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Subject[RFC 4/5] dio: remove duplicate bio wait code
Date
dio: remove duplicate bio wait code

Now that we have a single refcount and waiting path we can reuse it in the
async 'should_wait' path. It continues to rely on the fragile link between the
conditional in dio_complete_aio() which decides to complete the AIO and the
conditional in direct_io_worker() which decides to wait and free.

By waiting before dropping the reference we stop dio_bio_end_aio() from calling
dio_complete_aio() which used to wake up the waiter after seeing the reference
count drop to 0. We hoist this wake up into dio_bio_end_aio() which now
notices when it's left a single remaining reference that is held by the waiter.

Signed-off-by: Zach Brown <zach.brown@oracle.com>
---

fs/direct-io.c | 41 ++++++++++++-----------------------------
1 file changed, 12 insertions(+), 29 deletions(-)

Index: 2.6.18-rc6-dio-cleanup/fs/direct-io.c
===================================================================
--- 2.6.18-rc6-dio-cleanup.orig/fs/direct-io.c
+++ 2.6.18-rc6-dio-cleanup/fs/direct-io.c
@@ -256,7 +256,6 @@ static int dio_complete(struct dio *dio,
*/
static void dio_complete_aio(struct dio *dio)
{
- unsigned long flags;
int ret;

ret = dio_complete(dio, dio->iocb->ki_pos, 0);
@@ -266,14 +265,6 @@ static void dio_complete_aio(struct dio
((dio->rw == READ) && dio->result)) {
aio_complete(dio->iocb, ret, 0);
kfree(dio);
- } else {
- /*
- * Falling back to buffered
- */
- spin_lock_irqsave(&dio->bio_lock, flags);
- if (dio->waiter)
- wake_up_process(dio->waiter);
- spin_unlock_irqrestore(&dio->bio_lock, flags);
}
}

@@ -284,6 +275,8 @@ static int dio_bio_complete(struct dio *
static int dio_bio_end_aio(struct bio *bio, unsigned int bytes_done, int error)
{
struct dio *dio = bio->bi_private;
+ int waiter_holds_ref = 0;
+ int remaining;

if (bio->bi_size)
return 1;
@@ -291,7 +284,12 @@ static int dio_bio_end_aio(struct bio *b
/* cleanup the bio */
dio_bio_complete(dio, bio);

- if (atomic_dec_and_test(&dio->refcount))
+ waiter_holds_ref = !!dio->waiter;
+ remaining = atomic_sub_return(1, (&dio->refcount));
+ if (remaining == 1 && waiter_holds_ref)
+ wake_up_process(dio->waiter);
+
+ if (remaining == 0)
dio_complete_aio(dio);

return 0;
@@ -1089,30 +1087,15 @@ direct_io_worker(int rw, struct kiocb *i
if (ret == 0)
ret = dio->result;

+ if (should_wait)
+ dio_await_completion(dio);
+
/* this can free the dio */
if (atomic_dec_and_test(&dio->refcount))
dio_complete_aio(dio);

- if (should_wait) {
- unsigned long flags;
- /*
- * Wait for already issued I/O to drain out and
- * release its references to user-space pages
- * before returning to fallback on buffered I/O
- */
-
- spin_lock_irqsave(&dio->bio_lock, flags);
- set_current_state(TASK_UNINTERRUPTIBLE);
- while (atomic_read(&dio->refcount)) {
- spin_unlock_irqrestore(&dio->bio_lock, flags);
- io_schedule();
- spin_lock_irqsave(&dio->bio_lock, flags);
- set_current_state(TASK_UNINTERRUPTIBLE);
- }
- spin_unlock_irqrestore(&dio->bio_lock, flags);
- set_current_state(TASK_RUNNING);
+ if (should_wait)
kfree(dio);
- }
} else {
dio_await_completion(dio);

-
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