diff options
authorStefan Richter <stefanr@s5r6.in-berlin.de>2008-10-26 12:03:37 +0100
committerStefan Richter <stefanr@s5r6.in-berlin.de>2008-10-31 08:48:26 +0100
commit638570b54346f140bc09b986d93e76025d35180f (patch)
parent233976e539a93de1320fc7625b24076b1f9e2c9c (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>
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,
- mutex_lock(&fi->state_mutex);
+ if (!mutex_trylock(&fi->state_mutex))
+ return -EAGAIN;
switch (fi->iso_state) {