lkml.org 
[lkml]   [2021]   [Jul]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] s390/vfio-ap: do not use open locks during VFIO_GROUP_NOTIFY_SET_KVM notification
On Tue, Jul 06, 2021 at 09:39:29AM -0400, Tony Krowiak wrote:
>
>
> On 7/5/21 10:13 AM, Jason Gunthorpe wrote:
> > On Thu, Jul 01, 2021 at 10:28:52AM -0400, Tony Krowiak wrote:
> >
> > > > I think Jason was talking about open coding locks in general.
> > > That may be so, but his comments were in support of his
> > > statement that the  mutex + wait_queue did not resolve
> > > the issue reported vai the lockdep splat because it turned
> > > off lockdep.
> > Rgiht, if this used to be proper locks and lockdep complained then
> > whatever potential deadlock it found is not magically removed by going
> > to a wait_queue. It just removes the lockdep annotations that would
> > identify the issue early.
> >
> > This is why people should not open code locks, it completely defeats
> > lockdep. That alone is merit enough for this patch.
>
> When you use the phrase "open code locks", to what are you
> specifically referring? I am confused by the use of the phrase
> "open code" in this context because open coding, at least as
> I understand it, has to do with data analysis.

"open code" here means you write the algorithm of a standard lock in
your own functions instead of calling the standard library.

Testing/setting the busy and sleeping on a wait_event is exactly a
standard lock.

Ie if I write

for (len = 0; str[len] != 0; len++)
;

Then I have open coded strlen()

Jason

\
 
 \ /
  Last update: 2021-07-06 17:13    [W:0.063 / U:0.068 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site