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From: Beau Belgrave <beaub@linux.microsoft.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-trace-kernel@vger.kernel.org,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>, bpf <bpf@vger.kernel.org>,
	David Vernet <void@manifault.com>,
	dthaler@microsoft.com, brauner@kernel.org, hch@infradead.org
Subject: Re: [PATCH] tracing/user_events: Run BPF program if attached
Date: Wed, 17 May 2023 16:00:54 -0700	[thread overview]
Message-ID: <20230517230054.GA195@W11-BEAU-MD.localdomain> (raw)
In-Reply-To: <CAHk-=wiiBfT4zNS29jA0XEsy8EmbqTH1hAPdRJCDAJMD8Gxt5A@mail.gmail.com>

On Wed, May 17, 2023 at 12:37:11PM -0700, Linus Torvalds wrote:
> On Wed, May 17, 2023 at 12:36 PM Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > .. this is the patch that I think should go on top of it to fix the
> > misleading "safe" and the incorrect RCU walk.
> 
> Let's actually attach the patch too. Duh.
> 
>                Linus

>  kernel/trace/trace_events_user.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
> index b2aecbfbbd24..054e28cc5ad4 100644
> --- a/kernel/trace/trace_events_user.c
> +++ b/kernel/trace/trace_events_user.c
> @@ -439,7 +439,7 @@ static bool user_event_enabler_exists(struct user_event_mm *mm,
>  	struct user_event_enabler *enabler;
>  	struct user_event_enabler *next;
>  
> -	list_for_each_entry_safe(enabler, next, &mm->enablers, link) {
> +	list_for_each_entry(enabler, next, &mm->enablers, link) {
>  		if (enabler->addr == uaddr &&
>  		    (enabler->values & ENABLE_VAL_BIT_MASK) == bit)
>  			return true;
> @@ -455,19 +455,19 @@ static void user_event_enabler_update(struct user_event *user)
>  	struct user_event_mm *next;
>  	int attempt;
>  
> +	lockdep_assert_held(&event_mutex);
> +
>  	while (mm) {
>  		next = mm->next;
>  		mmap_read_lock(mm->mm);
> -		rcu_read_lock();
>  
> -		list_for_each_entry_rcu(enabler, &mm->enablers, link) {
> +		list_for_each_entry(enabler, &mm->enablers, link) {
>  			if (enabler->event == user) {
>  				attempt = 0;
>  				user_event_enabler_write(mm, enabler, true, &attempt);
>  			}
>  		}
>  
> -		rcu_read_unlock();
>  		mmap_read_unlock(mm->mm);
>  		user_event_mm_put(mm);
>  		mm = next;

Do you mind giving me your Signed-off-by for these?

I plan to do a series where I take these patches and then also fix up a
few comments and the link namings as you suggested.

First patch is clean, second patch I made the following changes and
after that passed all the self-tests without bug splats with
CONFIG_PROVE_LOCKING/RCU and ATOMIC_SLEEP:

diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index b2aecbfbbd24..2f70dabb0f71 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -437,9 +437,8 @@ static bool user_event_enabler_exists(struct user_event_mm *mm,
                                      unsigned long uaddr, unsigned char bit)
 {
        struct user_event_enabler *enabler;
-       struct user_event_enabler *next;

-       list_for_each_entry_safe(enabler, next, &mm->enablers, link) {
+       list_for_each_entry(enabler, &mm->enablers, link) {
                if (enabler->addr == uaddr &&
                    (enabler->values & ENABLE_VAL_BIT_MASK) == bit)
                        return true;
@@ -495,7 +494,9 @@ static bool user_event_enabler_dup(struct user_event_enabler *orig,
        enabler->values = orig->values & ENABLE_VAL_DUP_MASK;

        refcount_inc(&enabler->event->refcnt);
-       list_add_rcu(&enabler->link, &mm->enablers);
+
+       /* Enablers not exposed yet, RCU not required */
+       list_add(&enabler->link, &mm->enablers);

  reply	other threads:[~2023-05-17 23:01 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-05-08 16:37 [PATCH] tracing/user_events: Run BPF program if attached Beau Belgrave
2023-05-09 15:24 ` Alexei Starovoitov
2023-05-09 17:01   ` Steven Rostedt
2023-05-09 20:30     ` Steven Rostedt
2023-05-09 20:42       ` Steven Rostedt
2023-05-15 16:57       ` Alexei Starovoitov
2023-05-15 18:33         ` Steven Rostedt
2023-05-15 19:35           ` Beau Belgrave
2023-05-15 21:38             ` Steven Rostedt
2023-05-15 19:24         ` Beau Belgrave
2023-05-15 21:57           ` Steven Rostedt
2023-05-17  0:36           ` Alexei Starovoitov
2023-05-17  0:56             ` Linus Torvalds
2023-05-17  1:46               ` Linus Torvalds
2023-05-17  2:29                 ` Steven Rostedt
2023-05-17  3:03                   ` Linus Torvalds
2023-05-17 17:22                     ` Beau Belgrave
2023-05-17 18:15                       ` Linus Torvalds
2023-05-17 19:07                         ` Beau Belgrave
2023-05-17 19:26                           ` Linus Torvalds
2023-05-17 19:36                             ` Beau Belgrave
2023-05-17 19:36                             ` Linus Torvalds
2023-05-17 19:37                               ` Linus Torvalds
2023-05-17 23:00                                 ` Beau Belgrave [this message]
2023-05-17 23:14                                   ` Linus Torvalds
2023-05-17 23:25                                     ` Steven Rostedt
2023-05-18  0:14                                       ` Beau Belgrave
2023-05-18  0:23                                         ` Linus Torvalds
2023-05-17 20:08                               ` Linus Torvalds
2023-05-17  1:26             ` Steven Rostedt
2023-05-17 16:50               ` Beau Belgrave
2023-05-18  0:10                 ` Alexei Starovoitov
2023-05-18  0:19                   ` Beau Belgrave
2023-05-18  0:56                     ` Alexei Starovoitov
2023-05-18  1:18                       ` Beau Belgrave
2023-05-18  2:08                         ` Steven Rostedt
2023-05-18  3:14                           ` Alexei Starovoitov
2023-05-18 13:36                             ` Steven Rostedt
2023-05-18 17:28                               ` Beau Belgrave
2023-06-01  9:46                   ` Christian Brauner
2023-06-01 15:24                     ` Beau Belgrave
2023-06-01 15:57                       ` Christian Brauner
2023-06-01 16:29                         ` Beau Belgrave
2023-06-06 13:37                           ` Masami Hiramatsu
2023-06-06 17:05                             ` Beau Belgrave
2023-06-07 14:07                               ` Masami Hiramatsu
2023-06-07 19:26                                 ` Beau Belgrave
2023-06-08  0:25                                   ` Masami Hiramatsu
2023-05-17 17:51             ` Beau Belgrave
2023-06-06 13:57             ` Masami Hiramatsu
2023-06-06 16:57               ` Andrii Nakryiko
2023-06-06 20:57                 ` Beau Belgrave

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