io_uring: get rid of alloc cache init_once handling

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>

1 files changed, 12 insertions, 8 deletions

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
 };