linux-kernel - Re: [PATCHv2 bpf-next 5/8] ftrace: Add update_ftrace_direct

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Message-ID: <CAADnVQKnnZkODUUDDJQNJ7tVnoGreggw5NuvaP81=rpUYXwd7g@mail.gmail.com>
Date: Thu, 13 Nov 2025 09:57:05 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Jiri Olsa <olsajiri@...il.com>
Cc: bot+bpf-ci@...nel.org, rostedt@...nel.org, 
	Florent Revest <revest@...gle.com>, Mark Rutland <mark.rutland@....com>, bpf <bpf@...r.kernel.org>, 
	LKML <linux-kernel@...r.kernel.org>, 
	linux-trace-kernel <linux-trace-kernel@...r.kernel.org>, 
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, 
	Menglong Dong <menglong8.dong@...il.com>, Song Liu <song@...nel.org>, 
	Martin KaFai Lau <martin.lau@...nel.org>, Eduard <eddyz87@...il.com>, 
	Yonghong Song <yonghong.song@...ux.dev>, Chris Mason <clm@...a.com>, 
	Ihor Solodrai <ihor.solodrai@...ux.dev>
Subject: Re: [PATCHv2 bpf-next 5/8] ftrace: Add update_ftrace_direct_mod function

On Thu, Nov 13, 2025 at 8:00 AM Jiri Olsa <olsajiri@...il.com> wrote:
>
> On Thu, Nov 13, 2025 at 01:02:17PM +0000, bot+bpf-ci@...nel.org wrote:
> > > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> > > index 433c36c3a..bacb6d9ab 100644
> > > --- a/include/linux/ftrace.h
> > > +++ b/include/linux/ftrace.h
> > > @@ -544,6 +544,7 @@ int modify_ftrace_direct_nolock(struct ftrace_ops *ops, unsigned long addr);
> > >
> > >  int update_ftrace_direct_add(struct ftrace_ops *ops, struct ftrace_hash *hash);
> > >  int update_ftrace_direct_del(struct ftrace_ops *ops, struct ftrace_hash *hash);
> > > +int update_ftrace_direct_mod(struct ftrace_ops *ops, struct ftrace_hash *hash, bool do_direct_lock);
> > >
> > >  void ftrace_stub_direct_tramp(void);
> > >
> > > @@ -581,6 +582,11 @@ int update_ftrace_direct_del(struct ftrace_ops *ops, struct ftrace_hash *hash)
> > >     return -ENODEV;
> > >  }
> > >
> > > +int modify_ftrace_direct_hash(struct ftrace_ops *ops, struct ftrace_hash *hash, bool do_direct_lock)
> >                 ^^^^^^^^^^^^^^^^^^^^^^^^^^
> > The stub function name doesn't match the declaration. Should this be
> > update_ftrace_direct_mod() instead of modify_ftrace_direct_hash()?
>
> it should, my bad
>
> >
> > > +{
> > > +   return -ENODEV;
> > > +}
> > > +
> >
> > [ ... ]
> >
> > > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> > > index 345f3fdd2..627d05b57 100644
> > > --- a/kernel/trace/ftrace.c
> > > +++ b/kernel/trace/ftrace.c
> > > @@ -6445,6 +6445,74 @@ int update_ftrace_direct_del(struct ftrace_ops *ops, struct ftrace_hash *hash)
> > >     return err;
> > >  }
> > >
> > > +int update_ftrace_direct_mod(struct ftrace_ops *ops, struct ftrace_hash *hash, bool do_direct_lock)
> > > +{
> > > +   struct ftrace_hash *orig_hash = ops->func_hash->filter_hash;
> > > +   struct ftrace_func_entry *entry, *tmp;
> > > +   static struct ftrace_ops tmp_ops = {
> > > +           .func           = ftrace_stub,
> > > +           .flags          = FTRACE_OPS_FL_STUB,
> > > +   };
> > > +   unsigned long size, i;
> > > +   int err;
> > > +
> > > +   if (!hash_count(hash))
> > > +           return 0;
> > > +   if (check_direct_multi(ops))
> > > +           return -EINVAL;
> > > +   if (!(ops->flags & FTRACE_OPS_FL_ENABLED))
> > > +           return -EINVAL;
> > > +   if (direct_functions == EMPTY_HASH)
> > > +           return -EINVAL;
> > > +
> > > +   if (do_direct_lock)
> > > +           mutex_lock(&direct_mutex);
> > > +
> > > +   /* Enable the tmp_ops to have the same functions as the direct ops */
> > > +   ftrace_ops_init(&tmp_ops);
> > > +   tmp_ops.func_hash = ops->func_hash;
> > > +
> > > +   err = register_ftrace_function_nolock(&tmp_ops);
> > > +   if (err)
> > > +           goto unlock;
> > > +
> > > +   /*
> > > +    * Call __ftrace_hash_update_ipmodify() here, so that we can call
> > > +    * ops->ops_func for the ops. This is needed because the above
> > > +    * register_ftrace_function_nolock() worked on tmp_ops.
> > > +    */
> > > +   err = __ftrace_hash_update_ipmodify(ops, orig_hash, orig_hash, true);
> >                                                                         ^^^^
> > Does __ftrace_hash_update_ipmodify() accept a fourth argument? The
> > function signature shows it only takes three parameters (ops, old_hash,
> > new_hash). This looks like a compilation error.
>
> the whole patchset is based on bpf-next/master plus Song's livepatch
> fixes which change modify_ftrace_direct_hash function, it's mentioned
> in the cover letter

Ohh. Will send bpf PR to Linus today and merge into bpf-next afterwards.