[PATCH 05/11] io_uring/rsrc: protect node refs with uring_lock

Pavel Begunkov
2023-03-30T14:54:58Z

Currently, for nodes we have an atomic counter and some cached
(non-atomic) refs protected by uring_lock. Let's put all ref
manipulations under uring_lock and get rid of the atomic part.
It's free as in all cases we care about we already hold the lock.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
io_uring/io_uring.c | 18 ++++++++++++------
io_uring/rsrc.c | 30 ++++--------------------------
io_uring/rsrc.h | 29 +++++------------------------
3 files changed, 21 insertions(+), 56 deletions(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 52a88da65f57..e55c48d91209 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -967,7 +967,7 @@ bool io_aux_cqe(struct io_ring_ctx *ctx, bool defer, u64 user_data, s32 res, u32
return true;
}

-static void __io_req_complete_post(struct io_kiocb *req)
+static void __io_req_complete_post(struct io_kiocb *req, unsigned issue_flags)
{
struct io_ring_ctx *ctx = req->ctx;
struct io_rsrc_node *rsrc_node = NULL;
@@ -1003,7 +1003,11 @@ static void __io_req_complete_post(struct io_kiocb *req)
}
io_cq_unlock_post(ctx);

- io_put_rsrc_node(rsrc_node);
+ if (rsrc_node) {
+ io_ring_submit_lock(ctx, issue_flags);
+ io_put_rsrc_node(rsrc_node);
+ io_ring_submit_unlock(ctx, issue_flags);
+ }
}

void io_req_complete_post(struct io_kiocb *req, unsigned issue_flags)
@@ -1013,12 +1017,12 @@ void io_req_complete_post(struct io_kiocb *req, unsigned issue_flags)
io_req_task_work_add(req);
} else if (!(issue_flags & IO_URING_F_UNLOCKED) ||
!(req->ctx->flags & IORING_SETUP_IOPOLL)) {
- __io_req_complete_post(req);
+ __io_req_complete_post(req, issue_flags);
} else {
struct io_ring_ctx *ctx = req->ctx;

mutex_lock(&ctx->uring_lock);
- __io_req_complete_post(req);
+ __io_req_complete_post(req, issue_flags & ~IO_URING_F_UNLOCKED);
mutex_unlock(&ctx->uring_lock);
}
}
@@ -1120,7 +1124,10 @@ __cold void io_free_req_tw(struct io_kiocb *req, struct io_tw_state *ts)
{
struct io_ring_ctx *ctx = req->ctx;

- io_put_rsrc_node(req->rsrc_node);
+ if (req->rsrc_node) {
+ io_tw_lock(ctx, ts);
+ io_put_rsrc_node(req->rsrc_node);
+ }
io_dismantle_req(req);
io_put_task_remote(req->task, 1);

@@ -2791,7 +2798,6 @@ static void io_req_caches_free(struct io_ring_ctx *ctx)
static __cold void io_ring_ctx_free(struct io_ring_ctx *ctx)
{
io_sq_thread_finish(ctx);
- io_rsrc_refs_drop(ctx);
/* __io_rsrc_put_work() may need uring_lock to progress, wait w/o it */
io_wait_rsrc_data(ctx->buf_data);
io_wait_rsrc_data(ctx->file_data);
diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index 1e7c960737fd..1237fc77c250 100644
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -27,23 +27,10 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, struct iovec *iov,
struct io_mapped_ubuf **pimu,
struct page **last_hpage);

-#define IO_RSRC_REF_BATCH 100
-
/* only define max */
#define IORING_MAX_FIXED_FILES (1U << 20)
#define IORING_MAX_REG_BUFFERS (1U << 14)

-void io_rsrc_refs_drop(struct io_ring_ctx *ctx)
- __must_hold(&ctx->uring_lock)
-{
- struct io_rsrc_node *node = ctx->rsrc_node;
-
- if (node && node->cached_refs) {
- io_rsrc_put_node(node, node->cached_refs);
- node->cached_refs = 0;
- }
-}
-
int __io_account_mem(struct user_struct *user, unsigned long nr_pages)
{
unsigned long page_limit, cur_pages, new_pages;
@@ -153,13 +140,6 @@ static void io_buffer_unmap(struct io_ring_ctx *ctx, struct io_mapped_ubuf **slo
*slot = NULL;
}

-void io_rsrc_refs_refill(struct io_ring_ctx *ctx, struct io_rsrc_node *node)
- __must_hold(&ctx->uring_lock)
-{
- node->cached_refs += IO_RSRC_REF_BATCH;
- refcount_add(IO_RSRC_REF_BATCH, &node->refs);
-}
-
static void __io_rsrc_put_work(struct io_rsrc_node *ref_node)
{
struct io_rsrc_data *rsrc_data = ref_node->rsrc_data;
@@ -225,7 +205,8 @@ void io_rsrc_node_destroy(struct io_rsrc_node *ref_node)
kfree(ref_node);
}

-__cold void io_rsrc_node_ref_zero(struct io_rsrc_node *node)
+void io_rsrc_node_ref_zero(struct io_rsrc_node *node)
+ __must_hold(&node->rsrc_data->ctx->uring_lock)
{
struct io_ring_ctx *ctx = node->rsrc_data->ctx;
unsigned long flags;
@@ -269,7 +250,7 @@ static struct io_rsrc_node *io_rsrc_node_alloc(void)
if (!ref_node)
return NULL;

- refcount_set(&ref_node->refs, 1);
+ ref_node->refs = 1;
INIT_LIST_HEAD(&ref_node->node);
INIT_LIST_HEAD(&ref_node->rsrc_list);
ref_node->done = false;
@@ -283,8 +264,6 @@ void io_rsrc_node_switch(struct io_ring_ctx *ctx,
WARN_ON_ONCE(!ctx->rsrc_backup_node);
WARN_ON_ONCE(data_to_kill && !ctx->rsrc_node);

- io_rsrc_refs_drop(ctx);
-
if (data_to_kill) {
struct io_rsrc_node *rsrc_node = ctx->rsrc_node;

@@ -295,14 +274,13 @@ void io_rsrc_node_switch(struct io_ring_ctx *ctx,

atomic_inc(&data_to_kill->refs);
/* put master ref */
- io_rsrc_put_node(rsrc_node, 1);
+ io_put_rsrc_node(rsrc_node);
ctx->rsrc_node = NULL;
}

if (!ctx->rsrc_node) {
ctx->rsrc_node = ctx->rsrc_backup_node;
ctx->rsrc_backup_node = NULL;
- ctx->rsrc_node->cached_refs = 0;
}
}

diff --git a/io_uring/rsrc.h b/io_uring/rsrc.h
index 8164777279ba..fd3bdd30a993 100644
--- a/io_uring/rsrc.h
+++ b/io_uring/rsrc.h
@@ -37,13 +37,12 @@ struct io_rsrc_data {
};

struct io_rsrc_node {
- refcount_t refs;
+ int refs;
struct list_head node;
struct list_head rsrc_list;
struct io_rsrc_data *rsrc_data;
struct llist_node llist;
bool done;
- int cached_refs;
};

struct io_mapped_ubuf {
@@ -57,10 +56,8 @@ struct io_mapped_ubuf {
void io_rsrc_put_tw(struct callback_head *cb);
void io_rsrc_node_ref_zero(struct io_rsrc_node *node);
void io_rsrc_put_work(struct work_struct *work);
-void io_rsrc_refs_refill(struct io_ring_ctx *ctx, struct io_rsrc_node *node);
void io_wait_rsrc_data(struct io_rsrc_data *data);
void io_rsrc_node_destroy(struct io_rsrc_node *ref_node);
-void io_rsrc_refs_drop(struct io_ring_ctx *ctx);
int io_rsrc_node_switch_start(struct io_ring_ctx *ctx);
int io_queue_rsrc_removal(struct io_rsrc_data *data, unsigned idx,
struct io_rsrc_node *node, void *rsrc);
@@ -109,38 +106,22 @@ int io_register_rsrc_update(struct io_ring_ctx *ctx, void __user *arg,
int io_register_rsrc(struct io_ring_ctx *ctx, void __user *arg,
unsigned int size, unsigned int type);

-static inline void io_rsrc_put_node(struct io_rsrc_node *node, int nr)
-{
- if (refcount_sub_and_test(nr, &node->refs))
- io_rsrc_node_ref_zero(node);
-}
-
static inline void io_put_rsrc_node(struct io_rsrc_node *node)
{
- if (node)
- io_rsrc_put_node(node, 1);
+ if (node && !--node->refs)
+ io_rsrc_node_ref_zero(node);
}

static inline void io_req_put_rsrc_locked(struct io_kiocb *req,
struct io_ring_ctx *ctx)
- __must_hold(&ctx->uring_lock)
{
- struct io_rsrc_node *node = req->rsrc_node;
-
- if (node) {
- if (node == ctx->rsrc_node)
- node->cached_refs++;
- else
- io_rsrc_put_node(node, 1);
- }
+ io_put_rsrc_node(req->rsrc_node);
}

static inline void io_charge_rsrc_node(struct io_ring_ctx *ctx,
struct io_rsrc_node *node)
{
- node->cached_refs--;
- if (unlikely(node->cached_refs < 0))
- io_rsrc_refs_refill(ctx, node);
+ node->refs++;
}

static inline void io_req_set_rsrc_node(struct io_kiocb *req,
--
2.39.1