From: Steven Rostedt <rostedt@goodmis.org>
To: Beau Belgrave <beaub@linux.microsoft.com>
Cc: mhiramat@kernel.org, linux-trace-devel@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v6 02/13] user_events: Add minimal support for trace_event into ftrace
Date: Thu, 9 Dec 2021 12:47:35 -0500 [thread overview]
Message-ID: <20211209124735.3d1a9707@gandalf.local.home> (raw)
In-Reply-To: <20211209174050.GA21553@kbox>
On Thu, 9 Dec 2021 09:40:50 -0800
Beau Belgrave <beaub@linux.microsoft.com> wrote:
> No, this is not a fast path, and I don't have a problem moving to a
> mutex if you feel that is better. I've likely become too close to this
> code to know when things are confusing for others.
Yeah. I really dislike the "protection by algorithms" then protection by
locking unless it is a fast path.
If this was a fast path then I'd be more concerned. I dislike global locks
as well, but unless contention becomes a concern, I don't think we should
worry about it.
Also, for this comment:
+static int user_events_release(struct inode *node, struct file *file)
+{
+ struct user_event_refs *refs;
+ struct user_event *user;
+ int i;
+
+ /*
+ * refs is protected by RCU and could in theory change immediately
+ * before this call on another core. To ensure we read the latest
+ * version of refs we acquire the RCU read lock again.
+ */
+ rcu_read_lock_sched();
+ refs = rcu_dereference_sched(file->private_data);
+ rcu_read_unlock_sched();
How do you see refs changing on another core if this can only be called
when nothing has a reference to it?
I think this comment and grabbing the rcu locks is what is causing me
concern.
-- Steve
next prev parent reply other threads:[~2021-12-09 17:47 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-01 18:25 [PATCH v6 00/13] user_events: Enable user processes to create and write to trace events Beau Belgrave
2021-12-01 18:25 ` [PATCH v6 01/13] user_events: Add UABI header for user access to user_events Beau Belgrave
2021-12-01 18:25 ` [PATCH v6 02/13] user_events: Add minimal support for trace_event into ftrace Beau Belgrave
2021-12-08 23:19 ` Steven Rostedt
2021-12-09 0:58 ` Beau Belgrave
2021-12-09 2:03 ` Steven Rostedt
2021-12-09 17:40 ` Beau Belgrave
2021-12-09 17:47 ` Steven Rostedt [this message]
2021-12-09 19:42 ` Beau Belgrave
2021-12-09 19:57 ` Steven Rostedt
2021-12-09 20:11 ` Beau Belgrave
2021-12-09 20:19 ` Steven Rostedt
2021-12-01 18:25 ` [PATCH v6 03/13] user_events: Add print_fmt generation support for basic types Beau Belgrave
2021-12-01 18:25 ` [PATCH v6 04/13] user_events: Handle matching arguments from dyn_events Beau Belgrave
2021-12-01 18:25 ` [PATCH v6 05/13] user_events: Add basic perf and eBPF support Beau Belgrave
2021-12-01 18:25 ` [PATCH v6 06/13] user_events: Add self-test for ftrace integration Beau Belgrave
2021-12-01 18:25 ` [PATCH v6 07/13] user_events: Add self-test for dynamic_events integration Beau Belgrave
2021-12-01 18:25 ` [PATCH v6 08/13] user_events: Add self-test for perf_event integration Beau Belgrave
2021-12-01 18:25 ` [PATCH v6 09/13] user_events: Optimize writing events by only copying data once Beau Belgrave
2021-12-01 18:25 ` [PATCH v6 10/13] user_events: Add documentation file Beau Belgrave
2021-12-01 18:25 ` [PATCH v6 11/13] user_events: Add sample code for typical usage Beau Belgrave
2021-12-01 18:25 ` [PATCH v6 12/13] user_events: Validate user payloads for size and null termination Beau Belgrave
2021-12-01 18:25 ` [PATCH v6 13/13] user_events: Use __get_rel_str for relative string fields Beau Belgrave
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20211209124735.3d1a9707@gandalf.local.home \
--to=rostedt@goodmis.org \
--cc=beaub@linux.microsoft.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-trace-devel@vger.kernel.org \
--cc=mhiramat@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).