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

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Message-ID: <e4030c94bbc55d1e78f0d26039561f583ff0cadf@linux.dev>
Date: Sun, 14 Dec 2025 03:27:44 +0000
From: "Zqiang" <qiang.zhang@...ux.dev>
To: "Joel Fernandes" <joelagnelf@...dia.com>
Cc: paulmck@...nel.org, frederic@...nel.org, neeraj.upadhyay@...nel.org,
 rcu@...r.kernel.org, linux-kernel@...r.kernel.org
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

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 ?

Thanks
Zqiang


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