linux-kernel - Re: [PATCH] gpu: drm: drm_mm: Fix a sleep-in-atomic-context bug in show

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Date:   Mon, 3 Sep 2018 09:52:44 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Chris Wilson <chris@...is-wilson.co.uk>
Cc:     Jia-Ju Bai <baijiaju1990@...il.com>, airlied@...ux.ie,
        gustavo@...ovan.org, maarten.lankhorst@...ux.intel.com,
        seanpaul@...omium.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        Alex Deucher <alexdeucher@...il.com>,
        amd-gfx@...ts.freedesktop.org, David Zhou <David1.Zhou@....com>,
        Christian König <christian.koenig@....com>
Subject: Re: [PATCH] gpu: drm: drm_mm: Fix a sleep-in-atomic-context bug in
 show_leaks()

On Sat, Sep 01, 2018 at 01:32:54PM +0100, Chris Wilson wrote:
> Quoting Jia-Ju Bai (2018-09-01 13:20:41)
> > The driver may sleep with holding a spinlock.
> > 
> > The function call paths (from bottom to top) in Linux-4.16 are:
> > 
> > [FUNC] kmalloc(GFP_KERNEL)
> > drivers/gpu/drm/drm_mm.c, 130: 
> >         kmalloc in show_leaks
> > drivers/gpu/drm/drm_mm.c, 913: 
> >         show_leaks in drm_mm_takedown
> > drivers/gpu/drm/drm_vma_manager.c, 107: 
> >         drm_mm_takedown in drm_vma_offset_manager_destroy
> > drivers/gpu/drm/drm_vma_manager.c, 106: 
> >         _raw_write_lock in drm_vma_offset_manager_destroy
> > 
> > [FUNC] kmalloc(GFP_KERNEL)
> > drivers/gpu/drm/drm_mm.c, 130: 
> >         kmalloc in show_leaks
> > drivers/gpu/drm/drm_mm.c, 913: 
> >         show_leaks in drm_mm_takedown
> > drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c, 71: 
> >         drm_mm_takedown in amdgpu_vram_mgr_fini
> > drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c, 70: 
> >         spin_lock in amdgpu_vram_mgr_fini
> > 
> > [FUNC] kmalloc(GFP_KERNEL)
> > drivers/gpu/drm/drm_mm.c, 130: 
> >         kmalloc in show_leaks
> > drivers/gpu/drm/drm_mm.c, 913: 
> >         show_leaks in drm_mm_takedown
> > drivers/gpu/drm/ttm/ttm_bo_manager.c, 128: 
> >         drm_mm_takedown in ttm_bo_man_takedown
> > drivers/gpu/drm/ttm/ttm_bo_manager.c, 126: 
> >         spin_lock in ttm_bo_man_takedown
> > 
> > To fix this bug, GFP_KERNEL is replaced with GFP_ATOMIC.
> 
> The bug are above, since those spinlocks do not protect the data and
> imply use-after-free.

Adding amdgpu, since that's where the bug seems to be.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch