[PATCH v1 14/30] io_uring: add release callback for ring death

[Joanne Koong <joannelkoong@gmail.com>]

Allow registering a release callback on a ring context that will be
called when the ring is about to be destroyed.

This is a preparatory patch for fuse. Fuse will be pinning buffers and
registering bvecs, which requires cleanup whenever a server
disconnects. It needs to know if the ring is alive when the server has
disconnected, to avoid double-freeing or accessing invalid memory.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
 include/linux/io_uring.h       |  9 +++++++++
 include/linux/io_uring_types.h |  2 ++
 io_uring/io_uring.c            | 15 +++++++++++++++
 3 files changed, 26 insertions(+)

diff --git a/include/linux/io_uring.h b/include/linux/io_uring.h
index 85fe4e6b275c..327fd8ac6e42 100644
--- a/include/linux/io_uring.h
+++ b/include/linux/io_uring.h
@@ -2,6 +2,7 @@
 #ifndef _LINUX_IO_URING_H
 #define _LINUX_IO_URING_H
 
+#include <linux/io_uring_types.h>
 #include <linux/sched.h>
 #include <linux/xarray.h>
 #include <uapi/linux/io_uring.h>
@@ -28,6 +29,9 @@ static inline void io_uring_free(struct task_struct *tsk)
 	if (tsk->io_uring)
 		__io_uring_free(tsk);
 }
+void io_uring_set_release_callback(struct io_ring_ctx *ctx,
+				   void (*release)(void *), void *priv,
+				   unsigned int issue_flags);
 #else
 static inline void io_uring_task_cancel(void)
 {
@@ -46,6 +50,11 @@ static inline bool io_is_uring_fops(struct file *file)
 {
 	return false;
 }
+static inline void
+io_uring_set_release_callback(struct io_ring_ctx *ctx, void (*release)(void *),
+			      void *priv, unsigned int issue_flags)
+{
+}
 #endif
 
 #endif
diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
index dcc95e73f12f..67c66658e3ec 100644
--- a/include/linux/io_uring_types.h
+++ b/include/linux/io_uring_types.h
@@ -441,6 +441,8 @@ struct io_ring_ctx {
 	struct work_struct		exit_work;
 	struct list_head		tctx_list;
 	struct completion		ref_comp;
+	void				(*release)(void *);
+	void				*priv;
 
 	/* io-wq management, e.g. thread count */
 	u32				iowq_limits[2];
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 1e58fc1d5667..04ffcfa6f2d6 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -2952,6 +2952,19 @@ static __poll_t io_uring_poll(struct file *file, poll_table *wait)
 	return mask;
 }
 
+void io_uring_set_release_callback(struct io_ring_ctx *ctx,
+				   void (*release)(void *), void *priv,
+				   unsigned int issue_flags)
+{
+	io_ring_submit_lock(ctx, issue_flags);
+
+	ctx->release = release;
+	ctx->priv = priv;
+
+	io_ring_submit_unlock(ctx, issue_flags);
+}
+EXPORT_SYMBOL_GPL(io_uring_set_release_callback);
+
 struct io_tctx_exit {
 	struct callback_head		task_work;
 	struct completion		completion;
@@ -3099,6 +3112,8 @@ static int io_uring_release(struct inode *inode, struct file *file)
 	struct io_ring_ctx *ctx = file->private_data;
 
 	file->private_data = NULL;
+	if (ctx->release)
+		ctx->release(ctx->priv);
 	io_ring_ctx_wait_and_kill(ctx);
 	return 0;
 }
-- 
2.47.3