Re: [PATCH net 1/2] net/rds: do not fail init when CONFIG_SYSCTL=n

[Joel Granados <joel.granados@kernel.org>]

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On Wed, Oct 21, 2026 at 12:58:36PM -0700, Allison Henderson wrote:
> With CONFIG_SYSCTL=n, register_net_sysctl() and register_net_sysctl_sz()
> are inline stubs that return NULL.  rds_sysctl_init(),
> rds_ib_sysctl_init() and rds_tcp_init_net() all treat that NULL as
> -ENOMEM, so RDS refuses to initialize at all even though every tunable
> has a sane compiled-in default.
> 
> When RDS is built in, that is worse than a missing feature: the failed
> rds_init() destroys rds_wq, but the rds_rdma initcall still runs, and
> when rds_ib_sysctl_init() fails the same way, the error path in
> rds_ib_init() flushes the already freed workqueue:
> 
>   BUG: KASAN: slab-use-after-free in touch_wq_lockdep_map
>   ...
>    __flush_workqueue
>    rds_ib_init
>    rds_rdma_init
>   ...
>   Allocated by task 1:
>    alloc_workqueue_noprof
>    rds_threads_init
>    rds_init
>   ...
>   Freed by task 0:
>    kfree
>    rcu_do_batch
> 
> Only treat the NULL return as a failure when sysctl support is actually
> compiled in.  The exit paths need no change: unregister_net_sysctl_table()
> is an empty stub with CONFIG_SYSCTL=n and already tolerates a NULL header
> otherwise.
> 
> The underlying problem of built-in transports initializing after
> rds_init() has failed is independent of sysctl and is addressed
> separately.
> 
> Reported-by: kernel test robot <yi1.lai@intel.com>
> Closes: https://lore.kernel.org/oe-lkp/202610190310.9737b2e3-lkp@intel.com
> Fixes: 3e5048495c85 ("RDS: sysctls")
> Fixes: e6babe4cc4ce ("RDS/IB: Stats and sysctls")
> Fixes: c6a58ffed536 ("RDS: TCP: Add sysctl tunables for sndbuf/rcvbuf on rds-tcp socket")
> Suggested-by: Joel Granados <joel.granados@kernel.org>
> Assisted-by: LLM
> Signed-off-by: Allison Henderson <achender@kernel.org>
> ---
>  net/rds/ib_sysctl.c | 2 +-
>  net/rds/sysctl.c    | 2 +-
>  net/rds/tcp.c       | 2 +-
>  3 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/net/rds/ib_sysctl.c b/net/rds/ib_sysctl.c
> index 2af678e71e3c..bc97a3eecad6 100644
> --- a/net/rds/ib_sysctl.c
> +++ b/net/rds/ib_sysctl.c
> @@ -114,7 +114,7 @@ void rds_ib_sysctl_exit(void)
>  int rds_ib_sysctl_init(void)
>  {
>  	rds_ib_sysctl_hdr = register_net_sysctl(&init_net, "net/rds/ib", rds_ib_sysctl_table);
> -	if (!rds_ib_sysctl_hdr)
> +	if (!rds_ib_sysctl_hdr && IS_ENABLED(CONFIG_SYSCTL))
>  		return -ENOMEM;
>  	return 0;
>  }
> diff --git a/net/rds/sysctl.c b/net/rds/sysctl.c
> index 025f518a4349..968d6279bbd3 100644
> --- a/net/rds/sysctl.c
> +++ b/net/rds/sysctl.c
> @@ -103,7 +103,7 @@ int rds_sysctl_init(void)
>  
>  	rds_sysctl_reg_table =
>  		register_net_sysctl(&init_net, "net/rds", rds_sysctl_rds_table);
> -	if (!rds_sysctl_reg_table)
> +	if (!rds_sysctl_reg_table && IS_ENABLED(CONFIG_SYSCTL))
>  		return -ENOMEM;
>  	return 0;
>  }
> diff --git a/net/rds/tcp.c b/net/rds/tcp.c
> index 774a71f88d37..34815b4f658b 100644
> --- a/net/rds/tcp.c
> +++ b/net/rds/tcp.c
> @@ -637,7 +637,7 @@ static __net_init int rds_tcp_init_net(struct net *net)
>  	tbl[RDS_TCP_RCVBUF].data = &rtn->rcvbuf_size;
>  	rtn->rds_tcp_sysctl = register_net_sysctl_sz(net, "net/rds/tcp", tbl,
>  						     ARRAY_SIZE(rds_tcp_sysctl_table));
> -	if (!rtn->rds_tcp_sysctl) {
> +	if (!rtn->rds_tcp_sysctl && IS_ENABLED(CONFIG_SYSCTL)) {
>  		pr_warn("could not register sysctl\n");
>  		err = -ENOMEM;
>  		goto fail;
> -- 
> 2.50.1
> 

This LGTM

Reviewed-by: Joel Granados <joel.granados@kernel.org>

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