Messages in this thread | | | Date | Mon, 18 Apr 2011 21:34:05 +0800 | From | Yong Zhang <> | Subject | Re: [RFC][PATCH 3/7] lockdep: Annotate read/write states |
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On Sun, Apr 17, 2011 at 11:45:08AM +0200, Peter Zijlstra wrote: > From: Gautham R Shenoy <ego@in.ibm.com> > > Currently we do not save the recursive read dependencies in the dependency > chain. As a result, a deadlock caused by the following chains are not spotted, > since we never have the chain 1 in our dependency list: > > 1: Rlock(A) --> lock(B) > 2: lock(B) --> Wlock(A), where A is a recursive read lock. > > Before adding the Recursive Read locks to the dependency chains, we need to > distinguish them from the normal read locks since the conflicting states for > these two are quite different. > > Currently the read/write status of a lock while it's acquired is denoted by a > monotonically increasing variable where: > > 0 - WRITE > 1 - READ > 2 - RECURSIVE READ > > In this patch, we propose to modify this distinction from a monotonically > increasing variable to a bit mask where: > > 0x1 - WRITE > 0x2 - READ > 0x4 - RECURSIVE READ > > This helps us to define the conflicting states for each lock with ease: > Thereby, the conflicting states for a given states are defined as follows: > > Conflicting_states(WRITE): RECURSIVE_READ | READ | WRITE > Conflicting_states(READ): READ | WRITE > Conflicting_states(RECURSIVE_READ): WRITE > > Also, we use one more bit in the bitmask to distinguish the first recursive > read in the current chain from the others, since it is sufficient to add only > this dependency to the dependency list. > > Signed-off-by: Gautham R Shenoy <ego@in.ibm.com> > Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> > --- > include/linux/lockdep.h | 107 ++++++++++++++++++++++++++++++++++++------------ > kernel/lockdep.c | 46 ++++++++++---------- > 2 files changed, 105 insertions(+), 48 deletions(-) > > @@ -2273,7 +2273,7 @@ mark_held_locks(struct task_struct *curr > hlock = curr->held_locks + i; > > usage_bit = 2 + (mark << 2); /* ENABLED */ > - if (hlock->read) > + if (hlock->rw_state)
is_read(hlock->rw_state) ?
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