[PATCH v3 16/20] mm: don't TestClearPageError in __filemap_fdatawait_range

Jeff Layton
2017-04-24T13:24:37Z

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 on the box at the wrong
time 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 | 19 +++++--------------
1 file changed, 5 insertions(+), 14 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index d94a76d4e023..47e7f50fb830 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -363,17 +363,16 @@ 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) &&
@@ -390,14 +389,11 @@ 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;
}

/**
@@ -417,15 +413,10 @@ 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;
errseq_t since = filemap_sample_wb_error(mapping);

- ret = __filemap_fdatawait_range(mapping, start_byte, end_byte);
- ret2 = filemap_check_wb_error(mapping, since);
- if (!ret)
- ret = ret2;
-
- return ret;
+ __filemap_fdatawait_range(mapping, start_byte, end_byte);
+ return filemap_check_wb_error(mapping, since);
}
EXPORT_SYMBOL(filemap_fdatawait_range);

--
2.9.3