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From: jlayton@kernel.org
To: Andrew Morton <akpm@linux-foundation.org>,
	Al Viro <viro@ZenIV.linux.org.uk>, Jan Kara <jack@suse.cz>,
	tytso@mit.edu, axboe@kernel.dk, mawilcox@microsoft.com,
	ross.zwisler@linux.intel.com, corbet@lwn.net,
	Chris Mason <clm@fb.com>, Josef Bacik <jbacik@fb.com>,
	David Sterba <dsterba@suse.com>,
	"Darrick J . Wong" <darrick.wong@oracle.com>
Cc: Carlos Maiolino <cmaiolino@redhat.com>,
	Eryu Guan <eguan@redhat.com>, David Howells <dhowells@redhat.com>,
	Christoph Hellwig <hch@infradead.org>,
	Liu Bo <bo.li.liu@oracle.com>,
	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
Subject: [PATCH v8 07/18] mm: don't TestClearPageError in __filemap_fdatawait_range
Date: Thu, 29 Jun 2017 09:19:43 -0400
Message-ID: <20170629131954.28733-8-jlayton@kernel.org> (raw)
In-Reply-To: <20170629131954.28733-1-jlayton@kernel.org>

From: Jeff Layton <jlayton@redhat.com>

The -EIO returned here can end up overriding whatever error is marked in
the address space, and be returned at fsync time, even when there is a
more appropriate error stored in the mapping.

Read errors are also sometimes tracked on a per-page level using
PG_error. Suppose we have a read error on a page, and then that page is
subsequently dirtied by overwriting the whole page. Writeback doesn't
clear PG_error, so we can then end up successfully writing back that
page and still return -EIO on fsync.

Worse yet, PG_error is cleared during a sync() syscall, but the -EIO
return from that is silently discarded. Any subsystem that is relying on
PG_error to report errors during fsync can easily lose writeback errors
due to this. All you need is a stray sync() call to wait for writeback
to complete and you've lost the error.

Since the handling of the PG_error flag is somewhat inconsistent across
subsystems, let's just rely on marking the address space when there are
writeback errors. Change the TestClearPageError call to ClearPageError,
and make __filemap_fdatawait_range a void return function.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 mm/filemap.c | 20 +++++---------------
 1 file changed, 5 insertions(+), 15 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 49bc9720fb00..eb99b5f23c61 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -386,17 +386,16 @@ int filemap_flush(struct address_space *mapping)
 }
 EXPORT_SYMBOL(filemap_flush);
 
-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) &&
@@ -413,14 +412,11 @@ 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;
 }
 
 /**
@@ -440,14 +436,8 @@ static int __filemap_fdatawait_range(struct address_space *mapping,
 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);
 
-- 
2.13.0

  parent reply index

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-06-29 13:19 [PATCH v8 00/18] fs: enhanced writeback error reporting with errseq_t (pile #1) jlayton
2017-06-29 13:19 ` [PATCH v8 01/18] fs: remove call_fsync helper function jlayton
2017-06-29 13:19 ` [PATCH v8 02/18] buffer: use mapping_set_error instead of setting the flag jlayton
2017-06-29 13:19 ` [PATCH v8 03/18] fs: check for writeback errors after syncing out buffers in generic_file_fsync jlayton
2017-06-29 14:19   ` Christoph Hellwig
2017-06-29 20:17     ` Jeff Layton
2017-06-29 13:19 ` [PATCH v8 04/18] buffer: set errors in mapping at the time that the error occurs jlayton
2017-06-29 13:19 ` [PATCH v8 05/18] jbd2: don't clear and reset errors after waiting on writeback jlayton
2017-06-29 13:19 ` [PATCH v8 06/18] mm: clear AS_EIO/AS_ENOSPC when writeback initiation fails jlayton
2017-06-29 13:19 ` jlayton [this message]
2017-06-29 13:19 ` [PATCH v8 08/18] mm: clean up error handling in write_one_page jlayton
2017-06-29 13:19 ` [PATCH v8 09/18] lib: add errseq_t type and infrastructure for handling it jlayton
2017-06-29 13:19 ` [PATCH v8 10/18] fs: new infrastructure for writeback error handling and reporting jlayton
2017-06-29 13:45   ` Jeff Layton
2017-06-29 17:52   ` Jeff Layton
2017-06-29 13:19 ` [PATCH v8 11/18] mm: set both AS_EIO/AS_ENOSPC and errseq_t in mapping_set_error jlayton
2017-06-29 13:19 ` [PATCH v8 12/18] Documentation: flesh out the section in vfs.txt on storing and reporting writeback errors jlayton
2017-06-29 17:11   ` Darrick J. Wong
2017-06-29 18:13     ` Jeff Layton
2017-06-29 18:21       ` Matthew Wilcox
2017-06-29 20:42         ` Jeff Layton
2017-06-29 13:19 ` [PATCH v8 13/18] dax: set errors in mapping when writeback fails jlayton
2017-06-29 13:19 ` [PATCH v8 14/18] block: convert to errseq_t based writeback error tracking jlayton
2017-06-29 14:18   ` Christoph Hellwig
2017-06-29 13:19 ` [PATCH v8 15/18] fs: convert __generic_file_fsync to use errseq_t based reporting jlayton
2017-06-29 13:19 ` [PATCH v8 16/18] ext4: use errseq_t based error handling for reporting data writeback errors jlayton
2017-06-29 14:12   ` Christoph Hellwig
2017-06-29 20:26     ` Jeff Layton
2017-06-29 13:19 ` [PATCH v8 17/18] xfs: minimal conversion to errseq_t writeback error reporting jlayton
2017-06-29 14:12   ` Christoph Hellwig
2017-06-30 16:45     ` Jeff Layton
2017-06-30 16:49       ` Christoph Hellwig
2017-06-29 17:13   ` Darrick J. Wong
2017-06-29 13:19 ` [PATCH v8 18/18] btrfs: minimal conversion to errseq_t writeback error reporting on fsync jlayton
2017-06-29 14:17   ` Christoph Hellwig
2017-06-29 20:32     ` Jeff Layton

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