On Thu, Jun 5, 2014 at 8:31 AM, Trond Myklebust <[email protected]> wrote: > This commit reverts the addition of lockdep checking to raw_seqcount_begin > for the following reasons: > > 1) It violates the naming convention that raw_* functions should not > do lockdep checks (a convention that is also followed by the other > raw_*_seqcount_begin functions). > 2) raw_seqcount_begin does not spin, so it can only be part of an ABBA > deadlock in very special circumstances (for instance if a lock > is held across the entire raw_seqcount_begin()+read_seqcount_retry() > loop while also being taken inside the write_seqcount protected area). > 3) It is causing false positives with some existing callers, and there > is no non-lockdep alternative for those callers to use. > > None of the three existing callers (__d_lookup_rcu, netdev_get_name, and > the NFS state code) appear to use the function in a manner that is ABBA > deadlock prone. > > Fixes: 1ca7d67cf5d5: seqcount: Add lockdep functionality to seqcount/seqlock > Cc: John Stultz <[email protected]> > Cc: Peter Zijlstra <[email protected]> > Cc: Ingo Molnar <[email protected]> > Cc: "David S. Miller" <[email protected]> > Cc: Al Viro <[email protected]> > Link: > http://lkml.kernel.org/r/cahqdgtrr6svehxiqwo24houh9au9cl82z8z-d8-7u951f_d...@mail.gmail.com > Signed-off-by: Trond Myklebust <[email protected]> > --- > include/linux/seqlock.h | 2 -- > 1 file changed, 2 deletions(-) > > diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h > index 535f158977b9..8cf350325dc6 100644 > --- a/include/linux/seqlock.h > +++ b/include/linux/seqlock.h > @@ -164,8 +164,6 @@ static inline unsigned read_seqcount_begin(const > seqcount_t *s) > static inline unsigned raw_seqcount_begin(const seqcount_t *s) > { > unsigned ret = ACCESS_ONCE(s->sequence); > - > - seqcount_lockdep_reader_access(s); > smp_rmb(); > return ret & ~1; > }
Just back from vacation, sorry for the slow response. Thanks for submitting this! Also sorry for my confusion mixing raw_seqcount_begin() and raw_seqlock_begin() in our earlier discussion (I blame the hectic vacation prep ;). Acked-by: John Stultz <[email protected]> thanks -john -- 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/
