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authorLinus Torvalds <torvalds@linux-foundation.org>2017-07-08 05:38:17 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2017-07-08 05:38:17 +0300
commit088737f44bbf6378745f5b57b035e57ee3dc4750 (patch)
tree86a2b1240ea5f7a0ebca837d17a53c07cd07d62a /mm/filemap.c
parent33198c165b7afd500f7b6b7680ef994296805ef0 (diff)
parent333427a505be1e10d8da13427dc0c33ec1976b99 (diff)
downloadlinux-088737f44bbf6378745f5b57b035e57ee3dc4750.tar.xz
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 'mm/filemap.c')
-rw-r--r--mm/filemap.c126
1 files changed, 109 insertions, 17 deletions
diff --git a/mm/filemap.c b/mm/filemap.c
index 2e906ef52143..3247b4208034 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -309,6 +309,16 @@ int filemap_check_errors(struct address_space *mapping)
}
EXPORT_SYMBOL(filemap_check_errors);
+static int filemap_check_and_keep_errors(struct address_space *mapping)
+{
+ /* Check for outstanding write errors */
+ if (test_bit(AS_EIO, &mapping->flags))
+ return -EIO;
+ if (test_bit(AS_ENOSPC, &mapping->flags))
+ return -ENOSPC;
+ return 0;
+}
+
/**
* __filemap_fdatawrite_range - start writeback on mapping dirty pages in range
* @mapping: address space structure to write
@@ -408,17 +418,16 @@ bool filemap_range_has_page(struct address_space *mapping,
}
EXPORT_SYMBOL(filemap_range_has_page);
-static int __filemap_fdatawait_range(struct address_space *mapping,
+static void __filemap_fdatawait_range(struct address_space *mapping,
loff_t start_byte, loff_t end_byte)
{
pgoff_t index = start_byte >> PAGE_SHIFT;
pgoff_t end = end_byte >> PAGE_SHIFT;
struct pagevec pvec;
int nr_pages;
- int ret = 0;
if (end_byte < start_byte)
- goto out;
+ return;
pagevec_init(&pvec, 0);
while ((index <= end) &&
@@ -435,14 +444,11 @@ static int __filemap_fdatawait_range(struct address_space *mapping,
continue;
wait_on_page_writeback(page);
- if (TestClearPageError(page))
- ret = -EIO;
+ ClearPageError(page);
}
pagevec_release(&pvec);
cond_resched();
}
-out:
- return ret;
}
/**
@@ -462,14 +468,8 @@ out:
int filemap_fdatawait_range(struct address_space *mapping, loff_t start_byte,
loff_t end_byte)
{
- int ret, ret2;
-
- ret = __filemap_fdatawait_range(mapping, start_byte, end_byte);
- ret2 = filemap_check_errors(mapping);
- if (!ret)
- ret = ret2;
-
- return ret;
+ __filemap_fdatawait_range(mapping, start_byte, end_byte);
+ return filemap_check_errors(mapping);
}
EXPORT_SYMBOL(filemap_fdatawait_range);
@@ -485,15 +485,17 @@ EXPORT_SYMBOL(filemap_fdatawait_range);
* call sites are system-wide / filesystem-wide data flushers: e.g. sync(2),
* fsfreeze(8)
*/
-void filemap_fdatawait_keep_errors(struct address_space *mapping)
+int filemap_fdatawait_keep_errors(struct address_space *mapping)
{
loff_t i_size = i_size_read(mapping->host);
if (i_size == 0)
- return;
+ return 0;
__filemap_fdatawait_range(mapping, 0, i_size - 1);
+ return filemap_check_and_keep_errors(mapping);
}
+EXPORT_SYMBOL(filemap_fdatawait_keep_errors);
/**
* filemap_fdatawait - wait for all under-writeback pages to complete
@@ -535,6 +537,9 @@ int filemap_write_and_wait(struct address_space *mapping)
int err2 = filemap_fdatawait(mapping);
if (!err)
err = err2;
+ } else {
+ /* Clear any previously stored errors */
+ filemap_check_errors(mapping);
}
} else {
err = filemap_check_errors(mapping);
@@ -569,6 +574,9 @@ int filemap_write_and_wait_range(struct address_space *mapping,
lstart, lend);
if (!err)
err = err2;
+ } else {
+ /* Clear any previously stored errors */
+ filemap_check_errors(mapping);
}
} else {
err = filemap_check_errors(mapping);
@@ -577,6 +585,90 @@ int filemap_write_and_wait_range(struct address_space *mapping,
}
EXPORT_SYMBOL(filemap_write_and_wait_range);
+void __filemap_set_wb_err(struct address_space *mapping, int err)
+{
+ errseq_t eseq = __errseq_set(&mapping->wb_err, err);
+
+ trace_filemap_set_wb_err(mapping, eseq);
+}
+EXPORT_SYMBOL(__filemap_set_wb_err);
+
+/**
+ * file_check_and_advance_wb_err - report wb error (if any) that was previously
+ * and advance wb_err to current one
+ * @file: struct file on which the error is being reported
+ *
+ * When userland calls fsync (or something like nfsd does the equivalent), we
+ * want to report any writeback errors that occurred since the last fsync (or
+ * since the file was opened if there haven't been any).
+ *
+ * Grab the wb_err from the mapping. If it matches what we have in the file,
+ * then just quickly return 0. The file is all caught up.
+ *
+ * If it doesn't match, then take the mapping value, set the "seen" flag in
+ * it and try to swap it into place. If it works, or another task beat us
+ * to it with the new value, then update the f_wb_err and return the error
+ * portion. The error at this point must be reported via proper channels
+ * (a'la fsync, or NFS COMMIT operation, etc.).
+ *
+ * While we handle mapping->wb_err with atomic operations, the f_wb_err
+ * value is protected by the f_lock since we must ensure that it reflects
+ * the latest value swapped in for this file descriptor.
+ */
+int file_check_and_advance_wb_err(struct file *file)
+{
+ int err = 0;
+ errseq_t old = READ_ONCE(file->f_wb_err);
+ struct address_space *mapping = file->f_mapping;
+
+ /* Locklessly handle the common case where nothing has changed */
+ if (errseq_check(&mapping->wb_err, old)) {
+ /* Something changed, must use slow path */
+ spin_lock(&file->f_lock);
+ old = file->f_wb_err;
+ err = errseq_check_and_advance(&mapping->wb_err,
+ &file->f_wb_err);
+ trace_file_check_and_advance_wb_err(file, old);
+ spin_unlock(&file->f_lock);
+ }
+ return err;
+}
+EXPORT_SYMBOL(file_check_and_advance_wb_err);
+
+/**
+ * file_write_and_wait_range - write out & wait on a file range
+ * @file: file pointing to address_space with pages
+ * @lstart: offset in bytes where the range starts
+ * @lend: offset in bytes where the range ends (inclusive)
+ *
+ * Write out and wait upon file offsets lstart->lend, inclusive.
+ *
+ * Note that @lend is inclusive (describes the last byte to be written) so
+ * that this function can be used to write to the very end-of-file (end = -1).
+ *
+ * After writing out and waiting on the data, we check and advance the
+ * f_wb_err cursor to the latest value, and return any errors detected there.
+ */
+int file_write_and_wait_range(struct file *file, loff_t lstart, loff_t lend)
+{
+ int err = 0, err2;
+ struct address_space *mapping = file->f_mapping;
+
+ if ((!dax_mapping(mapping) && mapping->nrpages) ||
+ (dax_mapping(mapping) && mapping->nrexceptional)) {
+ err = __filemap_fdatawrite_range(mapping, lstart, lend,
+ WB_SYNC_ALL);
+ /* See comment of filemap_write_and_wait() */
+ if (err != -EIO)
+ __filemap_fdatawait_range(mapping, lstart, lend);
+ }
+ err2 = file_check_and_advance_wb_err(file);
+ if (!err)
+ err = err2;
+ return err;
+}
+EXPORT_SYMBOL(file_write_and_wait_range);
+
/**
* replace_page_cache_page - replace a pagecache page with a new one
* @old: page to be replaced