linux-kernel - Re: [BUG RESEND] [BISECTED]: selftest: ftracetest: memleak in vfs

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Date:   Tue, 4 Apr 2023 18:24:28 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     Mirsad Goran Todorovac <mirsad.todorovac@....unizg.hr>,
        LKML <linux-kernel@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org,
        Thorsten Leemhuis <regressions@...mhuis.info>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org
Subject: Re: [BUG RESEND] [BISECTED]: selftest: ftracetest: memleak in
 vfs_write()

On Tue, 4 Apr 2023 15:07:44 -0700
Eric Biggers <ebiggers@...nel.org> wrote:

> This looks like an issue with the tracing subsystem.  I appreciate that you've
> now added the tracing maintainers to Cc.  I don't think your bisection to commit
> 71946a25f357 ("Merge tag 'mmc-v6.2' ...") is correct; that looks unrelated.

No that is not the correct commit. I think I see the issue. The error log
of a tracing instance doesn't seem to be freed if the instance is removed.

I'm guessing this can cause the bug:

 # cd /sys/kernel/tracincg
 # mkdir instances/foo
 # echo 'p:nothing no_function_here' > instances/foo/dynamic_events
 # rmdir instances/foo

I haven't tried the above commands so there may be a syntax error, but I
bet that would cause the issue. Basically, you need to create an instance,
cause a syntax error in creating something (which will add to the error log
list that shows the error), and then delete the instance.

I don't see where it would clean up the error log in that case, and it
would get leaked.

I'll write up a patch to fix this today (after confirming that does indeed
cause a leak).

-- Steve