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Subject[PATCH tip/core/rcu 0/21] v6 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 four patches put
the RCU infrastructure in place, the next eight use this infrastructure
in the net, sched, vfs, radix-tree, idr, and security subsystems, and
patch 13 documents how to use the new lockdep-checked rcu_dereference()
primitives. The remaining eight patches are other changes that also need
to be applied, including some relatively urgent RCU_STALL patches.

The new (and default-disabled) CONFIG_PROVE_RCU makes this safe to
include in tip/core/rcu -- unlike v2 and earlier, 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 much wider testing.

Changes since v5 (

o Fix a deadlock located by Thomas Gleixner that affects
TREE_PREEMPT_RCU in some CPU-stall detection scenarios.

o Add Dan Carpenter's cleanup to a mod_timer() in rcutorture.

o Add a RCU_CPU_STALL_VERBOSE to enable dumping more information
on tasks stalling the current RCU grace period.

o Applied Acked-by lines that people have sent (thank you all!).

Changes since v4 (

o Apply review comments from Peter Ziljstra.

o Another documentation update.

o Fixes that avoid overflowing signed integers.

o Rebased Thomas Gleixner's raw-spinlock patch on this series.
(Thomas's original at

Changes since v3 (

o Fix a few more issues identified by the checking.

o Add a documentation update.

o Accelerate RCU grace periods when the current CPU is the last
non-dyntick-idle CPU in the system, which is important for
some multi-core battery-powered devices.

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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