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

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Message-ID: <20241106142133.09378b5a@collabora.com>
Date: Wed, 6 Nov 2024 14:21:33 +0100
From: Boris Brezillon <boris.brezillon@...labora.com>
To: Liviu Dudau <liviu.dudau@....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, 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.