io_uring/alloc_cache: switch to array based caching

Currently lists are being used to manage this, but best practice is
usually to have these in an array instead as that it cheaper to manage.

Outside of that detail, games are also played with KASAN as the list
is inside the cached entry itself.

Finally, all users of this need a struct io_cache_entry embedded in
their struct, which is union'ized with something else in there that
isn't used across the free -> realloc cycle.

Get rid of all of that, and simply have it be an array. This will not
change the memory used, as we're just trading an 8-byte member entry
for the per-elem array size.

This reduces the overhead of the recycled allocations, and it reduces
the amount of code code needed to support recycling to about half of
what it currently is.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/io_uring_types.h

@@ -220,7 +220,7 @@ struct io_ev_fd {
 };
 
 struct io_alloc_cache {
-	struct io_wq_work_node	list;
+	void			**entries;
 	unsigned int		nr_cached;
 	unsigned int		max_cached;
 	size_t			elem_size;

io_uring/alloc_cache.h

@@ -6,61 +6,56 @@
  */
 #define IO_ALLOC_CACHE_MAX	128
 
-struct io_cache_entry {
-	struct io_wq_work_node node;
-};
-
 static inline bool io_alloc_cache_put(struct io_alloc_cache *cache,
-				      struct io_cache_entry *entry)
+				      void *entry)
 {
 	if (cache->nr_cached < cache->max_cached) {
-		cache->nr_cached++;
+		if (!kasan_mempool_poison_object(entry))
-		wq_stack_add_head(&entry->node, &cache->list);
+			return false;
-		kasan_mempool_poison_object(entry);
+		cache->entries[cache->nr_cached++] = entry;
 		return true;
 	}
 	return false;
 }
 
-static inline bool io_alloc_cache_empty(struct io_alloc_cache *cache)
+static inline void *io_alloc_cache_get(struct io_alloc_cache *cache)
 {
-	return !cache->list.next;
+	if (cache->nr_cached) {
-}
+		void *entry = cache->entries[--cache->nr_cached];
 
-static inline struct io_cache_entry *io_alloc_cache_get(struct io_alloc_cache *cache)
-{
-	if (cache->list.next) {
-		struct io_cache_entry *entry;
-
-		entry = container_of(cache->list.next, struct io_cache_entry, node);
 		kasan_mempool_unpoison_object(entry, cache->elem_size);
-		cache->list.next = cache->list.next->next;
-		cache->nr_cached--;
 		return entry;
 	}
 
 	return NULL;
 }
 
-static inline void io_alloc_cache_init(struct io_alloc_cache *cache,
+/* returns false if the cache was initialized properly */
+static inline bool io_alloc_cache_init(struct io_alloc_cache *cache,
 				       unsigned max_nr, size_t size)
 {
-	cache->list.next = NULL;
+	cache->entries = kvmalloc_array(max_nr, sizeof(void *), GFP_KERNEL);
-	cache->nr_cached = 0;
+	if (cache->entries) {
-	cache->max_cached = max_nr;
+		cache->nr_cached = 0;
-	cache->elem_size = size;
+		cache->max_cached = max_nr;
+		cache->elem_size = size;
+		return false;
+	}
+	return true;
 }
 
 static inline void io_alloc_cache_free(struct io_alloc_cache *cache,
-					void (*free)(struct io_cache_entry *))
+				       void (*free)(const void *))
 {
-	while (1) {
+	void *entry;
-		struct io_cache_entry *entry = io_alloc_cache_get(cache);
 
-		if (!entry)
+	if (!cache->entries)
-			break;
+		return;
+
+	while ((entry = io_alloc_cache_get(cache)) != NULL)
 		free(entry);
-	}
+
-	cache->nr_cached = 0;
+	kvfree(cache->entries);
+	cache->entries = NULL;
 }
 #endif

io_uring/futex.c

@@ -9,7 +9,7 @@
 
 #include "../kernel/futex/futex.h"
 #include "io_uring.h"
-#include "rsrc.h"
+#include "alloc_cache.h"
 #include "futex.h"
 
 struct io_futex {
@@ -27,27 +27,21 @@ struct io_futex {
 };
 
 struct io_futex_data {
-	union {
+	struct futex_q	q;
-		struct futex_q		q;
-		struct io_cache_entry	cache;
-	};
 	struct io_kiocb	*req;
 };
 
-void io_futex_cache_init(struct io_ring_ctx *ctx)
+#define IO_FUTEX_ALLOC_CACHE_MAX	32
-{
-	io_alloc_cache_init(&ctx->futex_cache, IO_NODE_ALLOC_CACHE_MAX,
-				sizeof(struct io_futex_data));
-}
 
-static void io_futex_cache_entry_free(struct io_cache_entry *entry)
+bool io_futex_cache_init(struct io_ring_ctx *ctx)
 {
-	kfree(container_of(entry, struct io_futex_data, cache));
+	return io_alloc_cache_init(&ctx->futex_cache, IO_FUTEX_ALLOC_CACHE_MAX,
+				sizeof(struct io_futex_data));
 }
 
 void io_futex_cache_free(struct io_ring_ctx *ctx)
 {
-	io_alloc_cache_free(&ctx->futex_cache, io_futex_cache_entry_free);
+	io_alloc_cache_free(&ctx->futex_cache, kfree);
 }
 
 static void __io_futex_complete(struct io_kiocb *req, struct io_tw_state *ts)
@@ -63,7 +57,7 @@ static void io_futex_complete(struct io_kiocb *req, struct io_tw_state *ts)
 	struct io_ring_ctx *ctx = req->ctx;
 
 	io_tw_lock(ctx, ts);
-	if (!io_alloc_cache_put(&ctx->futex_cache, &ifd->cache))
+	if (!io_alloc_cache_put(&ctx->futex_cache, ifd))
 		kfree(ifd);
 	__io_futex_complete(req, ts);
 }
@@ -259,11 +253,11 @@ static void io_futex_wake_fn(struct wake_q_head *wake_q, struct futex_q *q)
 
 static struct io_futex_data *io_alloc_ifd(struct io_ring_ctx *ctx)
 {
-	struct io_cache_entry *entry;
+	struct io_futex_data *ifd;
 
-	entry = io_alloc_cache_get(&ctx->futex_cache);
+	ifd = io_alloc_cache_get(&ctx->futex_cache);
-	if (entry)
+	if (ifd)
-		return container_of(entry, struct io_futex_data, cache);
+		return ifd;
 
 	return kmalloc(sizeof(struct io_futex_data), GFP_NOWAIT);
 }

io_uring/futex.h

@@ -13,7 +13,7 @@ int io_futex_cancel(struct io_ring_ctx *ctx, struct io_cancel_data *cd,
 		    unsigned int issue_flags);
 bool io_futex_remove_all(struct io_ring_ctx *ctx, struct task_struct *task,
 			 bool cancel_all);
-void io_futex_cache_init(struct io_ring_ctx *ctx);
+bool io_futex_cache_init(struct io_ring_ctx *ctx);
 void io_futex_cache_free(struct io_ring_ctx *ctx);
 #else
 static inline int io_futex_cancel(struct io_ring_ctx *ctx,
@@ -27,8 +27,9 @@ static inline bool io_futex_remove_all(struct io_ring_ctx *ctx,
 {
 	return false;
 }
-static inline void io_futex_cache_init(struct io_ring_ctx *ctx)
+static inline bool io_futex_cache_init(struct io_ring_ctx *ctx)
 {
+	return false;
 }
 static inline void io_futex_cache_free(struct io_ring_ctx *ctx)
 {

io_uring/io_uring.c

@@ -276,6 +276,7 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 {
 	struct io_ring_ctx *ctx;
 	int hash_bits;
+	bool ret;
 
 	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
 	if (!ctx)
@@ -305,17 +306,19 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 	INIT_LIST_HEAD(&ctx->cq_overflow_list);
 	INIT_LIST_HEAD(&ctx->io_buffers_cache);
 	INIT_HLIST_HEAD(&ctx->io_buf_list);
-	io_alloc_cache_init(&ctx->rsrc_node_cache, IO_NODE_ALLOC_CACHE_MAX,
+	ret = io_alloc_cache_init(&ctx->rsrc_node_cache, IO_NODE_ALLOC_CACHE_MAX,
 			    sizeof(struct io_rsrc_node));
-	io_alloc_cache_init(&ctx->apoll_cache, IO_ALLOC_CACHE_MAX,
+	ret |= io_alloc_cache_init(&ctx->apoll_cache, IO_ALLOC_CACHE_MAX,
 			    sizeof(struct async_poll));
-	io_alloc_cache_init(&ctx->netmsg_cache, IO_ALLOC_CACHE_MAX,
+	ret |= io_alloc_cache_init(&ctx->netmsg_cache, IO_ALLOC_CACHE_MAX,
 			    sizeof(struct io_async_msghdr));
-	io_alloc_cache_init(&ctx->rw_cache, IO_ALLOC_CACHE_MAX,
+	ret |= io_alloc_cache_init(&ctx->rw_cache, IO_ALLOC_CACHE_MAX,
 			    sizeof(struct io_async_rw));
-	io_alloc_cache_init(&ctx->uring_cache, IO_ALLOC_CACHE_MAX,
+	ret |= io_alloc_cache_init(&ctx->uring_cache, IO_ALLOC_CACHE_MAX,
 			    sizeof(struct uring_cache));
-	io_futex_cache_init(ctx);
+	ret |= io_futex_cache_init(ctx);
+	if (ret)
+		goto err;
 	init_completion(&ctx->ref_comp);
 	xa_init_flags(&ctx->personalities, XA_FLAGS_ALLOC1);
 	mutex_init(&ctx->uring_lock);
@@ -345,6 +348,12 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 
 	return ctx;
 err:
+	io_alloc_cache_free(&ctx->rsrc_node_cache, kfree);
+	io_alloc_cache_free(&ctx->apoll_cache, kfree);
+	io_alloc_cache_free(&ctx->netmsg_cache, io_netmsg_cache_free);
+	io_alloc_cache_free(&ctx->rw_cache, io_rw_cache_free);
+	io_alloc_cache_free(&ctx->uring_cache, kfree);
+	io_futex_cache_free(ctx);
 	kfree(ctx->cancel_table.hbs);
 	kfree(ctx->cancel_table_locked.hbs);
 	xa_destroy(&ctx->io_bl_xa);
@@ -1482,7 +1491,7 @@ static void io_free_batch_list(struct io_ring_ctx *ctx,
 
 				if (apoll->double_poll)
 					kfree(apoll->double_poll);
-				if (!io_alloc_cache_put(&ctx->apoll_cache, &apoll->cache))
+				if (!io_alloc_cache_put(&ctx->apoll_cache, apoll))
 					kfree(apoll);
 				req->flags &= ~REQ_F_POLLED;
 			}
@@ -2778,11 +2787,6 @@ static void io_req_caches_free(struct io_ring_ctx *ctx)
 	mutex_unlock(&ctx->uring_lock);
 }
 
-static void io_rsrc_node_cache_free(struct io_cache_entry *entry)
-{
-	kfree(container_of(entry, struct io_rsrc_node, cache));
-}
-
 static __cold void io_ring_ctx_free(struct io_ring_ctx *ctx)
 {
 	io_sq_thread_finish(ctx);
@@ -2797,10 +2801,10 @@ static __cold void io_ring_ctx_free(struct io_ring_ctx *ctx)
 		__io_sqe_files_unregister(ctx);
 	io_cqring_overflow_kill(ctx);
 	io_eventfd_unregister(ctx);
-	io_alloc_cache_free(&ctx->apoll_cache, io_apoll_cache_free);
+	io_alloc_cache_free(&ctx->apoll_cache, kfree);
 	io_alloc_cache_free(&ctx->netmsg_cache, io_netmsg_cache_free);
 	io_alloc_cache_free(&ctx->rw_cache, io_rw_cache_free);
-	io_alloc_cache_free(&ctx->uring_cache, io_uring_cache_free);
+	io_alloc_cache_free(&ctx->uring_cache, kfree);
 	io_futex_cache_free(ctx);
 	io_destroy_buffers(ctx);
 	mutex_unlock(&ctx->uring_lock);
@@ -2816,7 +2820,7 @@ static __cold void io_ring_ctx_free(struct io_ring_ctx *ctx)
 	WARN_ON_ONCE(!list_empty(&ctx->rsrc_ref_list));
 	WARN_ON_ONCE(!list_empty(&ctx->ltimeout_list));
 
-	io_alloc_cache_free(&ctx->rsrc_node_cache, io_rsrc_node_cache_free);
+	io_alloc_cache_free(&ctx->rsrc_node_cache, kfree);
 	if (ctx->mm_account) {
 		mmdrop(ctx->mm_account);
 		ctx->mm_account = NULL;

io_uring/net.c

@@ -137,7 +137,7 @@ static void io_netmsg_recycle(struct io_kiocb *req, unsigned int issue_flags)
 
 	/* Let normal cleanup path reap it if we fail adding to the cache */
 	iov = hdr->free_iov;
-	if (io_alloc_cache_put(&req->ctx->netmsg_cache, &hdr->cache)) {
+	if (io_alloc_cache_put(&req->ctx->netmsg_cache, hdr)) {
 		if (iov)
 			kasan_mempool_poison_object(iov);
 		req->async_data = NULL;
@@ -148,12 +148,10 @@ static void io_netmsg_recycle(struct io_kiocb *req, unsigned int issue_flags)
 static struct io_async_msghdr *io_msg_alloc_async(struct io_kiocb *req)
 {
 	struct io_ring_ctx *ctx = req->ctx;
-	struct io_cache_entry *entry;
 	struct io_async_msghdr *hdr;
 
-	entry = io_alloc_cache_get(&ctx->netmsg_cache);
+	hdr = io_alloc_cache_get(&ctx->netmsg_cache);
-	if (entry) {
+	if (hdr) {
-		hdr = container_of(entry, struct io_async_msghdr, cache);
 		if (hdr->free_iov) {
 			kasan_mempool_unpoison_object(hdr->free_iov,
 				hdr->free_iov_nr * sizeof(struct iovec));
@@ -1490,11 +1488,10 @@ out:
 	return IOU_OK;
 }
 
-void io_netmsg_cache_free(struct io_cache_entry *entry)
+void io_netmsg_cache_free(const void *entry)
 {
-	struct io_async_msghdr *kmsg;
+	struct io_async_msghdr *kmsg = (struct io_async_msghdr *) entry;
 
-	kmsg = container_of(entry, struct io_async_msghdr, cache);
 	if (kmsg->free_iov) {
 		kasan_mempool_unpoison_object(kmsg->free_iov,
 				kmsg->free_iov_nr * sizeof(struct iovec));

io_uring/net.h

@@ -3,23 +3,15 @@
 #include <linux/net.h>
 #include <linux/uio.h>
 
-#include "alloc_cache.h"
-
 struct io_async_msghdr {
 #if defined(CONFIG_NET)
-	union {
+	struct iovec			fast_iov;
-		struct iovec			fast_iov;
-		struct {
-			struct io_cache_entry	cache;
-			/* entry size of ->free_iov, if valid */
-			int			free_iov_nr;
-		};
-	};
 	/* points to an allocated iov, if NULL we use fast_iov instead */
 	struct iovec			*free_iov;
+	int				free_iov_nr;
+	int				namelen;
 	__kernel_size_t			controllen;
 	__kernel_size_t			payloadlen;
-	int				namelen;
 	struct sockaddr __user		*uaddr;
 	struct msghdr			msg;
 	struct sockaddr_storage		addr;
@@ -57,9 +49,9 @@ int io_sendmsg_zc(struct io_kiocb *req, unsigned int issue_flags);
 int io_send_zc_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
 void io_send_zc_cleanup(struct io_kiocb *req);
 
-void io_netmsg_cache_free(struct io_cache_entry *entry);
+void io_netmsg_cache_free(const void *entry);
 #else
-static inline void io_netmsg_cache_free(struct io_cache_entry *entry)
+static inline void io_netmsg_cache_free(const void *entry)
 {
 }
 #endif

io_uring/poll.c

@@ -14,6 +14,7 @@
 #include <uapi/linux/io_uring.h>
 
 #include "io_uring.h"
+#include "alloc_cache.h"
 #include "refs.h"
 #include "napi.h"
 #include "opdef.h"
@@ -686,17 +687,15 @@ static struct async_poll *io_req_alloc_apoll(struct io_kiocb *req,
 					     unsigned issue_flags)
 {
 	struct io_ring_ctx *ctx = req->ctx;
-	struct io_cache_entry *entry;
 	struct async_poll *apoll;
 
 	if (req->flags & REQ_F_POLLED) {
 		apoll = req->apoll;
 		kfree(apoll->double_poll);
 	} else if (!(issue_flags & IO_URING_F_UNLOCKED)) {
-		entry = io_alloc_cache_get(&ctx->apoll_cache);
+		apoll = io_alloc_cache_get(&ctx->apoll_cache);
-		if (entry == NULL)
+		if (!apoll)
 			goto alloc_apoll;
-		apoll = container_of(entry, struct async_poll, cache);
 		apoll->poll.retries = APOLL_MAX_RETRY;
 	} else {
 alloc_apoll:
@@ -1055,8 +1054,3 @@ out:
 	io_req_set_res(req, ret, 0);
 	return IOU_OK;
 }
-
-void io_apoll_cache_free(struct io_cache_entry *entry)
-{
-	kfree(container_of(entry, struct async_poll, cache));
-}

io_uring/poll.h

@@ -1,7 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0
 
-#include "alloc_cache.h"
-
 enum {
 	IO_APOLL_OK,
 	IO_APOLL_ABORTED,
@@ -17,10 +15,7 @@ struct io_poll {
 };
 
 struct async_poll {
-	union {
+	struct io_poll		poll;
-		struct io_poll		poll;
-		struct io_cache_entry	cache;
-	};
 	struct io_poll		*double_poll;
 };
 
@@ -46,6 +41,4 @@ int io_arm_poll_handler(struct io_kiocb *req, unsigned issue_flags);
 bool io_poll_remove_all(struct io_ring_ctx *ctx, struct task_struct *tsk,
 			bool cancel_all);
 
-void io_apoll_cache_free(struct io_cache_entry *entry);
-
 void io_poll_task_func(struct io_kiocb *req, struct io_tw_state *ts);

io_uring/rsrc.c

@@ -13,6 +13,7 @@
 #include <uapi/linux/io_uring.h>
 
 #include "io_uring.h"
+#include "alloc_cache.h"
 #include "openclose.h"
 #include "rsrc.h"
 
@@ -169,7 +170,7 @@ static void io_rsrc_put_work(struct io_rsrc_node *node)
 
 void io_rsrc_node_destroy(struct io_ring_ctx *ctx, struct io_rsrc_node *node)
 {
-	if (!io_alloc_cache_put(&ctx->rsrc_node_cache, &node->cache))
+	if (!io_alloc_cache_put(&ctx->rsrc_node_cache, node))
 		kfree(node);
 }
 
@@ -197,12 +198,9 @@ void io_rsrc_node_ref_zero(struct io_rsrc_node *node)
 struct io_rsrc_node *io_rsrc_node_alloc(struct io_ring_ctx *ctx)
 {
 	struct io_rsrc_node *ref_node;
-	struct io_cache_entry *entry;
 
-	entry = io_alloc_cache_get(&ctx->rsrc_node_cache);
+	ref_node = io_alloc_cache_get(&ctx->rsrc_node_cache);
-	if (entry) {
+	if (!ref_node) {
-		ref_node = container_of(entry, struct io_rsrc_node, cache);
-	} else {
 		ref_node = kzalloc(sizeof(*ref_node), GFP_KERNEL);
 		if (!ref_node)
 			return NULL;

io_uring/rsrc.h

@@ -2,8 +2,6 @@
 #ifndef IOU_RSRC_H
 #define IOU_RSRC_H
 
-#include "alloc_cache.h"
-
 #define IO_NODE_ALLOC_CACHE_MAX 32
 
 #define IO_RSRC_TAG_TABLE_SHIFT	(PAGE_SHIFT - 3)
@@ -36,10 +34,7 @@ struct io_rsrc_data {
 };
 
 struct io_rsrc_node {
-	union {
+	struct io_ring_ctx		*ctx;
-		struct io_cache_entry		cache;
-		struct io_ring_ctx		*ctx;
-	};
 	int				refs;
 	bool				empty;
 	u16				type;

io_uring/rw.c

@@ -18,6 +18,7 @@
 #include "io_uring.h"
 #include "opdef.h"
 #include "kbuf.h"
+#include "alloc_cache.h"
 #include "rsrc.h"
 #include "poll.h"
 #include "rw.h"
@@ -154,7 +155,7 @@ static void io_rw_recycle(struct io_kiocb *req, unsigned int issue_flags)
 		return;
 	}
 	iov = rw->free_iovec;
-	if (io_alloc_cache_put(&req->ctx->rw_cache, &rw->cache)) {
+	if (io_alloc_cache_put(&req->ctx->rw_cache, rw)) {
 		if (iov)
 			kasan_mempool_poison_object(iov);
 		req->async_data = NULL;
@@ -200,12 +201,10 @@ static void io_req_rw_cleanup(struct io_kiocb *req, unsigned int issue_flags)
 static int io_rw_alloc_async(struct io_kiocb *req)
 {
 	struct io_ring_ctx *ctx = req->ctx;
-	struct io_cache_entry *entry;
 	struct io_async_rw *rw;
 
-	entry = io_alloc_cache_get(&ctx->rw_cache);
+	rw = io_alloc_cache_get(&ctx->rw_cache);
-	if (entry) {
+	if (rw) {
-		rw = container_of(entry, struct io_async_rw, cache);
 		if (rw->free_iovec) {
 			kasan_mempool_unpoison_object(rw->free_iovec,
 				rw->free_iov_nr * sizeof(struct iovec));
@@ -1168,11 +1167,10 @@ int io_do_iopoll(struct io_ring_ctx *ctx, bool force_nonspin)
 	return nr_events;
 }
 
-void io_rw_cache_free(struct io_cache_entry *entry)
+void io_rw_cache_free(const void *entry)
 {
-	struct io_async_rw *rw;
+	struct io_async_rw *rw = (struct io_async_rw *) entry;
 
-	rw = container_of(entry, struct io_async_rw, cache);
 	if (rw->free_iovec) {
 		kasan_mempool_unpoison_object(rw->free_iovec,
 				rw->free_iov_nr * sizeof(struct iovec));

io_uring/rw.h

@@ -3,10 +3,7 @@
 #include <linux/pagemap.h>
 
 struct io_async_rw {
-	union {
+	size_t				bytes_done;
-		size_t			bytes_done;
-		struct io_cache_entry	cache;
-	};
 	struct iov_iter			iter;
 	struct iov_iter_state		iter_state;
 	struct iovec			fast_iov;
@@ -28,4 +25,4 @@ void io_rw_fail(struct io_kiocb *req);
 void io_req_rw_complete(struct io_kiocb *req, struct io_tw_state *ts);
 int io_read_mshot_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
 int io_read_mshot(struct io_kiocb *req, unsigned int issue_flags);
-void io_rw_cache_free(struct io_cache_entry *entry);
+void io_rw_cache_free(const void *entry);

io_uring/uring_cmd.c

@@ -11,18 +11,17 @@
 #include <asm/ioctls.h>
 
 #include "io_uring.h"
+#include "alloc_cache.h"
 #include "rsrc.h"
 #include "uring_cmd.h"
 
 static struct uring_cache *io_uring_async_get(struct io_kiocb *req)
 {
 	struct io_ring_ctx *ctx = req->ctx;
-	struct io_cache_entry *entry;
 	struct uring_cache *cache;
 
-	entry = io_alloc_cache_get(&ctx->uring_cache);
+	cache = io_alloc_cache_get(&ctx->uring_cache);
-	if (entry) {
+	if (cache) {
-		cache = container_of(entry, struct uring_cache, cache);
 		req->flags |= REQ_F_ASYNC_DATA;
 		req->async_data = cache;
 		return cache;
@@ -39,7 +38,7 @@ static void io_req_uring_cleanup(struct io_kiocb *req, unsigned int issue_flags)
 
 	if (issue_flags & IO_URING_F_UNLOCKED)
 		return;
-	if (io_alloc_cache_put(&req->ctx->uring_cache, &cache->cache)) {
+	if (io_alloc_cache_put(&req->ctx->uring_cache, cache)) {
 		ioucmd->sqe = NULL;
 		req->async_data = NULL;
 		req->flags &= ~REQ_F_ASYNC_DATA;
@@ -354,8 +353,3 @@ int io_uring_cmd_sock(struct io_uring_cmd *cmd, unsigned int issue_flags)
 }
 EXPORT_SYMBOL_GPL(io_uring_cmd_sock);
 #endif
-
-void io_uring_cache_free(struct io_cache_entry *entry)
-{
-	kfree(container_of(entry, struct uring_cache, cache));
-}

io_uring/uring_cmd.h

@@ -1,15 +1,11 @@
 // SPDX-License-Identifier: GPL-2.0
 
 struct uring_cache {
-	union {
+	struct io_uring_sqe sqes[2];
-		struct io_cache_entry cache;
-		struct io_uring_sqe sqes[2];
-	};
 };
 
 int io_uring_cmd(struct io_kiocb *req, unsigned int issue_flags);
 int io_uring_cmd_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
-void io_uring_cache_free(struct io_cache_entry *entry);
 
 bool io_uring_try_cancel_uring_cmd(struct io_ring_ctx *ctx,
 				   struct task_struct *task, bool cancel_all);