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

[Gabriel Krisman Bertazi <krisman@suse.de>]

Jens Axboe <axboe@kernel.dk> writes:

> 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.
>
> @@ -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

Among mostly ugly choices, this is an improvement over the init_once
callback.  I'd just fold the above codeguard into the code:

  if (IS_DEFINED(CONFIG_KASAN) && kmsg->free_iov)

Other than that,

Reviewed-by: Gabriel Krisman Bertazi <krisman@suse.de>


>  	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,

-- 
Gabriel Krisman Bertazi