Messages in this thread | | | Subject | Re: [RFC][PATCH 7/7] lockdep: spin_lock_nest_lock() | From | Peter Zijlstra <> | Date | Mon, 04 Aug 2008 20:54:06 +0200 |
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On Mon, 2008-08-04 at 11:06 -0700, Jeremy Fitzhardinge wrote: > Peter Zijlstra wrote: > > Expose the new lock protection lock. > > > > This can be used to annotate places where we take multiple locks of the > > same class and avoid deadlocks by always taking another (top-level) lock > > first. > > > > OK, so the expected usage is: > > spin_lock(&outer_lock); > /* take in any order */ > spin_lock_nest_lock(&inner[0], &outer_lock); > spin_lock_nest_lock(&inner[2], &outer_lock); > spin_lock_nest_lock(&inner[1], &outer_lock); > ... > > ?
Yes (there it no requirement that the outer lock is a spinlock_t, just that it has a ->dep_map member - so: mutex, rwsem and spinlock will do).
> And it's OK to > > 1. take inner locks one at a time without holding the outer lock
Yes
> 2. use plain spin_lock on inner locks when you're taking them one at > a time, and
Yes
> 3. release the outer lock before releasing the inner locks
Only if you then release the inner locks in the reverse order you took them - the nested release code (releasing a lock that is not on the top of the stack) basically pops and pushes all the locks, the push will fail if the outer lock is released.
> but it's not OK to try to use different outer locks for a given inner lock.
It doesn't validate this part - as with most lockdep annotations you can annotate away real deadlocks.
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