linux-kernel - Re: [PATCH] drm/panthor: Lock XArray when getting entries for heap and VM

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Message-ID: <Zyu8oP3a4l678uhd@e110455-lin.cambridge.arm.com>
Date: Wed, 6 Nov 2024 18:59:44 +0000
From: Liviu Dudau <liviu.dudau@....com>
To: Boris Brezillon <boris.brezillon@...labora.com>
Cc: Steven Price <steven.price@....com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	Jann Horn <jannh@...gle.com>
Subject: Re: [PATCH] drm/panthor: Lock XArray when getting entries for heap
 and VM

On Wed, Nov 06, 2024 at 02:21:33PM +0100, Boris Brezillon wrote:
> On Wed, 6 Nov 2024 13:10:37 +0000
> Liviu Dudau <liviu.dudau@....com> wrote:
> 
> > panthor_heap_pool_release() does not take the panthor_heap_pool::lock, so the protection
> > is not really there. I could fix panthor_heap_pool_release() and then add a
> > lockdep_assert_held() before both calls to xa_load() if you think that's a better
> > solution.
> 
> Hm, but panthor_heap_pool_release() doesn't release the heap contexts,
> it just calls xa_destroy(). If we have objects remaining in the xarray,
> they'll be leaked, but that's not a race. BTW, can we make this two
> separate patches. I feel like the thing on the vm is an actual fix,
> while the second one (adding a helper with a lockdep_assert()) is
> safety net that's worth having, but not necessarily something we need
> to backport.

I've decided to drop the panthor_heap.c changes as Boris is right, the pool->lock
should be enough. Adding a lockdep_assert() right after the down_write() call
also feels a bit silly, so I did not bother with it.

Best regards,
Liviu

-- 
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