Messages in this thread Patch in this message | | | From | Trond Myklebust <> | Subject | [PATCH] Revert lockdep check in raw_seqcount_begin | Date | Thu, 5 Jun 2014 11:31:01 -0400 |
| |
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 <john.stultz@linaro.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: "David S. Miller" <davem@davemloft.net> Cc: Al Viro <viro@zeniv.linux.org.uk> Link: http://lkml.kernel.org/r/CAHQdGtRR6SvEhXiqWo24hoUh9AU9cL82Z8Z-d8-7u951F_d+5g@mail.gmail.com Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com> --- 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; } -- 1.9.3
| |