linux-kernel - [PATCH v3 0/4] tracing/user_events: Use non-RCU context for enabler writes

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Message-Id: <20230519230741.669-1-beaub@linux.microsoft.com>
Date:   Fri, 19 May 2023 16:07:37 -0700
From:   Beau Belgrave <beaub@...ux.microsoft.com>
To:     rostedt@...dmis.org, mhiramat@...nel.org
Cc:     linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        torvalds@...ux-foundation.org, ast@...nel.org
Subject: [PATCH v3 0/4] tracing/user_events: Use non-RCU context for enabler writes

Currently when events are enabled/disabled a top level mm enumeration is
done in a non-RCU context, however, the enablers are still in a
RCU-context. Each enabler is updated via user_event_enabler_write() which
uses pin_user_pages_remote(). This function can reschedule and should not
be used from a RCU-context, which this series addresses.

There was also feedback given that some of the code was confusing and
needed further comments and field renames, especially for links. I think
having this feedback will help others contribute to this code easier, so
I am grouping this into a single series to address this together.

NOTE: Series is based on the for-next branch of the following tree:
git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git

Change history

V3:
Use Linus's patches to more completely solve this issue.

Added comments and renamed fields as suggested by Linus to ensure easier
reasoning over the code for everyone.

V2:
Remove break statement that prevents more than 1 enabler in MM for same
event (rare, but possible).

Beau Belgrave (2):
  tracing/user_events: Rename link fields for clarity
  tracing/user_events: Document user_event_mm one-shot list usage

Linus Torvalds (2):
  tracing/user_events: Split up mm alloc and attach
  tracing/user_events: Remove RCU lock while pinning pages

 include/linux/user_events.h      |  3 +-
 kernel/trace/trace_events_user.c | 97 +++++++++++++++++++++-----------
 2 files changed, 67 insertions(+), 33 deletions(-)

base-commit: 3862f86c1529fa0016de6344eb974877b4cd3838
-- 
2.25.1