linux-kernel - Re: [for-next][PATCH 0/2] ring-buffer: Fixes for v6.12

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Message-ID: <20241015113439.2f8155ac@gandalf.local.home>
Date: Tue, 15 Oct 2024 11:34:39 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: linux-kernel@...r.kernel.org
Cc: Masami Hiramatsu <mhiramat@...nel.org>, Mark Rutland
 <mark.rutland@....com>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [for-next][PATCH 0/2] ring-buffer: Fixes for v6.12

On Tue, 15 Oct 2024 11:31:05 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> ring-buffer: Fixes for v6.12
> 
> - Fix ref counter of buffers assigned at boot up
> 
>   A tracing instance can be created from the kernel command line.
>   If it maps to memory, it is considered permanent and should not
>   be deleted, or bad things can happen. If it is not mapped to memory,
>   then the user is fine to delete it via rmdir from the instances
>   directory. But the ref counts assumed 0 was free to remove and
>   greater than zero was not. But this was not the case. When an
>   instance is created, it should have the reference of 1, and if
>   it should not be removed, it must be greater than 1. The boot up
>   code set normal instances with a ref count of 0, which could get
>   removed if something accessed it and then released it. And memory
>   mapped instances had a ref count of 1 which meant it could be deleted,
>   and bad things happen. Keep normal instances ref count as 1, and
>   set memory mapped instances ref count to 2.
> 
> - Protect sub buffer size (order) updates from other modifications
> 
>   When a ring buffer is changing the size of its sub-buffers, no other
>   operations should be performed on the ring buffer. That includes
>   reading it. But the locking only grabbed the buffer->mutex that
>   keeps some operations from touching the ring buffer. It also must
>   hold the cpu_buffer->reader_lock as well when updates happen as
>   other paths use that to do some operations on the ring buffer.

Oops, used the wrong script. This was supposed to be "for-linus" not "for-next".

Oh well.

-- Steve