[PATCH 2/3] io_uring: get rid of alloc cache init_once handling

Jens Axboe
2025-01-23T18:48:00Z

init_once is called when an object doesn't come from the cache, and
hence needs initial clearing of certain members. While the whole
struct could get cleared by memset() in that case, a few of the cache
members are large enough that this may cause unnecessary overhead if
the caches used aren't large enough to satisfy the workload. For those
cases, some churn of kmalloc+kfree is to be expected.

Ensure that the 3 users that need clearing put the members they need
cleared at the start of the struct, and wrap the rest of the struct in
a struct group so the offset is known.

While at it, improve the interaction with KASAN such that when/if
KASAN writes to members inside the struct that should be retained over
caching, it won't trip over itself. For rw and net, the retaining of
the iovec over caching is disabled if KASAN is enabled. A helper will
free and clear those members in that case.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
include/linux/io_uring/cmd.h | 2 +-
include/linux/io_uring_types.h | 3 ++-
io_uring/alloc_cache.h | 43 +++++++++++++++++++++++++++-------
io_uring/futex.c | 4 ++--
io_uring/io_uring.c | 12 ++++++----
io_uring/io_uring.h | 5 ++--
io_uring/net.c | 28 +++++-----------------
io_uring/net.h | 20 +++++++++-------
io_uring/poll.c | 2 +-
io_uring/rw.c | 27 +++++----------------
io_uring/rw.h | 27 ++++++++++++---------
io_uring/uring_cmd.c | 11 ++-------
12 files changed, 91 insertions(+), 93 deletions(-)

diff --git a/include/linux/io_uring/cmd.h b/include/linux/io_uring/cmd.h
index a3ce553413de..abd0c8bd950b 100644
--- a/include/linux/io_uring/cmd.h
+++ b/include/linux/io_uring/cmd.h
@@ -19,8 +19,8 @@ struct io_uring_cmd {
};

struct io_uring_cmd_data {
- struct io_uring_sqe sqes[2];
void *op_data;
+ struct io_uring_sqe sqes[2];
};

static inline const void *io_uring_sqe_cmd(const struct io_uring_sqe *sqe)
diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
index 623d8e798a11..3def525a1da3 100644
--- a/include/linux/io_uring_types.h
+++ b/include/linux/io_uring_types.h
@@ -222,7 +222,8 @@ struct io_alloc_cache {
void **entries;
unsigned int nr_cached;
unsigned int max_cached;
- size_t elem_size;
+ unsigned int elem_size;
+ unsigned int init_clear;
};

struct io_ring_ctx {
diff --git a/io_uring/alloc_cache.h b/io_uring/alloc_cache.h
index a3a8cfec32ce..cca96aff3277 100644
--- a/io_uring/alloc_cache.h
+++ b/io_uring/alloc_cache.h
@@ -6,6 +6,19 @@
*/
#define IO_ALLOC_CACHE_MAX 128

+#if defined(CONFIG_KASAN)
+static inline void io_alloc_cache_kasan(struct iovec **iov, int *nr)
+{
+ kfree(*iov);
+ *iov = NULL;
+ *nr = 0;
+}
+#else
+static inline void io_alloc_cache_kasan(struct iovec **iov, int *nr)
+{
+}
+#endif
+
static inline bool io_alloc_cache_put(struct io_alloc_cache *cache,
void *entry)
{
@@ -23,35 +36,47 @@ static inline void *io_alloc_cache_get(struct io_alloc_cache *cache)
if (cache->nr_cached) {
void *entry = cache->entries[--cache->nr_cached];

+ /*
+ * If KASAN is enabled, always clear the initial bytes that
+ * must be zeroed post alloc, in case any of them overlap
+ * with KASAN storage.
+ */
+#if defined(CONFIG_KASAN)
kasan_mempool_unpoison_object(entry, cache->elem_size);
+ if (cache->init_clear)
+ memset(entry, 0, cache->init_clear);
+#endif
return entry;
}

return NULL;
}

-static inline void *io_cache_alloc(struct io_alloc_cache *cache, gfp_t gfp,
- void (*init_once)(void *obj))
+static inline void *io_cache_alloc(struct io_alloc_cache *cache, gfp_t gfp)
{
- if (unlikely(!cache->nr_cached)) {
- void *obj = kmalloc(cache->elem_size, gfp);
+ void *obj;

- if (obj && init_once)
- init_once(obj);
+ obj = io_alloc_cache_get(cache);
+ if (obj)
return obj;
- }
- return io_alloc_cache_get(cache);
+
+ obj = kmalloc(cache->elem_size, gfp);
+ if (obj && cache->init_clear)
+ memset(obj, 0, cache->init_clear);
+ return obj;
}

/* 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)
+ unsigned max_nr, unsigned int size,
+ unsigned int init_bytes)
{
cache->entries = kvmalloc_array(max_nr, sizeof(void *), GFP_KERNEL);
if (cache->entries) {
cache->nr_cached = 0;
cache->max_cached = max_nr;
cache->elem_size = size;
+ cache->init_clear = init_bytes;
return false;
}
return true;
diff --git a/io_uring/futex.c b/io_uring/futex.c
index 30139cc150f2..3159a2b7eeca 100644
--- a/io_uring/futex.c
+++ b/io_uring/futex.c
@@ -36,7 +36,7 @@ struct io_futex_data {
bool io_futex_cache_init(struct io_ring_ctx *ctx)
{
return io_alloc_cache_init(&ctx->futex_cache, IO_FUTEX_ALLOC_CACHE_MAX,
- sizeof(struct io_futex_data));
+ sizeof(struct io_futex_data), 0);
}

void io_futex_cache_free(struct io_ring_ctx *ctx)
@@ -320,7 +320,7 @@ int io_futex_wait(struct io_kiocb *req, unsigned int issue_flags)
}

io_ring_submit_lock(ctx, issue_flags);
- ifd = io_cache_alloc(&ctx->futex_cache, GFP_NOWAIT, NULL);
+ ifd = io_cache_alloc(&ctx->futex_cache, GFP_NOWAIT);
if (!ifd) {
ret = -ENOMEM;
goto done_unlock;
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 7bfbc7c22367..263e504be4a8 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -315,16 +315,18 @@ 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);
ret = io_alloc_cache_init(&ctx->apoll_cache, IO_POLL_ALLOC_CACHE_MAX,
- sizeof(struct async_poll));
+ sizeof(struct async_poll), 0);
ret |= io_alloc_cache_init(&ctx->netmsg_cache, IO_ALLOC_CACHE_MAX,
- sizeof(struct io_async_msghdr));
+ sizeof(struct io_async_msghdr),
+ offsetof(struct io_async_msghdr, clear));
ret |= io_alloc_cache_init(&ctx->rw_cache, IO_ALLOC_CACHE_MAX,
- sizeof(struct io_async_rw));
+ sizeof(struct io_async_rw),
+ offsetof(struct io_async_rw, clear));
ret |= io_alloc_cache_init(&ctx->uring_cache, IO_ALLOC_CACHE_MAX,
- sizeof(struct io_uring_cmd_data));
+ sizeof(struct io_uring_cmd_data), 0);
spin_lock_init(&ctx->msg_lock);
ret |= io_alloc_cache_init(&ctx->msg_cache, IO_ALLOC_CACHE_MAX,
- sizeof(struct io_kiocb));
+ sizeof(struct io_kiocb), 0);
ret |= io_futex_cache_init(ctx);
if (ret)
goto free_ref;
diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
index f65e3f3ede51..67adbb3c1bf5 100644
--- a/io_uring/io_uring.h
+++ b/io_uring/io_uring.h
@@ -226,10 +226,9 @@ static inline void io_req_set_res(struct io_kiocb *req, s32 res, u32 cflags)
}

static inline void *io_uring_alloc_async_data(struct io_alloc_cache *cache,
- struct io_kiocb *req,
- void (*init_once)(void *obj))
+ struct io_kiocb *req)
{
- req->async_data = io_cache_alloc(cache, GFP_KERNEL, init_once);
+ req->async_data = io_cache_alloc(cache, GFP_KERNEL);
if (req->async_data)
req->flags |= REQ_F_ASYNC_DATA;
return req->async_data;
diff --git a/io_uring/net.c b/io_uring/net.c
index 85f55fbc25c9..41eef286f8b9 100644
--- a/io_uring/net.c
+++ b/io_uring/net.c
@@ -137,7 +137,6 @@ static void io_netmsg_iovec_free(struct io_async_msghdr *kmsg)
static void io_netmsg_recycle(struct io_kiocb *req, unsigned int issue_flags)
{
struct io_async_msghdr *hdr = req->async_data;
- struct iovec *iov;

/* can't recycle, ensure we free the iovec if we have one */
if (unlikely(issue_flags & IO_URING_F_UNLOCKED)) {
@@ -146,39 +145,25 @@ 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;
+ io_alloc_cache_kasan(&hdr->free_iov, &hdr->free_iov_nr);
if (io_alloc_cache_put(&req->ctx->netmsg_cache, hdr)) {
- if (iov)
- kasan_mempool_poison_object(iov);
req->async_data = NULL;
req->flags &= ~REQ_F_ASYNC_DATA;
}
}

-static void io_msg_async_data_init(void *obj)
-{
- struct io_async_msghdr *hdr = (struct io_async_msghdr *)obj;
-
- hdr->free_iov = NULL;
- hdr->free_iov_nr = 0;
-}
-
static struct io_async_msghdr *io_msg_alloc_async(struct io_kiocb *req)
{
struct io_ring_ctx *ctx = req->ctx;
struct io_async_msghdr *hdr;

- hdr = io_uring_alloc_async_data(&ctx->netmsg_cache, req,
- io_msg_async_data_init);
+ hdr = io_uring_alloc_async_data(&ctx->netmsg_cache, req);
if (!hdr)
return NULL;

/* If the async data was cached, we might have an iov cached inside. */
- if (hdr->free_iov) {
- kasan_mempool_unpoison_object(hdr->free_iov,
- hdr->free_iov_nr * sizeof(struct iovec));
+ if (hdr->free_iov)
req->flags |= REQ_F_NEED_CLEANUP;
- }
return hdr;
}

@@ -1813,11 +1798,10 @@ void io_netmsg_cache_free(const void *entry)
{
struct io_async_msghdr *kmsg = (struct io_async_msghdr *) entry;

- if (kmsg->free_iov) {
- kasan_mempool_unpoison_object(kmsg->free_iov,
- kmsg->free_iov_nr * sizeof(struct iovec));
+#if !defined(CONFIG_KASAN)
+ if (kmsg->free_iov)
io_netmsg_iovec_free(kmsg);
- }
+#endif
kfree(kmsg);
}
#endif
diff --git a/io_uring/net.h b/io_uring/net.h
index 52bfee05f06a..b804c2b36e60 100644
--- a/io_uring/net.h
+++ b/io_uring/net.h
@@ -5,16 +5,20 @@

struct io_async_msghdr {
#if defined(CONFIG_NET)
- struct iovec fast_iov;
- /* points to an allocated iov, if NULL we use fast_iov instead */
struct iovec *free_iov;
+ /* points to an allocated iov, if NULL we use fast_iov instead */
int free_iov_nr;
- int namelen;
- __kernel_size_t controllen;
- __kernel_size_t payloadlen;
- struct sockaddr __user *uaddr;
- struct msghdr msg;
- struct sockaddr_storage addr;
+ struct_group(clear,
+ int namelen;
+ struct iovec fast_iov;
+ __kernel_size_t controllen;
+ __kernel_size_t payloadlen;
+ struct sockaddr __user *uaddr;
+ struct msghdr msg;
+ struct sockaddr_storage addr;
+ );
+#else
+ struct_group(clear);
#endif
};

diff --git a/io_uring/poll.c b/io_uring/poll.c
index cc01c40b43d3..356474c66f32 100644
--- a/io_uring/poll.c
+++ b/io_uring/poll.c
@@ -650,7 +650,7 @@ static struct async_poll *io_req_alloc_apoll(struct io_kiocb *req,
kfree(apoll->double_poll);
} else {
if (!(issue_flags & IO_URING_F_UNLOCKED))
- apoll = io_cache_alloc(&ctx->apoll_cache, GFP_ATOMIC, NULL);
+ apoll = io_cache_alloc(&ctx->apoll_cache, GFP_ATOMIC);
else
apoll = kmalloc(sizeof(*apoll), GFP_ATOMIC);
if (!apoll)
diff --git a/io_uring/rw.c b/io_uring/rw.c
index a9a2733be842..991ecfbea88e 100644
--- a/io_uring/rw.c
+++ b/io_uring/rw.c
@@ -158,16 +158,13 @@ static void io_rw_iovec_free(struct io_async_rw *rw)
static void io_rw_recycle(struct io_kiocb *req, unsigned int issue_flags)
{
struct io_async_rw *rw = req->async_data;
- struct iovec *iov;

if (unlikely(issue_flags & IO_URING_F_UNLOCKED)) {
io_rw_iovec_free(rw);
return;
}
- iov = rw->free_iovec;
+ io_alloc_cache_kasan(&rw->free_iovec, &rw->free_iov_nr);
if (io_alloc_cache_put(&req->ctx->rw_cache, rw)) {
- if (iov)
- kasan_mempool_poison_object(iov);
req->async_data = NULL;
req->flags &= ~REQ_F_ASYNC_DATA;
}
@@ -208,27 +205,16 @@ static void io_req_rw_cleanup(struct io_kiocb *req, unsigned int issue_flags)
}
}

-static void io_rw_async_data_init(void *obj)
-{
- struct io_async_rw *rw = (struct io_async_rw *)obj;
-
- rw->free_iovec = NULL;
- rw->bytes_done = 0;
-}
-
static int io_rw_alloc_async(struct io_kiocb *req)
{
struct io_ring_ctx *ctx = req->ctx;
struct io_async_rw *rw;

- rw = io_uring_alloc_async_data(&ctx->rw_cache, req, io_rw_async_data_init);
+ rw = io_uring_alloc_async_data(&ctx->rw_cache, req);
if (!rw)
return -ENOMEM;
- if (rw->free_iovec) {
- kasan_mempool_unpoison_object(rw->free_iovec,
- rw->free_iov_nr * sizeof(struct iovec));
+ if (rw->free_iovec)
req->flags |= REQ_F_NEED_CLEANUP;
- }
rw->bytes_done = 0;
return 0;
}
@@ -1323,10 +1309,9 @@ void io_rw_cache_free(const void *entry)
{
struct io_async_rw *rw = (struct io_async_rw *) entry;

- if (rw->free_iovec) {
- kasan_mempool_unpoison_object(rw->free_iovec,
- rw->free_iov_nr * sizeof(struct iovec));
+#if !defined(CONFIG_KASAN)
+ if (rw->free_iovec)
io_rw_iovec_free(rw);
- }
+#endif
kfree(rw);
}
diff --git a/io_uring/rw.h b/io_uring/rw.h
index 2d7656bd268d..eaa59bd64870 100644
--- a/io_uring/rw.h
+++ b/io_uring/rw.h
@@ -9,19 +9,24 @@ struct io_meta_state {

struct io_async_rw {
size_t bytes_done;
- struct iov_iter iter;
- struct iov_iter_state iter_state;
- struct iovec fast_iov;
struct iovec *free_iovec;
- int free_iov_nr;
- /* wpq is for buffered io, while meta fields are used with direct io */
- union {
- struct wait_page_queue wpq;
- struct {
- struct uio_meta meta;
- struct io_meta_state meta_state;
+ struct_group(clear,
+ struct iov_iter iter;
+ struct iov_iter_state iter_state;
+ struct iovec fast_iov;
+ int free_iov_nr;
+ /*
+ * wpq is for buffered io, while meta fields are used with
+ * direct io
+ */
+ union {
+ struct wait_page_queue wpq;
+ struct {
+ struct uio_meta meta;
+ struct io_meta_state meta_state;
+ };
};
- };
+ );
};

int io_prep_read_fixed(struct io_kiocb *req, const struct io_uring_sqe *sqe);
diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
index 6a63ec4b5445..1f6a82128b47 100644
--- a/io_uring/uring_cmd.c
+++ b/io_uring/uring_cmd.c
@@ -168,23 +168,16 @@ void io_uring_cmd_done(struct io_uring_cmd *ioucmd, ssize_t ret, u64 res2,
}
EXPORT_SYMBOL_GPL(io_uring_cmd_done);

-static void io_uring_cmd_init_once(void *obj)
-{
- struct io_uring_cmd_data *data = obj;
-
- data->op_data = NULL;
-}
-
static int io_uring_cmd_prep_setup(struct io_kiocb *req,
const struct io_uring_sqe *sqe)
{
struct io_uring_cmd *ioucmd = io_kiocb_to_cmd(req, struct io_uring_cmd);
struct io_uring_cmd_data *cache;

- cache = io_uring_alloc_async_data(&req->ctx->uring_cache, req,
- io_uring_cmd_init_once);
+ cache = io_uring_alloc_async_data(&req->ctx->uring_cache, req);
if (!cache)
return -ENOMEM;
+ cache->op_data = NULL;

if (!(req->flags & REQ_F_FORCE_ASYNC)) {
/* defer memcpy until we need it */
--
2.47.2