diff options
| author | Stefan Richter <stefanr@s5r6.in-berlin.de> | 2008-10-26 12:03:37 +0100 |
|---|---|---|
| committer | Stefan Richter <stefanr@s5r6.in-berlin.de> | 2008-10-31 08:48:26 +0100 |
| commit | 638570b54346f140bc09b986d93e76025d35180f (patch) | |
| tree | b3ffd423bcabe679cb5d218d9f4d2aed4a9ae50e /drivers | |
| parent | 233976e539a93de1320fc7625b24076b1f9e2c9c (diff) | |
ieee1394: raw1394: fix possible deadlock in multithreaded clients
Regression in 2.6.28-rc1: When I added the new state_mutex which
prevents corruption of raw1394's internal state when accessed by
multithreaded client applications, the following possible though
highly unlikely deadlock slipped in:
Thread A: Thread B:
- acquire mmap_sem - raw1394_write() or raw1394_ioctl()
- raw1394_mmap() - acquire state_mutex
- acquire state_mutex - copy_to/from_user(), possible page fault:
acquire mmap_sem
The simplest fix is to use mutex_trylock() instead of mutex_lock() in
raw1394_mmap(). This changes the behavior under contention in a way
which is visible to userspace clients. However, since multithreaded
access was entirely buggy before state_mutex was added and libraw1394's
documentation advised application programmers to use a handle only in a
single thread, this change in behaviour should not be an issue in
practice at all.
Since we have to use mutex_trylock() in raw1394_mmap() regardless
whether /dev/raw1394 was opened with O_NONBLOCK or not, we now use
mutex_trylock() unconditionally everywhere for state_mutex, just to have
consistent behavior.
Reported-by: Johannes Weiner <hannes@saeurebad.de>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/ieee1394/raw1394.c | 9 |
1 files changed, 6 insertions, 3 deletions
diff --git a/drivers/ieee1394/raw1394.c b/drivers/ieee1394/raw1394.c index 2cf4ae75bec..4bdfff0a919 100644 --- a/drivers/ieee1394/raw1394.c +++ b/drivers/ieee1394/raw1394.c @@ -2268,7 +2268,8 @@ static ssize_t raw1394_write(struct file *file, const char __user * buffer, return -EFAULT; } - mutex_lock(&fi->state_mutex); + if (!mutex_trylock(&fi->state_mutex)) + return -EAGAIN; switch (fi->state) { case opened: @@ -2548,7 +2549,8 @@ static int raw1394_mmap(struct file *file, struct vm_area_struct *vma) struct file_info *fi = file->private_data; int ret; - mutex_lock(&fi->state_mutex); + if (!mutex_trylock(&fi->state_mutex)) + return -EAGAIN; if (fi->iso_state == RAW1394_ISO_INACTIVE) ret = -EINVAL; @@ -2669,7 +2671,8 @@ static long raw1394_ioctl(struct file *file, unsigned int cmd, break; } - mutex_lock(&fi->state_mutex); + if (!mutex_trylock(&fi->state_mutex)) + return -EAGAIN; switch (fi->iso_state) { case RAW1394_ISO_INACTIVE: |