linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
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, intel-gfx@lists.freedesktop.org,
	linux-kernel@vger.kernel.org, linux-media@vger.kernel.org,
	linaro-mm-sig@lists.linaro.org, skhan@linuxfoundation.org,
	gregkh@linuxfoundation.org,
	linux-kernel-mentees@lists.linuxfoundation.org,
	emil.l.velikov@gmail.com
Subject: [PATCH v6 2/4] drm: avoid circular locks in __drm_mode_object_find
Date: Wed, 30 Jun 2021 22:54:02 +0800	[thread overview]
Message-ID: <20210630145404.5958-3-desmondcheongzx@gmail.com> (raw)
In-Reply-To: <20210630145404.5958-1-desmondcheongzx@gmail.com>

In a future patch, _drm_lease_held will dereference drm_file->master
only after making a call to drm_file_get_master which increments the
reference count of drm_file->master while holding a lock on
drm_device.master_mutex.

In preparation for this, the call to _drm_lease_held should be moved
out from the section locked by &dev->mode_config.idr_mutex. This
avoids inverting the lock hierarchy for
&dev->master_mutex --> &dev->mode_config.idr_mutex

Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
---
 drivers/gpu/drm/drm_mode_object.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_mode_object.c b/drivers/gpu/drm/drm_mode_object.c
index b26588b52795..63d35f1f98dd 100644
--- a/drivers/gpu/drm/drm_mode_object.c
+++ b/drivers/gpu/drm/drm_mode_object.c
@@ -146,16 +146,18 @@ struct drm_mode_object *__drm_mode_object_find(struct drm_device *dev,
 	if (obj && obj->id != id)
 		obj = NULL;
 
-	if (obj && drm_mode_object_lease_required(obj->type) &&
-	    !_drm_lease_held(file_priv, obj->id))
-		obj = NULL;
-
 	if (obj && obj->free_cb) {
 		if (!kref_get_unless_zero(&obj->refcount))
 			obj = NULL;
 	}
 	mutex_unlock(&dev->mode_config.idr_mutex);
 
+	if (obj && drm_mode_object_lease_required(obj->type) &&
+		!_drm_lease_held(file_priv, obj->id)) {
+		drm_mode_object_put(obj);
+		obj = NULL;
+	}
+
 	return obj;
 }
 
-- 
2.25.1


  parent reply	other threads:[~2021-06-30 14:55 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-30 14:54 [PATCH v6 0/4] drm: address potential UAF bugs with drm_master ptrs Desmond Cheong Zhi Xi
2021-06-30 14:54 ` [PATCH v6 1/4] drm: avoid circular locks in drm_mode_getconnector Desmond Cheong Zhi Xi
2021-06-30 14:54 ` Desmond Cheong Zhi Xi [this message]
2021-06-30 14:54 ` [PATCH v6 3/4] drm: add a locked version of drm_is_current_master Desmond Cheong Zhi Xi
2021-06-30 14:54 ` [PATCH v6 4/4] drm: protect drm_master pointers in drm_lease.c Desmond Cheong Zhi Xi

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210630145404.5958-3-desmondcheongzx@gmail.com \
    --to=desmondcheongzx@gmail.com \
    --cc=airlied@linux.ie \
    --cc=christian.koenig@amd.com \
    --cc=daniel@ffwll.ch \
    --cc=dri-devel@lists.freedesktop.org \
    --cc=emil.l.velikov@gmail.com \
    --cc=gregkh@linuxfoundation.org \
    --cc=intel-gfx@lists.freedesktop.org \
    --cc=linaro-mm-sig@lists.linaro.org \
    --cc=linux-kernel-mentees@lists.linuxfoundation.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-media@vger.kernel.org \
    --cc=maarten.lankhorst@linux.intel.com \
    --cc=mripard@kernel.org \
    --cc=skhan@linuxfoundation.org \
    --cc=sumit.semwal@linaro.org \
    --cc=tzimmermann@suse.de \
    --subject='Re: [PATCH v6 2/4] drm: avoid circular locks in __drm_mode_object_find' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).