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| author | Stefan Richter <stefanr@s5r6.in-berlin.de> | 2008-10-26 12:02:03 +0100 |
|---|---|---|
| committer | Stefan Richter <stefanr@s5r6.in-berlin.de> | 2008-10-31 08:48:26 +0100 |
| commit | 8449fc3ae58bf8ee5acbd2280754cde67b5db128 (patch) | |
| tree | 01c632f8b1adf31f937a67f1e2d000053eea1f1a /drivers/ieee1394 | |
| parent | 638570b54346f140bc09b986d93e76025d35180f (diff) | |
| download | lwn-8449fc3ae58bf8ee5acbd2280754cde67b5db128.tar.gz lwn-8449fc3ae58bf8ee5acbd2280754cde67b5db128.zip | |
ieee1394: dv1394: fix possible deadlock in multithreaded clients
Fix a possible though highly unlikely deadlock:
Thread A: Thread B:
- acquire mmap_sem - dv1394_ioctl/read/write()
- dv1394_mmap() - acquire video->mtx
- acquire video->mtx - copy_to/from_user(), possible page fault:
acquire mmap_sem
The simplest fix is to use mutex_trylock() instead of mutex_lock() in
dv1394_mmap(). This changes the behavior under contention in a way
which is visible to userspace clients. However, my guess is that no
clients exist which use mmap vs. ioctl/read/write on the dv1394
character device file interface in concurrent threads.
Reported-by: Johannes Weiner <hannes@saeurebad.de>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Diffstat (limited to 'drivers/ieee1394')
| -rw-r--r-- | drivers/ieee1394/dv1394.c | 10 |
1 files changed, 8 insertions, 2 deletions
diff --git a/drivers/ieee1394/dv1394.c b/drivers/ieee1394/dv1394.c index df70f51279d8..53329972c7db 100644 --- a/drivers/ieee1394/dv1394.c +++ b/drivers/ieee1394/dv1394.c @@ -1270,8 +1270,14 @@ static int dv1394_mmap(struct file *file, struct vm_area_struct *vma) struct video_card *video = file_to_video_card(file); int retval = -EINVAL; - /* serialize mmap */ - mutex_lock(&video->mtx); + /* + * We cannot use the blocking variant mutex_lock here because .mmap + * is called with mmap_sem held, while .ioctl, .read, .write acquire + * video->mtx and subsequently call copy_to/from_user which will + * grab mmap_sem in case of a page fault. + */ + if (!mutex_trylock(&video->mtx)) + return -EAGAIN; if ( ! video_card_initialized(video) ) { retval = do_dv1394_init_default(video); |