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Subject[PATCH] VFS mpage.c:mpage_end_io_read wrong behavior when I/O failure occurs
Related FS:

Related files:

Bug description:
Make a partition in USB storage HDD, create a test file with
any contents.
Write a program, do: open(O_RDWR) - write - fsync - close.
After each operation, pause for a while, such as 3 seconds. Between
open and fsync, unplug USB wire to force an I/O error. fsync will
return OK instead of EIO.

Bug analysis:
sys_fsync does 3 jobs:
1)submit all pages taged with PAGECACHE_TAG_DIRTY to disk I/O,
2)do file-system related fsync operations
3)wait all pages taged with PAGECACHE_TAG_WRITEBACK to complete.
Here, all disk I/O are asynchronous, when finished, mpage_end_io_write
will remove page from mapping's PAGECACHE_TAG_WRITEBACK tree. If I/O
fails, it will also set PG_error flag, but it FORGET to set the
mapping->flags AS_EIO flag. So in step 3, sys_fsync won't notice these
pages, then no error returns.
static int mpage_end_io_write(...)
if (!uptodate)
SetPageError(page);<-- Not set mapping->flags

static int wait_on_page_writeback_range(struct address_space *mapping,
pgoff_t start, pgoff_t end)
int ret = 0;

while ((index <= end) && <-- For I/O error page, no loop here
(nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1)) != 0) {

if (test_and_clear_bit(AS_ENOSPC, &mapping->flags))
ret = -ENOSPC;
if (test_and_clear_bit(AS_EIO, &mapping->flags)) <-- Not set
ret = -EIO;

return ret; <-- return 0

Way around:
Set AS_EIO to mapping->flags if I/O error happens.

diff -uNp linux- linux-
--- linux- 2005-05-27 01:06:46.000000000 -0400
+++ linux- 2005-06-02 14:29:42.264334920 -0400
@@ -79,8 +79,11 @@ static int mpage_end_io_write(struct bio
if (--bvec >= bio->bi_io_vec)

- if (!uptodate)
+ if (!uptodate){
+ if(page->mapping)
+ set_bit(AS_EIO, &page->mapping->flags);
+ }
} while (bvec >= bio->bi_io_vec);

Signed-off-by: Qu Fuping<>

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