linux-kernel - Re: [PATCH bpf-next 1/4] bpf: enable task local storage for tracing programs

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Date:   Tue, 12 Jan 2021 10:21:45 -0800
From:   Martin KaFai Lau <kafai@...com>
To:     Song Liu <songliubraving@...com>
CC:     bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "andrii@...nel.org" <andrii@...nel.org>,
        "john.fastabend@...il.com" <john.fastabend@...il.com>,
        "kpsingh@...omium.org" <kpsingh@...omium.org>,
        Kernel Team <Kernel-team@...com>,
        "haoluo@...gle.com" <haoluo@...gle.com>,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH bpf-next 1/4] bpf: enable task local storage for tracing
 programs

On Mon, Jan 11, 2021 at 03:41:26PM -0800, Song Liu wrote:
> 
> 
> > On Jan 11, 2021, at 10:56 AM, Martin Lau <kafai@...com> wrote:
> > 
> > On Fri, Jan 08, 2021 at 03:19:47PM -0800, Song Liu wrote:
> > 
> > [ ... ]
> > 
> >> diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c
> >> index dd5aedee99e73..9bd47ad2b26f1 100644
> >> --- a/kernel/bpf/bpf_local_storage.c
> >> +++ b/kernel/bpf/bpf_local_storage.c
> >> @@ -140,17 +140,18 @@ static void __bpf_selem_unlink_storage(struct bpf_local_storage_elem *selem)
> >> {
> >> 	struct bpf_local_storage *local_storage;
> >> 	bool free_local_storage = false;
> >> +	unsigned long flags;
> >> 
> >> 	if (unlikely(!selem_linked_to_storage(selem)))
> >> 		/* selem has already been unlinked from sk */
> >> 		return;
> >> 
> >> 	local_storage = rcu_dereference(selem->local_storage);
> >> -	raw_spin_lock_bh(&local_storage->lock);
> >> +	raw_spin_lock_irqsave(&local_storage->lock, flags);
> > It will be useful to have a few words in commit message on this change
> > for future reference purpose.
> > 
> > Please also remove the in_irq() check from bpf_sk_storage.c
> > to avoid confusion in the future.  It probably should
> > be in a separate patch.
> 
> Do you mean we allow bpf_sk_storage_get_tracing() and 
> bpf_sk_storage_delete_tracing() in irq context? Like
Right.

However, after another thought, may be lets skip that for now
till a use case comes up and a test can be written.