linux-kernel - Re: [PATCH 2/3] tracing/user_events: Ensure bit is cleared on unregister

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Message-ID: <20230425135615.5801d0cf@gandalf.local.home>
Date:   Tue, 25 Apr 2023 13:56:15 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Beau Belgrave <beaub@...ux.microsoft.com>
Cc:     mhiramat@...nel.org, mathieu.desnoyers@...icios.com,
        dcook@...ux.microsoft.com, alanau@...ux.microsoft.com,
        linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] tracing/user_events: Ensure bit is cleared on
 unregister

On Tue, 25 Apr 2023 10:06:54 -0700
Beau Belgrave <beaub@...ux.microsoft.com> wrote:

> That's a good point, user_event_mm_fault() is a wrapper around
> fixup_user_fault(). We retry if it works, so I guess if the user could
> somehow cause a fail on the write and succeed to page in repeatedly, it
> could keep the loop going for that time period. I cannot think of a way
> to achieve this forever, but that doesn't mean it couldn't happen.
> 
> I can certainly add an upper bound of retries (maybe 3 or so?) if you
> think it would be possible for this to occur. I think we need retries of
> some amount to handle spurious faults.

Even 10 is fine. With a comment saying, "This really shouldn't loop more
than a couple of times, but we want to make sure some mischievous user
doesn't take advantage of this looping".

-- Steve