From: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
To: 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
Cc: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>,
dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
intel-gfx@lists.freedesktop.org, skhan@linuxfoundation.org,
gregkh@linuxfoundation.org,
linux-kernel-mentees@lists.linuxfoundation.org,
linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org,
Daniel Vetter <daniel.vetter@ffwll.ch>
Subject: [PATCH v10 3/4] drm: lock drm_global_mutex earlier in the ioctl handler
Date: Tue, 31 Aug 2021 15:25:00 +0800 [thread overview]
Message-ID: <20210831072501.184211-4-desmondcheongzx@gmail.com> (raw)
In-Reply-To: <20210831072501.184211-1-desmondcheongzx@gmail.com>
In a future patch, a read lock on drm_device.master_rwsem is
held in the ioctl handler before the check for ioctl
permissions. However, this inverts the lock hierarchy of
drm_global_mutex --> master_rwsem.
To avoid this, we do some prep work to grab the drm_global_mutex
before checking for ioctl permissions.
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
drivers/gpu/drm/drm_ioctl.c | 21 ++++++++++++---------
1 file changed, 12 insertions(+), 9 deletions(-)
diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
index 9fc00e36c5d6..fe9c4c0264a9 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -767,24 +767,27 @@ long drm_ioctl_kernel(struct file *file, drm_ioctl_t *func, void *kdata,
{
struct drm_file *file_priv = file->private_data;
struct drm_device *dev = file_priv->minor->dev;
+ bool locked_ioctl;
int retcode;
if (drm_dev_is_unplugged(dev))
return -ENODEV;
+ /* Enforce sane locking for modern driver ioctls. */
+ locked_ioctl = (unlikely(drm_core_check_feature(dev, DRIVER_LEGACY)) &&
+ !(flags & DRM_UNLOCKED));
+ if (locked_ioctl)
+ mutex_lock(&drm_global_mutex);
+
retcode = drm_ioctl_permit(flags, file_priv);
if (unlikely(retcode))
- return retcode;
+ goto out;
- /* Enforce sane locking for modern driver ioctls. */
- if (likely(!drm_core_check_feature(dev, DRIVER_LEGACY)) ||
- (flags & DRM_UNLOCKED))
- retcode = func(dev, kdata, file_priv);
- else {
- mutex_lock(&drm_global_mutex);
- retcode = func(dev, kdata, file_priv);
+ retcode = func(dev, kdata, file_priv);
+
+out:
+ if (locked_ioctl)
mutex_unlock(&drm_global_mutex);
- }
return retcode;
}
EXPORT_SYMBOL(drm_ioctl_kernel);
--
2.25.1
next prev parent reply other threads:[~2021-08-31 7:25 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-31 7:24 [PATCH v10 0/4] drm: update locking for modesetting Desmond Cheong Zhi Xi
2021-08-31 7:24 ` [PATCH v10 1/4] drm: fix null ptr dereference in drm_master_release Desmond Cheong Zhi Xi
2021-08-31 7:24 ` [PATCH v10 2/4] drm: convert drm_device.master_mutex into a rwsem Desmond Cheong Zhi Xi
2021-08-31 7:25 ` Desmond Cheong Zhi Xi [this message]
2021-08-31 7:25 ` [PATCH v10 4/4] drm: avoid races with modesetting rights Desmond Cheong Zhi Xi
2021-09-07 19:50 ` [PATCH v10 0/4] drm: update locking for modesetting Desmond Cheong Zhi Xi
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