lkml.org 
[lkml]   [2013]   [Jul]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRE: [PATCH 03/13] ACPI/IPMI: Fix race caused by the unprotected ACPI IPMI transfers
Date
> From: Corey Minyard [mailto:tcminyard@gmail.com]
> Sent: Friday, July 26, 2013 8:48 AM
>
> On 07/25/2013 07:16 PM, Zheng, Lv wrote:
> >>
> >> If I understand this correctly, the problem would be if:
> >>
> >> rem_time = wait_for_completion_timeout(&tx_msg->tx_complete,
> >> IPMI_TIMEOUT);
> >>
> >> returns on a timeout, then checks msg_done and races with something
> >> setting msg_done. If that is the case, you would need the smp_rmb()
> >> before checking msg_done.
> >>
> >> However, the timeout above is unnecessary. You are using
> >> ipmi_request_settime(), so you can set the timeout when the IPMI
> >> command fails and returns a failure message. The driver guarantees a
> >> return message for each request. Just remove the timeout from the
> >> completion, set the timeout and retries in the ipmi request, and the
> >> completion should handle the barrier issues.
> > It's just difficult for me to determine retry count and timeout value, maybe
> retry=0, timeout=IPMI_TIMEOUT is OK.
> > The code of the timeout completion is already there, I think the quick fix code
> should not introduce this logic.
> > I'll add a new patch to apply your comment.
>
> Since it is a local BMC, I doubt a retry is required. That is probably fine. Or
> you could set retry=1 and timeout=IPMI_TIMEOUT/2 if you wanted to be more
> sure, but I doubt it would make a difference. The only time you really need to
> worry about retries is if you are resetting the BMC or it is being overloaded.

I think for ACPI IPMI operation region, retries can be implemented in the ASL codes by the BIOS.
I'll check if retry=0 is correct.

>
> >
> >> Plus, from a quick glance at the code, it doesn't look like it will
> >> properly handle a situation where the timeout occurs and is handled
> >> then the response comes in later.
> > PATCH 07 fixed this issue.
> > Here we just need the smp_rmb() or holding tx_msg_lock() around the
> acpi_format_ipmi_response().
>
> If you apply the fix like I suggest, then the race goes away. If there's no
> timeout and it just waits for the completion, things get a lot simpler.

Exactly. I'll try to apply this in this patch, then the PATCH 07 is also need to be re-worked.

Thanks and best regards
-Lv


> >
> > Thanks for commenting.
>
> No problem, thanks for working on this.
>
> -corey
\
 
 \ /
  Last update: 2013-07-26 04:01    [W:0.065 / U:0.076 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site