From: Daniel Vetter <daniel@ffwll.ch>
To: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
Cc: maarten.lankhorst@linux.intel.com, mripard@kernel.org,
tzimmermann@suse.de, airlied@linux.ie, daniel@ffwll.ch,
sumit.semwal@linaro.org, christian.koenig@amd.com,
axboe@kernel.dk, oleg@redhat.com, tglx@linutronix.de,
dvyukov@google.com, walter-zh.wu@mediatek.com,
dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
intel-gfx@lists.freedesktop.org, linux-media@vger.kernel.org,
linaro-mm-sig@lists.linaro.org, skhan@linuxfoundation.org,
gregkh@linuxfoundation.org,
linux-kernel-mentees@lists.linuxfoundation.org,
kernel test robot <lkp@intel.com>
Subject: Re: [PATCH v3 8/9] kernel: export task_work_add
Date: Wed, 18 Aug 2021 13:06:36 +0200 [thread overview]
Message-ID: <YRzpvHBQuq0kFtzH@phenom.ffwll.local> (raw)
In-Reply-To: <20210818073824.1560124-9-desmondcheongzx@gmail.com>
On Wed, Aug 18, 2021 at 03:38:23PM +0800, Desmond Cheong Zhi Xi wrote:
> The task_work_add function is needed to prevent userspace races with
> DRM modesetting rights.
>
> Some DRM ioctls can change modesetting permissions while other
> concurrent users are performing modesetting. To prevent races with
> userspace, such functions should flush readers of old permissions
> before returning to user mode. As the function that changes
> permissions might itself be a reader of the old permissions, we intend
> to schedule this flush using task_work_add.
>
> However, when DRM is compiled as a loadable kernel module without
> exporting task_work_add, we get the following compilation error:
>
> ERROR: modpost: "task_work_add" [drivers/gpu/drm/drm.ko] undefined!
>
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
Just realized another benefit of pushing the dev->master_rwsem write
locks down into ioctls that need them: We wouldn't need this function here
exported for use in drm. But also I'm not sure that works any better than
the design in your current patch set ...
-Daniel
> ---
> kernel/task_work.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/kernel/task_work.c b/kernel/task_work.c
> index 1698fbe6f0e1..90000404af2b 100644
> --- a/kernel/task_work.c
> +++ b/kernel/task_work.c
> @@ -60,6 +60,7 @@ int task_work_add(struct task_struct *task, struct callback_head *work,
>
> return 0;
> }
> +EXPORT_SYMBOL(task_work_add);
>
> /**
> * task_work_cancel_match - cancel a pending work added by task_work_add()
> --
> 2.25.1
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
next prev parent reply other threads:[~2021-08-18 11:06 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-18 7:38 [PATCH v3 0/9] drm, kernel: update locking for DRM Desmond Cheong Zhi Xi
2021-08-18 7:38 ` [PATCH v3 1/9] drm: move master_lookup_lock into drm_device Desmond Cheong Zhi Xi
2021-08-18 7:38 ` [PATCH v3 2/9] drm: hold master_lookup_lock when releasing a drm_file's master Desmond Cheong Zhi Xi
2021-08-18 10:05 ` Daniel Vetter
2021-08-18 14:50 ` Desmond Cheong Zhi Xi
2021-08-18 7:38 ` [PATCH v3 3/9] drm: check for null master in drm_is_current_master_locked Desmond Cheong Zhi Xi
2021-08-18 10:04 ` Daniel Vetter
2021-08-18 7:38 ` [PATCH v3 4/9] drm: fix potential null ptr dereferences in drm_{auth,ioctl} Desmond Cheong Zhi Xi
2021-08-18 10:11 ` Daniel Vetter
2021-08-18 15:37 ` Desmond Cheong Zhi Xi
2021-08-18 16:33 ` [Intel-gfx] [PATCH v3 4/9] drm: fix potential null ptr dereferences in drm_{auth, ioctl} Daniel Vetter
2021-08-19 5:31 ` Desmond Cheong Zhi Xi
2021-08-18 7:38 ` [PATCH v3 5/9] drm: protect magic_map,unique{_len} with master_lookup_lock Desmond Cheong Zhi Xi
2021-08-18 10:43 ` Daniel Vetter
2021-08-18 7:38 ` [PATCH v3 6/9] drm: convert drm_device.master_mutex into a rwsem Desmond Cheong Zhi Xi
2021-08-18 7:38 ` [PATCH v3 7/9] drm: update global mutex lock in the ioctl handler Desmond Cheong Zhi Xi
2021-08-18 11:02 ` Daniel Vetter
2021-08-19 10:52 ` Desmond Cheong Zhi Xi
2021-08-19 11:21 ` [Intel-gfx] " Daniel Vetter
2021-08-18 7:38 ` [PATCH v3 8/9] kernel: export task_work_add Desmond Cheong Zhi Xi
2021-08-18 11:06 ` Daniel Vetter [this message]
2021-08-19 9:26 ` Christoph Hellwig
2021-08-19 9:40 ` Desmond Cheong Zhi Xi
2021-08-18 7:38 ` [PATCH v3 9/9] drm: avoid races with modesetting rights Desmond Cheong Zhi Xi
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