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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>
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| .. | ||
| config_roms.c | ||
| config_roms.h | ||
| csr.c | ||
| csr.h | ||
| csr1212.c | ||
| csr1212.h | ||
| dma.c | ||
| dma.h | ||
| dv1394-private.h | ||
| dv1394.c | ||
| dv1394.h | ||
| eth1394.c | ||
| eth1394.h | ||
| highlevel.c | ||
| highlevel.h | ||
| hosts.c | ||
| hosts.h | ||
| ieee1394-ioctl.h | ||
| ieee1394.h | ||
| ieee1394_core.c | ||
| ieee1394_core.h | ||
| ieee1394_hotplug.h | ||
| ieee1394_transactions.c | ||
| ieee1394_transactions.h | ||
| ieee1394_types.h | ||
| init_ohci1394_dma.c | ||
| iso.c | ||
| iso.h | ||
| Kconfig | ||
| Makefile | ||
| nodemgr.c | ||
| nodemgr.h | ||
| ohci1394.c | ||
| ohci1394.h | ||
| pcilynx.c | ||
| pcilynx.h | ||
| raw1394-private.h | ||
| raw1394.c | ||
| raw1394.h | ||
| sbp2.c | ||
| sbp2.h | ||
| video1394.c | ||
| video1394.h | ||