linux-kernel - Re: [PATCH] srcu: Use suitable gfp_flags for the init_srcu_struct

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Message-ID: <2D296DB9-2F60-47B2-A48A-D490A291A0EB@nvidia.com>
Date: Sat, 13 Dec 2025 19:02:21 +0000
From: Joel Fernandes <joelagnelf@...dia.com>
To: Zqiang <qiang.zhang@...ux.dev>
CC: "paulmck@...nel.org" <paulmck@...nel.org>, "frederic@...nel.org"
	<frederic@...nel.org>, "neeraj.upadhyay@...nel.org"
	<neeraj.upadhyay@...nel.org>, "rcu@...r.kernel.org" <rcu@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"qiang.zhang@...ux.dev" <qiang.zhang@...ux.dev>
Subject: Re: [PATCH] srcu: Use suitable gfp_flags for the
 init_srcu_struct_nodes()



> On Dec 13, 2025, at 10:56 PM, Zqiang <qiang.zhang@...ux.dev> wrote:
> 
> In some kernels which is set convert_to_big to SRCU_SIZING_INIT,
> for use the init_srcu_struct*() to initialized srcu structure,
> the is_static parameters is always false, the memory allocation
> for srcu_sup structure's->node can use GFP_KERNEL flags.
> 
> Signed-off-by: Zqiang <qiang.zhang@...ux.dev>
> ---
> kernel/rcu/srcutree.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> index ea3f128de06f..e4571b569752 100644
> --- a/kernel/rcu/srcutree.c
> +++ b/kernel/rcu/srcutree.c
> @@ -262,7 +262,7 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static)
>    ssp->srcu_sup->srcu_gp_seq_needed_exp = SRCU_GP_SEQ_INITIAL_VAL;
>    ssp->srcu_sup->srcu_last_gp_end = ktime_get_mono_fast_ns();
>    if (READ_ONCE(ssp->srcu_sup->srcu_size_state) == SRCU_SIZE_SMALL && SRCU_SIZING_IS_INIT()) {
> -        if (!init_srcu_struct_nodes(ssp, GFP_ATOMIC))
> +        if (!init_srcu_struct_nodes(ssp, !is_static ? GFP_KERNEL : GFP_ATOMIC))

Nit: please avoid double negatives, becomes a bit harder to read:

Instead,
is_static ? GFP_ATOMIC : GFP_KERNEL

Is it also worthwhile adding a might_sleep() here for additional robustness?

Thanks.



>            goto err_free_sda;
>        WRITE_ONCE(ssp->srcu_sup->srcu_size_state, SRCU_SIZE_BIG);
>    }
> --
> 2.48.1
> 
>