linux-kernel - Re: linux-next: manual merge of the tip tree with the drm-intel tree

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Date:   Tue, 8 Nov 2016 11:44:03 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Stephen Rothwell <sfr@...b.auug.org.au>
Cc:     Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Intel Graphics <intel-gfx@...ts.freedesktop.org>,
        DRI <dri-devel@...ts.freedesktop.org>,
        linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
        Chris Wilson <chris@...is-wilson.co.uk>
Subject: Re: linux-next: manual merge of the tip tree with the drm-intel tree

On Tue, Nov 08, 2016 at 03:25:41PM +1100, Stephen Rothwell wrote:
> Hi all,
> 
> FIXME: Add owner of second tree to To:
>        Add author(s)/SOB of conflicting commits.
> 
> Today's linux-next merge of the tip tree got a conflict in:
> 
>   drivers/gpu/drm/i915/i915_gem_shrinker.c
> 
> between commits:
> 
>   1233e2db199d ("drm/i915: Move object backing storage manipulation to its own locking")
> 
> from the drm-intel tree and commit:
> 
>   3ab7c086d5ec ("locking/drm: Kill mutex trickery")
>   c7faee2109f9 ("locking/drm: Fix i915_gem_shrinker_lock() locking")

Hm, this seems to be the older versions that nuke the recursive locking
trickery entirely, I thought we had version in-flight that kept that? I
know that the i915 (and msm locking fwiw) is horrible since essentially
it's a recursive BKL, and we're working (slowly, after all getting rid of
the BKL wasn't simple either) to fix this. But meanwhile I'm assuming that
we'll still need this to be able to get out of low memory situations in
i915. Has that part simply not yet landed?

Thanks, Daniel

> 
> from the tip tree.
> 
> I fixed it up (see below) and can carry the fix as necessary. This
> is now fixed as far as linux-next is concerned, but any non trivial
> conflicts should be mentioned to your upstream maintainer when your tree
> is submitted for merging.  You may also want to consider cooperating
> with the maintainer of the conflicting tree to minimise any particularly
> complex conflicts.
> 
> -- 
> Cheers,
> Stephen Rothwell
> 
> diff --cc drivers/gpu/drm/i915/i915_gem_shrinker.c
> index a6fc1bdc48af,e9bd2a81d03a..000000000000
> --- a/drivers/gpu/drm/i915/i915_gem_shrinker.c
> +++ b/drivers/gpu/drm/i915/i915_gem_shrinker.c
> @@@ -35,33 -35,6 +35,15 @@@
>   #include "i915_drv.h"
>   #include "i915_trace.h"
>   
> - static bool mutex_is_locked_by(struct mutex *mutex, struct task_struct *task)
> - {
> - 	if (!mutex_is_locked(mutex))
> - 		return false;
> - 
> - #if defined(CONFIG_DEBUG_MUTEXES) || defined(CONFIG_MUTEX_SPIN_ON_OWNER)
> - 	return mutex->owner == task;
> - #else
> - 	/* Since UP may be pre-empted, we cannot assume that we own the lock */
> - 	return false;
> - #endif
> - }
> - 
>  +static bool i915_gem_shrinker_lock(struct drm_device *dev, bool *unlock)
>  +{
> - 	if (!mutex_trylock(&dev->struct_mutex)) {
> - 		if (!mutex_is_locked_by(&dev->struct_mutex, current))
> - 			return false;
> - 
> - 		*unlock = false;
> - 	} else {
> - 		*unlock = true;
> - 	}
> ++	if (!mutex_trylock(&dev->struct_mutex))
> ++		return false;
>  +
> ++	*unlock = true;
>  +	return true;
>  +}
>  +
>   static bool any_vma_pinned(struct drm_i915_gem_object *obj)
>   {
>   	struct i915_vma *vma;

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch