linux-kernel - Re: [PATCH v2 5/5] audit: do not use exclusive wait in audit

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Message-ID: <e9edf9db340cbf753fce43772abdef4e.paul@paul-moore.com>
Date:   Fri, 19 May 2023 16:54:41 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Eiichi Tsukata <eiichi.tsukata@...anix.com>, eparis@...hat.com,
        linux-kernel@...r.kernel.org, audit@...r.kernel.org
Subject: Re: [PATCH v2 5/5] audit: do not use exclusive wait in audit_receive()

On May 11, 2023 Eiichi Tsukata <eiichi.tsukata@...anix.com> wrote:
> 
> kauditd thread issues wake_up() before it goes to sleep. The wake_up()
> call wakes up only one process as waiter side uses exclusive wait.
> This can be problematic when there are multiple processes (one is in
> audit_receive() and others are in audit_log_start()) waiting on
> audit_backlog_wait queue.
> 
> For example, if there are two processes waiting:
> 
>   Process (A): in audit_receive()
>   Process (B): in audit_log_start()
> 
> And (A) is at the head of the wait queue. Then kauditd's wake_up() only
> wakes up (A) leaving (B) as it is even if @audit_queue is drained. As a
> result, (B) can be blocked for up to backlog_wait_time.
> 
> To prevent the issue, use non-exclusive wait in audit_receive() so that
> kauditd can wake up all waiters in audit_receive().
> 
> Fixes: 8f110f530635 ("audit: ensure userspace is penalized the same as the kernel when under pressure")
> Signed-off-by: Eiichi Tsukata <eiichi.tsukata@...anix.com>
> ---
>  kernel/audit.c | 17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)

This was also discussed in the last patchset.

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