On Fri, Apr 09, 2021 at 12:38:59AM +0200, Frederic Weisbecker wrote:
> Once srcu_init() is called, the SRCU core is free to queue delayed
> workqueues, which rely on timers. However init_timers() is called
> several steps after rcu_init(). Any call_srcu() in-between would finish
> its course inside a dangerously uninitialized timer core.
>
> Make sure we stay in early SRCU mode until everything is well settled.
>
> Signed-off-by: Frederic Weisbecker <frede...@kernel.org>
> Cc: Uladzislau Rezki <ure...@gmail.com>
> Cc: Boqun Feng <boqun.f...@gmail.com>
> Cc: Lai Jiangshan <jiangshan...@gmail.com>
> Cc: Neeraj Upadhyay <neer...@codeaurora.org>
> Cc: Josh Triplett <j...@joshtriplett.org>
> Cc: Joel Fernandes <j...@joelfernandes.org>
Good catches! Apparently not so many people are using SRCU that early
in boot, but good to get it working. I queued this patch and the
preceding one (1/5).
Thanx, Paul
> ---
> include/linux/srcu.h | 6 ++++++
> init/main.c | 2 ++
> kernel/rcu/rcu.h | 6 ------
> kernel/rcu/srcutree.c | 5 +++++
> kernel/rcu/tiny.c | 1 -
> kernel/rcu/tree.c | 1 -
> 6 files changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/srcu.h b/include/linux/srcu.h
> index a0895bbf71ce..e6011a9975af 100644
> --- a/include/linux/srcu.h
> +++ b/include/linux/srcu.h
> @@ -64,6 +64,12 @@ unsigned long get_state_synchronize_srcu(struct
> srcu_struct *ssp);
> unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp);
> bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long
> cookie);
>
> +#ifdef CONFIG_SRCU
> +void srcu_init(void);
> +#else /* #ifdef CONFIG_SRCU */
> +static inline void srcu_init(void) { }
> +#endif /* #else #ifdef CONFIG_SRCU */
> +
> #ifdef CONFIG_DEBUG_LOCK_ALLOC
>
> /**
> diff --git a/init/main.c b/init/main.c
> index 53b278845b88..1bc5cc9e52ef 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -42,6 +42,7 @@
> #include <linux/profile.h>
> #include <linux/kfence.h>
> #include <linux/rcupdate.h>
> +#include <linux/srcu.h>
> #include <linux/moduleparam.h>
> #include <linux/kallsyms.h>
> #include <linux/writeback.h>
> @@ -956,6 +957,7 @@ asmlinkage __visible void __init __no_sanitize_address
> start_kernel(void)
> tick_init();
> rcu_init_nohz();
> init_timers();
> + srcu_init();
> hrtimers_init();
> softirq_init();
> timekeeping_init();
> diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
> index d64b842f4078..b3af34068051 100644
> --- a/kernel/rcu/rcu.h
> +++ b/kernel/rcu/rcu.h
> @@ -422,12 +422,6 @@ do {
> \
>
> #endif /* #if defined(CONFIG_SRCU) || !defined(CONFIG_TINY_RCU) */
>
> -#ifdef CONFIG_SRCU
> -void srcu_init(void);
> -#else /* #ifdef CONFIG_SRCU */
> -static inline void srcu_init(void) { }
> -#endif /* #else #ifdef CONFIG_SRCU */
> -
> #ifdef CONFIG_TINY_RCU
> /* Tiny RCU doesn't expedite, as its purpose in life is instead to be tiny.
> */
> static inline bool rcu_gp_is_normal(void) { return true; }
> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> index 10e681ea7051..108f9ca06047 100644
> --- a/kernel/rcu/srcutree.c
> +++ b/kernel/rcu/srcutree.c
> @@ -1384,6 +1384,11 @@ void __init srcu_init(void)
> {
> struct srcu_struct *ssp;
>
> + /*
> + * Once that is set, call_srcu() can follow the normal path and
> + * queue delayed work. This must follow RCU workqueues creation
> + * and timers initialization.
> + */
> srcu_init_done = true;
> while (!list_empty(&srcu_boot_list)) {
> ssp = list_first_entry(&srcu_boot_list, struct srcu_struct,
> diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
> index c8a029fbb114..340b3f8b090d 100644
> --- a/kernel/rcu/tiny.c
> +++ b/kernel/rcu/tiny.c
> @@ -221,5 +221,4 @@ void __init rcu_init(void)
> {
> open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
> rcu_early_boot_tests();
> - srcu_init();
> }
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 5c214705c33f..740f5cd34459 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -4714,7 +4714,6 @@ void __init rcu_init(void)
> WARN_ON(!rcu_gp_wq);
> rcu_par_gp_wq = alloc_workqueue("rcu_par_gp", WQ_MEM_RECLAIM, 0);
> WARN_ON(!rcu_par_gp_wq);
> - srcu_init();
>
> /* Fill in default value for rcutree.qovld boot parameter. */
> /* -After- the rcu_node ->lock fields are initialized! */
> --
> 2.25.1
>
