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Subject[PATCH 11/33] aio: try to complete poll iocbs without context switch
Date
If we can acquire ctx_lock without spinning we can just remove our
iocb from the active_reqs list, and thus complete the iocbs from the
wakeup context.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
fs/aio.c | 20 +++++++++++++++++---
1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index bd711cfa4a1f..8274d09d44a2 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1633,6 +1633,7 @@ static int aio_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
void *key)
{
struct poll_iocb *req = container_of(wait, struct poll_iocb, wait);
+ struct aio_kiocb *iocb = container_of(req, struct aio_kiocb, poll);
struct file *file = req->file;
__poll_t mask = key_to_poll(key);

@@ -1648,9 +1649,22 @@ static int aio_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,

__aio_poll_remove(req);

- req->events = mask;
- INIT_WORK(&req->work, aio_poll_work);
- schedule_work(&req->work);
+ /*
+ * Try completing without a context switch if we can acquire ctx_lock
+ * without spinning. Otherwise we need to defer to a workqueue to
+ * avoid a deadlock due to the lock order.
+ */
+ if (spin_trylock(&iocb->ki_ctx->ctx_lock)) {
+ list_del_init(&iocb->ki_list);
+ spin_unlock(&iocb->ki_ctx->ctx_lock);
+
+ __aio_poll_complete(req, mask);
+ } else {
+ req->events = mask;
+ INIT_WORK(&req->work, aio_poll_work);
+ schedule_work(&req->work);
+ }
+
return 1;
}

--
2.17.0
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