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mm: don't TestClearPageError in __filemap_fdatawait_range 

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>
This commit is contained in:
Jeff Layton 2017-07-06 07:02:24 -04:00
parent cbeaf9510a
commit 5e8fcc1a0f
1 changed files with 5 additions and 15 deletions
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20
mm/filemap.c
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@ -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);