3.16-stable review patch. If anyone has any objections, please let me know.
------------------
From: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Waiman Long <Waiman.Long@xxxxxx>
Cc: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/CAHQdGtRR6SvEhXiqWo24hoUh9AU9cL82Z8Z-d8-7u951F_d+5g@xxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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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