Messages in this thread | | | Date | Wed, 18 Nov 2009 17:43:03 +0800 | From | Lai Jiangshan <> | Subject | Re: [PATCH 2/2] lockdep: Don't only check recursive read locks once in a sequence |
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Frederic Weisbecker wrote: > Say we have the following locks: > A (rwlock, Aw: writelock, Ar: recursive read lock) > B (normal lock) > > and the following sequences: > Ar -> B -> Ar > Aw -> B > > This won't be detected as a lock inversion
""" read-preference <==> read-recursive ability (rwlock) otherwise ==> read-recursive disability (rwsem) """
If "B -> Ar" is always after "Ar", it's NOT a really lock inversion because rwlock is read-preference, we can ignore all "Ar" which are after "B".
If sometimes "B -> Ar" is not after "Ar", then we have these sequences: B -> Ar Aw -> B
Lockdep can detects it now(without this patch applied).
Maybe I have misunderstood your patch.
> because in the sequence > of locks held by the current task, if we have a same class acquired > as read-recursive several times, only the first one will be checked > in the tree (although all of them are checked for deadlocks in the > current held sequence). > > Fix it by always adding recursive read locks in the dependency tree. > > Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Ming Lei <tom.leiming@gmail.com> > --- > kernel/lockdep.c | 4 ++-- > 1 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/kernel/lockdep.c b/kernel/lockdep.c > index a6f7440..13d1d54 100644 > --- a/kernel/lockdep.c > +++ b/kernel/lockdep.c > @@ -1949,9 +1949,9 @@ static int validate_chain(struct task_struct *curr, struct lockdep_map *lock, > hlock->read = 2; > /* > * Add dependency only if this lock is not the head > - * of the chain, and if it's not a secondary read-lock: > + * of the chain. > */ > - if (!chain_head && ret != 2) > + if (!chain_head) > if (!check_prevs_add(curr, hlock)) > return 0; > graph_unlock();
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