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Subject[PATCH tip/core/rcu 0/9] rcu: v3 add lockdep-based diagnostics to rcu_dereference()

This patch series adds lockdep-based checking to the rcu_dereference()
primitive in order to flag misuses of RCU. The first three patches put
the RCU infrastructure in place, the next five use this infrastructure in
the net, sched, vfs, radix-tree, and idr subsystems, and the last patch
documents how to use the new lockdep-checked rcu_dereference() primitives.

The new (and default-disabled) CONFIG_PROVE_RCU makes this safe to include
in tip/core/rcu -- unlike v2, your system won't complain about RCU misuse
unless you ask it to. There are still several situations that trigger
on systems I have access to (and I have email out on a couple of them),
some of the remaining will be triggered only by hardware I don't have
access to and kernel features I am unfamiliar with. So this is ready
for some more-general testing.

Changes since v2 (

o Removed references to the check condition for the non-lockdep
version of rcu_dereference_check(), thus preventing numerous
build errors.

o Create a CONFIG_PROVE_RCU (default disabled) so that developers
who want to use lockdep only to debug locks aren't bothered
by RCU-specific lockdep complaints that will no doubt persist
for a little bit while some of the more obscure uses of RCU
are reverse-engineered.

o Fix a few more issues identified by the checking.

o Add documentation in Documentation/RCU/lockdep.txt.

Changes since v1 (

o Made SRCU have per-srcu_struct lockdep maps to prevent lockdep
from conflating independent uses of SRCU, and updated the
rcu_dereference() checking in rcutorture to match.

o Fix a few issues identified by the checking.

o Disable checking within RCU list macros, RCU radix trees, and

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