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From: Naoya Horiguchi on 12 Aug 2010 04:10
Basically it is user's responsibility to take care of race condition
related to direct I/O, but some events which are out of user's control
(such as memory failure) can happen at any time. So we need to lock and
set/clear PG_writeback flags in dierct I/O code to protect from data loss.

Signed-off-by: Naoya Horiguchi <n-horiguchi(a)ah.jp.nec.com>
---
fs/direct-io.c | 8 +++++++-
1 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index 7600aac..0d0810d 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -439,7 +439,10 @@ static int dio_bio_complete(struct dio *dio, struct bio *bio)
struct page *page = bvec[page_no].bv_page;

if (dio->rw == READ && !PageCompound(page))
- set_page_dirty_lock(page);
+ set_page_dirty(page);
+ if (dio->rw & WRITE)
+ end_page_writeback(page);
+ unlock_page(page);
page_cache_release(page);
}
bio_put(bio);
@@ -702,11 +705,14 @@ submit_page_section(struct dio *dio, struct page *page,
{
int ret = 0;

+ lock_page(page);
+
if (dio->rw & WRITE) {
/*
* Read accounting is performed in submit_bio()
*/
task_io_account_write(len);
+ set_page_writeback(page);
}

/*
--
1.7.2.1

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