On Tue, Feb 20, 2018 at 9:06 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> On Tue, Feb 20, 2018 at 08:25:21AM -0500, Paul Moore wrote:
>> On Tue, Feb 20, 2018 at 7:37 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>> > On Tue, Mar 28, 2017 at 02:30:56PM +0200, Greg Kroah-Hartman wrote:
>> >> 4.10-stable review patch. If anyone has any objections, please let me know.
>> >
>> >> + if (!(auditd_test_task(current) ||
>> >> + (current == __mutex_owner(&audit_cmd_mutex)))) {
>> >> + long stime = audit_backlog_wait_time;
>> >
>> > Since I cannot find the original email on lkml, NAK on this.
>> > __mutex_owner() is not a general purpose helper function.
>>
>> Since this code also exists in the current kernel, I need to ask what
>> recommended alternatives exist for determining the mutex owner?
>>
>> I imagine we could track the mutex owner separately in the audit
>> subsystem, but I'd much prefer to leverage an existing mechanism if
>> possible.
>
> It's not at all clear to me what that code does, I just stumbled upon
> __mutex_owner() outside of the mutex code itself and went WTF.
If you don't want people to use __mutex_owner() outside of the mutex
code I might suggest adding a rather serious comment at the top of the
function, because right now I don't see anything suggesting that
function shouldn't be used. Yes, there is the double underscore
prefix, but that can mean a few different things these days.
> The comment (aside from having the most horribly style) ...
Yeah, your dog is ugly too. Notice how neither comment is constructive?
> ... is wrong too, because it claims it will not block when we hold that lock, while,
> afaict, it will in fact do just that.
A mutex blocks when it is held, but the audit_log_start() function
should not block for the task that currently holds the
audit_cmd_mutex; that is what the comment is meant to convey. I
believe the comment makes sense, but I did write it so I'll concede
that I'm probably the not best judge. If anyone would like to offer a
different wording I'm happy to consider it.
> Maybe if you could explain how that code is supposed to work and why it
> doesn't know if it holds a lock I could make a suggestion...
I just spent a few minutes looking back over the bits available in
include/linux/mutex.h and I'm not seeing anything beyond
__mutex_owner() which would allow us to determine the mutex owning
task. It's probably easiest for us to just track ownership ourselves.
I'll put together a patch later today.
--
paul moore
www.paul-moore.com