diff options
author | Laurent Pinchart <laurent.pinchart@skynet.be> | 2008-07-11 19:32:15 -0300 |
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committer | Mauro Carvalho Chehab <mchehab@infradead.org> | 2008-07-20 07:19:31 -0300 |
commit | a9e285856112e5e721b6a341d15437a164128b30 (patch) | |
tree | 23b1dab5ebf87625e037eb0d6d09dc7a5d7add1c /drivers/ata/sata_nv.c | |
parent | 6f80e1b4cda7e184e369c84a8b388882b0233d53 (diff) |
V4L/DVB (8257): uvcvideo: Fix possible AB-BA deadlock with videodev_lock and open_mutex
The uvcvideo driver's uvc_v4l2_open() method is called from videodev's
video_open() function, which means it is called with the videodev_lock
mutex held. uvc_v4l2_open() then takes uvc_driver.open_mutex to check
dev->state and avoid racing against a device disconnect, which means
that open_mutex must nest inside videodev_lock.
However uvc_disconnect() takes the open_mutex around setting
dev->state and also around putting its device reference. However, if
uvc_disconnect() ends up dropping the last reference, it will call
uvc_delete(), which calls into the videodev code to unregister its
device, and this will end up taking videodev_lock. This opens a
(unlikely in practice) window for an AB-BA deadlock and also causes a
lockdep warning because of the lock misordering.
Fortunately there is no apparent reason to hold open_mutex when doing
kref_put() in uvc_disconnect(): if uvc_v4l2_open() runs before the
state is set to UVC_DEV_DISCONNECTED, then it will take another
reference to the device and kref_put() won't call uvc_delete; if
uvc_v4l2_open() runs after the state is set, it will run before
uvc_delete(), see the state, and return immediately -- uvc_delete()
does uvc_unregister_video() (and hence video_unregister_device(),
which is synchronized with videodev_lock) as its first thing, so there
is no risk of use-after-free in uvc_v4l2_open().
Bug diagnosed based on a lockdep warning reported by Romano Giannetti
<romano@dea.icai.upcomillas.es>.
Signed-off-by: Roland Dreier <roland@digitalvampire.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart@skynet.be>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>
Diffstat (limited to 'drivers/ata/sata_nv.c')
0 files changed, 0 insertions, 0 deletions