On Fri, 6 Jan 2006, david singleton wrote:
> > Here is a new patch that provides both futex deadlock detection and > prevents ill-behaved and > malicious apps from deadlocking the kernel through the robust futex > interface. > > http://source.mvista.com/~dsingleton/patch-2.6.15-rt2-rf1 > > Deadlock detection is done 'up front' for both POSIX and robust > pthread_mutexes. Non-recursive > POSIX mutexes will hang if deadlocked, as defined by the POSIX spec. > The wait channel they > are hung on is 'futex_deadlock'. This wait channel makes it easy to > spot that your POSIX app > has deadlocked itself via the 'ps' command. > > Robust futexes will have -EDEADLK returned to them since there is no > POSIX specification for > robust mutexes, yet, and returning -EDEADLK is more in the spirit of > robustness. Robust > mutexes are cleaned up by the kernel after a thread dies and they also > report to the app if > it is deadlocking itself. > > Deadlock detection is something I have wanted to provide for both debug > and production kernels > for a while. It was previously available through DEBUG_DEADLOCKS. I > needed to add the > deadlock dection code for both production and debug kernels to prevent > applications hanging > the kernel. > I am a little bit confused when I read check_futex_deadlock(): It takes a parameter struct thread_info *ti and immediately do struct task_struct *task = ti->task. Now we have the usual pair (thread_info *ti, task_t *task) corresponding to the same process. Later on in the function you do ti = lock_owner(lock), but do not update task. Was this intented? Anyway, I can't see that you have locked the necesary raw_spin_locks. Forinstance lock_owner(lock) must be called with the lock->wait_lock taken and task->blocked_on needs task->pi_lock locked. To avoid deadlocks in all the deadlock detection you have to do the loop something like for(owner = current; owner; ) { raw_spin_lock(&owner->pi_lock); if(owner->task->blocked_on) { lock = owner->task->blocked_on->lock; raw_spin_lock(&lock->wait_lock); owner2 = lock_owner(lock); if(owner2) { get_task_struct(owner2->task); raw_spin_unlock(&lock->wait_lock) raw_spin_unlock(&owner->pi_lock); } put_task_struct(owner->task); owner = owner2; if(owner2==current) DEADLOCK } Esben > David > > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to [EMAIL PROTECTED] > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >
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