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aio: try to complete poll iocbs without context switch 

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>
This commit is contained in:
Christoph Hellwig 2018-05-20 19:19:30 +02:00
parent 2c14fa838c
commit 1962da0d21
1 changed files with 17 additions and 3 deletions
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20
fs/aio.c
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@ -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;
}