[PATCH 09/31] aio: try to complete poll iocbs without context switch
From: Christoph Hellwig <hch@lst.de>
Date: 2018-05-22 11:31:57
Also in:
linux-api, linux-fsdevel, lkml
Subsystem:
aio, filesystems (vfs and infrastructure), the rest · Maintainers:
Benjamin LaHaise, Alexander Viro, Christian Brauner, Linus Torvalds
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 4d1eabce6659..85d9102431db 100644
--- a/fs/aio.c
+++ b/fs/aio.c@@ -1632,6 +1632,7 @@ 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);
@@ -1647,9 +1648,22 @@ 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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