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

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Message-ID: <811D4BC0-A080-47C5-84AA-24EDE1C4EF6F@nvidia.com>
Date: Sun, 14 Dec 2025 07:50:33 +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>
Subject: Re: [PATCH] srcu: Use suitable gfp_flags for the
 init_srcu_struct_nodes()



> On Dec 14, 2025, at 12:28 PM, Zqiang <qiang.zhang@...ux.dev> wrote:
> 
> 
>> 
>> 
>>> 
>>>> 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
> 
> Ok, will do that.
> 
>> 
>> Is it also worthwhile adding a might_sleep() here for additional robustness?
> 
> Would it be more appropriate to add might_sleep() before
> allocating ssp->srcu_sup ?

Actually this is probably not needed because the slab allocator already does that for sleepable allocations.

So feel free to ignore the suggestion.;-)

The one reason to do it might just be for documentation.

Thanks.