Messages in this thread | | | Subject | Re: [RFC 3/3] mutex: When there is no owner, stop spinning after too many tries | From | Jason Low <> | Date | Wed, 15 Jan 2014 22:46:17 -0800 |
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On Thu, 2014-01-16 at 10:14 +0700, Linus Torvalds wrote: > On Thu, Jan 16, 2014 at 9:45 AM, Jason Low <jason.low2@hp.com> wrote: > > > > Any comments on the below change which unlocks the mutex before taking > > the lock->wait_lock to wake up a waiter? Thanks. > > Hmm. Doesn't that mean that a new lock owner can come in *before* > you've called debug_mutex_unlock and the lockdep stuff, and get the > lock? And then debug_mutex_lock() will be called *before* the unlocker > called debug_mutex_unlock(), which I'm sure confuses things.
If obtaining the wait_lock for debug_mutex_unlock is the issue, then perhaps we can address that by taking care of #ifdef CONFIG_DEBUG_MUTEXES. In the CONFIG_DEBUG_MUTEXES case, we can take the wait_lock first, and in the regular case, take the wait_lock after releasing the mutex.
#ifdef CONFIG_DEBUG_MUTEXES spin_lock_mutex(&lock->wait_lock, flags); #endif
mutex_release(&lock->dep_map, nested, _RET_IP_); debug_mutex_unlock(lock); if (__mutex_slowpath_needs_to_unlock()) atomic_set(&lock->count, 1);
#ifndef CONFIG_DEBUG_MUTEXES spin_lock_mutex(&lock->wait_lock, flags); #endif
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