Re: [PATCH] drm: Avoid drm_global_mutex for simple inc/dec of dev->open_count

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On 1/24/20 7:39 PM, Chris Wilson wrote:
Quoting Thomas Hellström (VMware) (2020-01-24 13:37:47)
On 1/24/20 2:01 PM, Chris Wilson wrote:
Since drm_global_mutex is a true global mutex across devices, we don't
want to acquire it unless absolutely necessary. For maintaining the
device local open_count, we can use atomic operations on the counter
itself, except when making the transition to/from 0. Here, we tackle the
easy portion of delaying acquiring the drm_global_mutex for the final
release by using atomic_dec_and_mutex_lock(), leaving the global
serialisation across the device opens.

Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Thomas Hellström (VMware) <thomas_os@xxxxxxxxxxxx>
For the series:

Reviewed-by: Thomas Hellström <thellstrom@xxxxxxxxxx>
Now being opt-in, it is fairly limited in scope and will not randomly
break others (touch wood) and the close() racing in BAT didn't throw
anything up, so pushed to drm-misc-next. Thanks for the review and
suggestions,

Next task is to suggest others might like to use it as well.
-Chris

Thanks. I'll look at doing the same for those drivers I audited.

/Thomas


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