Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 3.14 175/238] lockdep: Revert lockdep check in raw_seqcount_begin() | Date | Fri, 3 Oct 2014 14:31:30 -0700 |
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3.14-stable review patch. If anyone has any objections, please let me know.
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From: Trond Myklebust <trond.myklebust@primarydata.com>
commit 22fdcf02f6e80d64a927f702dd9d631a927d87d4 upstream.
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 Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: John Stultz <john.stultz@linaro.org> Cc: "David S. Miller" <davem@davemloft.net> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Waiman Long <Waiman.Long@hp.com> Cc: Stephen Boyd <sboyd@codeaurora.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/CAHQdGtRR6SvEhXiqWo24hoUh9AU9cL82Z8Z-d8-7u951F_d+5g@mail.gmail.com Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- include/linux/seqlock.h | 2 -- 1 file changed, 2 deletions(-)
--- a/include/linux/seqlock.h +++ b/include/linux/seqlock.h @@ -164,8 +164,6 @@ static inline unsigned read_seqcount_beg 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; }
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