseq_t wb_err;
} __attribute__((aligned(sizeof(long))));
/*
* On most architectures that alignment is already the case; but
@@ -879,6 +881,7 @@ struct file {
struct list_head f_tfile_llink;
#endif /* #ifdef CONFIG_EPOLL */
struct address_space *f_mapping;
+ errseq_t f_wb_err;
} __attribute__((aligned(4))); /* lest something weird decides that 2 is OK */
struct file_handle {
@@ -2536,7 +2539,7 @@ extern int write_inode_now(struct inode *, int);
extern int filemap_fdatawrite(struct address_space *);
extern int filemap_flush(struct address_space *);
extern int filemap_fdatawait(struct address_space *);
-extern void filemap_fdatawait_keep_errors(struct address_space *);
+extern int filemap_fdatawait_keep_errors(struct address_space *mapping);
extern int filemap_fdatawait_range(struct address_space *, loff_t lstart,
loff_t lend);
extern bool filemap_range_has_page(struct address_space *, loff_t lstart,
@@ -2550,6 +2553,62 @@ extern int filemap_fdatawrite_range(struct address_space *mapping,
loff_t start, loff_t end);
extern int filemap_check_errors(struct address_space *mapping);
+extern void __filemap_set_wb_err(struct address_space *mapping, int err);
+extern int __must_check file_check_and_advance_wb_err(struct file *file);
+extern int __must_check file_write_and_wait_range(struct file *file,
+ loff_t start, loff_t end);
+
+/**
+ * filemap_set_wb_err - set a writeback error on an address_space
+ * @mapping: mapping in which to set writeback error
+ * @err: error to be set in mapping
+ *
+ * When writeback fails in some way, we must record that error so that
+ * userspace can be informed when fsync and the like are called. We endeavor
+ * to report errors on any file that was open at the time of the error. Some
+ * internal callers also need to know when writeback errors have occurred.
+ *
+ * When a writeback error occurs, most filesystems will want to call
+ * filemap_set_wb_err to record the error in the mapping so that it will be
+ * automatically reported whenever fsync is called on the file.
+ *
+ * FIXME: mention FS_* flag here?
+ */
+static inline void filemap_set_wb_err(struct address_space *mapping, int err)
+{
+ /* Fastpath for common case of no error */
+ if (unlikely(err))
+ __filemap_set_wb_err(mapping, err);
+}
+
+/**
+ * filemap_check_wb_error - has an error occurred since the mark was sampled?
+ * @mapping: mapping to check for writeback errors
+ * @since: previously-sampled errseq_t
+ *
+ * Grab the errseq_t value from the mapping, and see if it has changed "since"
+ * the given value was sampled.
+ *
+ * If it has then report the latest error set, otherwise return 0.
+ */
+static inline int filemap_check_wb_err(struct address_space *mapping,
+ errseq_t since)
+{
+ return errseq_check(&mapping->wb_err, since);
+}
+
+/**
+ * filemap_sample_wb_err - sample the current errseq_t to test for later errors
+ * @mapping: mapping to be sampled
+ *
+ * Writeback errors are always reported relative to a particular sample point
+ * in the past. This function provides those sample points.
+ */
+static inline errseq_t filemap_sample_wb_err(struct address_space *mapping)
+{
+ return errseq_sample(&mapping->wb_err);
+}
+
extern int vfs_fsync_range(struct file *file, loff_t start, loff_t end,
int datasync);
extern int vfs_fsync(struct file *file, int datasync);