io_uring: replace workqueue usage with io-wq

Drop various work-arounds we have for workqueues:

- We no longer need the async_list for tracking sequential IO.

- We don't have to maintain our own mm tracking/setting.

- We don't need a separate workqueue for buffered writes. This didn't
  even work that well to begin with, as it was suboptimal for multiple
  buffered writers on multiple files.

- We can properly cancel pending interruptible work. This fixes
  deadlocks with particularly socket IO, where we cannot cancel them
  when the io_uring is closed. Hence the ring will wait forever for
  these requests to complete, which may never happen. This is different
  from disk IO where we know requests will complete in a finite amount
  of time.

- Due to being able to cancel work interruptible work that is already
  running, we can implement file table support for work. We need that
  for supporting system calls that add to a process file table.

- It gets us one step closer to adding async support for any system
  call.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/trace/events/io_uring.h

@@ -7,6 +7,8 @@
 
 #include <linux/tracepoint.h>
 
+struct io_wq_work;
+
 /**
  * io_uring_create - called after a new io_uring context was prepared
  *
@@ -126,15 +128,15 @@ TRACE_EVENT(io_uring_file_get,
  * io_uring_queue_async_work - called before submitting a new async work
  *
  * @ctx:	pointer to a ring context structure
- * @rw:		type of workqueue, normal or buffered writes
+ * @hashed:	type of workqueue, hashed or normal
  * @req:	pointer to a submitted request
- * @work:	pointer to a submitted work_struct
+ * @work:	pointer to a submitted io_wq_work
  *
  * Allows to trace asynchronous work submission.
  */
 TRACE_EVENT(io_uring_queue_async_work,
 
-	TP_PROTO(void *ctx, int rw, void * req, struct work_struct *work,
+	TP_PROTO(void *ctx, int rw, void * req, struct io_wq_work *work,
 			 unsigned int flags),
 
 	TP_ARGS(ctx, rw, req, work, flags),
@@ -143,7 +145,7 @@ TRACE_EVENT(io_uring_queue_async_work,
 		__field(  void *,				ctx		)
 		__field(  int,					rw		)
 		__field(  void *,				req		)
-		__field(  struct work_struct *,	work	)
+		__field(  struct io_wq_work *,		work	)
 		__field(  unsigned int,			flags	)
 	),
 
@@ -157,7 +159,7 @@ TRACE_EVENT(io_uring_queue_async_work,
 
 	TP_printk("ring %p, request %p, flags %d, %s queue, work %p",
 			  __entry->ctx, __entry->req, __entry->flags,
-			  __entry->rw ? "buffered" : "normal", __entry->work)
+			  __entry->rw ? "hashed" : "normal", __entry->work)
 );
 
 /**

init/Kconfig

@@ -1548,6 +1548,7 @@ config AIO
 config IO_URING
 	bool "Enable IO uring support" if EXPERT
 	select ANON_INODES
+	select IO_WQ
 	default y
 	help
 	  This option enables support for the io_uring interface, enabling