[RFC PATCH 1/5] cachefiles: introduce object ondemand state

[Jia Zhu <zhujia.zj@xxxxxxxxxxxxx>]

Previously, @ondemand_id field was used not only to identify ondemand
state of the object, but also to represent the index of the xarray.
This commit introduces @state field to decouple the role of @ondemand_id
and adds helpers to access it.

Signed-off-by: Jia Zhu <zhujia.zj@xxxxxxxxxxxxx>
Reviewed-by: Xin Yin <yinxin.x@xxxxxxxxxxxxx>
---
 fs/cachefiles/internal.h | 33 +++++++++++++++++++++++++++++++++
 fs/cachefiles/ondemand.c | 15 +++++++++------
 2 files changed, 42 insertions(+), 6 deletions(-)

diff --git a/fs/cachefiles/internal.h b/fs/cachefiles/internal.h
index 6cba2c6de2f9..6661b3e361da 100644
--- a/fs/cachefiles/internal.h
+++ b/fs/cachefiles/internal.h
@@ -17,6 +17,7 @@
 #include <linux/security.h>
 #include <linux/xarray.h>
 #include <linux/cachefiles.h>
+#include <linux/atomic.h>
 
 #define CACHEFILES_DIO_BLOCK_SIZE 4096
 
@@ -44,6 +45,11 @@ struct cachefiles_volume {
 	struct dentry			*fanout[256];	/* Fanout subdirs */
 };
 
+enum cachefiles_object_state {
+	CACHEFILES_ONDEMAND_OBJSTATE_close, /* Anonymous fd closed by daemon or initial state */
+	CACHEFILES_ONDEMAND_OBJSTATE_open, /* Anonymous fd associated with object is available */
+};
+
 /*
  * Backing file state.
  */
@@ -62,6 +68,7 @@ struct cachefiles_object {
 #define CACHEFILES_OBJECT_USING_TMPFILE	0		/* Have an unlinked tmpfile */
 #ifdef CONFIG_CACHEFILES_ONDEMAND
 	int				ondemand_id;
+	enum cachefiles_object_state	state;
 #endif
 };
 
@@ -295,6 +302,32 @@ extern void cachefiles_ondemand_clean_object(struct cachefiles_object *object);
 extern int cachefiles_ondemand_read(struct cachefiles_object *object,
 				    loff_t pos, size_t len);
 
+#define CACHEFILES_OBJECT_STATE_FUNCS(_state)	\
+static inline bool								\
+cachefiles_ondemand_object_is_##_state(const struct cachefiles_object *object) \
+{												\
+	/*
+	 * Pairs with smp_store_release() in set_object_##_state()
+	 * I.e. another task can publish state concurrently, by executing
+	 * a RELEASE barrier. We need to use smp_load_acquire() here
+	 * to safely ACQUIRE the memory the other task published.
+	 */											\
+	return smp_load_acquire(&object->state) == CACHEFILES_ONDEMAND_OBJSTATE_##_state; \
+}												\
+												\
+static inline void								\
+cachefiles_ondemand_set_object_##_state(struct cachefiles_object *object) \
+{												\
+	/*
+	 * Pairs with smp_load_acquire() in object_is_##_state()
+	 * I.e. here we publish a state with a RELEASE barrier
+	 * so that concurrent tasks can ACQUIRE it.
+	 */											\
+	smp_store_release(&object->state, CACHEFILES_ONDEMAND_OBJSTATE_##_state); \
+}
+
+CACHEFILES_OBJECT_STATE_FUNCS(open);
+CACHEFILES_OBJECT_STATE_FUNCS(close);
 #else
 static inline ssize_t cachefiles_ondemand_daemon_read(struct cachefiles_cache *cache,
 					char __user *_buffer, size_t buflen)
diff --git a/fs/cachefiles/ondemand.c b/fs/cachefiles/ondemand.c
index 1fee702d5529..e3155a5f32e4 100644
--- a/fs/cachefiles/ondemand.c
+++ b/fs/cachefiles/ondemand.c
@@ -15,6 +15,7 @@ static int cachefiles_ondemand_fd_release(struct inode *inode,
 
 	xa_lock(&cache->reqs);
 	object->ondemand_id = CACHEFILES_ONDEMAND_ID_CLOSED;
+	cachefiles_ondemand_set_object_close(object);
 
 	/*
 	 * Flush all pending READ requests since their completion depends on
@@ -172,6 +173,8 @@ int cachefiles_ondemand_copen(struct cachefiles_cache *cache, char *args)
 		set_bit(FSCACHE_COOKIE_NO_DATA_TO_READ, &cookie->flags);
 	trace_cachefiles_ondemand_copen(req->object, id, size);
 
+	cachefiles_ondemand_set_object_open(req->object);
+
 out:
 	complete(&req->done);
 	return ret;
@@ -353,7 +356,8 @@ static int cachefiles_ondemand_send_req(struct cachefiles_object *object,
 		/* coupled with the barrier in cachefiles_flush_reqs() */
 		smp_mb();
 
-		if (opcode != CACHEFILES_OP_OPEN && object->ondemand_id <= 0) {
+		if (opcode != CACHEFILES_OP_OPEN &&
+			!cachefiles_ondemand_object_is_open(object)) {
 			WARN_ON_ONCE(object->ondemand_id == 0);
 			xas_unlock(&xas);
 			ret = -EIO;
@@ -420,7 +424,6 @@ static int cachefiles_ondemand_init_close_req(struct cachefiles_req *req,
 					      void *private)
 {
 	struct cachefiles_object *object = req->object;
-	int object_id = object->ondemand_id;
 
 	/*
 	 * It's possible that object id is still 0 if the cookie looking up
@@ -428,10 +431,10 @@ static int cachefiles_ondemand_init_close_req(struct cachefiles_req *req,
 	 * sending CLOSE request for CACHEFILES_ONDEMAND_ID_CLOSED, which means
 	 * anon_fd has already been closed.
 	 */
-	if (object_id <= 0)
+	if (!cachefiles_ondemand_object_is_open(object))
 		return -ENOENT;
 
-	req->msg.object_id = object_id;
+	req->msg.object_id = object->ondemand_id;
 	trace_cachefiles_ondemand_close(object, &req->msg);
 	return 0;
 }
@@ -450,7 +453,7 @@ static int cachefiles_ondemand_init_read_req(struct cachefiles_req *req,
 	int object_id = object->ondemand_id;
 
 	/* Stop enqueuing requests when daemon has closed anon_fd. */
-	if (object_id <= 0) {
+	if (!cachefiles_ondemand_object_is_open(object)) {
 		WARN_ON_ONCE(object_id == 0);
 		pr_info_once("READ: anonymous fd closed prematurely.\n");
 		return -EIO;
@@ -475,7 +478,7 @@ int cachefiles_ondemand_init_object(struct cachefiles_object *object)
 	 * creating a new tmpfile as the cache file. Reuse the previously
 	 * allocated object ID if any.
 	 */
-	if (object->ondemand_id > 0)
+	if (cachefiles_ondemand_object_is_open(object))
 		return 0;
 
 	volume_key_size = volume->key[0] + 1;
-- 
2.20.1