It came to my attention that the file "whatisRCU.txt" does not
manage to actually ever spell out what is RCU.
This might not be an issue for a lot of people, but we have to
assume the consumers of these documents are starting from ground
zero; otherwise they'd not be reading the docs.
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Nicholas Piggin <npiggin@gmail.com>
This commit keeps only the historical and low-level discussion of
smp_read_barrier_depends().
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Adjusted to allow for David Howells feedback on prior commit. ]
Now that cond_resched() also provides RCU quiescent states when
needed, it can be used in place of cond_resched_rcu_qs(). This
commit therefore documents this change.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Pull RCU updates from Ingo Molnar:
"The main changes in this cycle are:
- Documentation updates
- RCU CPU stall-warning updates
- Torture-test updates
- Miscellaneous fixes
Size wise the biggest updates are to documentation. Excluding
documentation most of the code increase comes from a single commit
which expands debugging"
* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (24 commits)
srcu: Add parameters to SRCU docbook comments
doc: Rewrite confusing statement about memory barriers
memory-barriers.txt: Fix typo in pairing example
rcu/segcblist: Include rcupdate.h
rcu: Add extended-quiescent-state testing advice
rcu: Suppress lockdep false-positive ->boost_mtx complaints
rcu: Do not include rtmutex_common.h unconditionally
torture: Provide TMPDIR environment variable to specify tmpdir
rcutorture: Dump writer stack if stalled
rcutorture: Add interrupt-disable capability to stall-warning tests
rcu: Suppress RCU CPU stall warnings while dumping trace
rcu: Turn off tracing before dumping trace
rcu: Make RCU CPU stall warnings check for irq-disabled CPUs
sched,rcu: Make cond_resched() provide RCU quiescent state
sched: Make resched_cpu() unconditional
irq_work: Map irq_work_on_queue() to irq_work_on() in !SMP
rcu: Create call_rcu_tasks() kthread at boot time
rcu: Fix up pending cbs check in rcu_prepare_for_idle
memory-barriers: Rework multicopy-atomicity section
memory-barriers: Replace uses of "transitive"
...
The RCU CPU stall warnings have morphed significantly since the last
update, so this commit brings the documentation up to date.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
If a fast system has a worst-case grace-period duration of (say) ten
seconds, then running the same workload on a system ten times as slow
will get you an RCU CPU stall warning given default stall-warning
timeout settings. This commit therefore adds this possibility to
stallwarn.txt.
Reported-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
If a periodic interrupt's handler takes longer to execute than the period
between successive interrupts, RCU's kthreads and softirq handlers can
be prevented from executing, resulting in otherwise inexplicable RCU
CPU stall warnings. This commit therefore calls out this possibility
in Documentation/RCU/stallwarn.txt.
Reported-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit documents the situations in which RCU needs the
scheduling-clock interrupt to be enabled, along with the consequences
of failing to meet RCU's needs in this area.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
There are too many ways for the compiler to optimize (that is, break)
dependencies carried via integer values, so it is now permissible to
carry dependencies only via pointers. This commit catches up some of
the documentation on this point.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
RCU's debugfs tracing used to be the only reasonable low-level debug
information available, but ftrace and event tracing has since surpassed
the RCU debugfs level of usefulness. This commit therefore removes
RCU's debugfs tracing.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The sparse-based checking for non-RCU accesses to RCU-protected pointers
has been around for a very long time, and it is now the only type of
sparse-based checking that is optional. This commit therefore makes
it unconditional.
Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>
The NO_HZ_FULL_SYSIDLE full-system-idle capability was added in 2013
by commit 0edd1b1784 ("nohz_full: Add full-system-idle state machine"),
but has not been used. This commit therefore removes it.
If it turns out to be needed later, this commit can always be reverted.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit classifies tail recursion as an alternative way to write
a loop, with similar limitations.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit documents the auto-expediting requirement satisfied by
commits 2da4b2a7fd ("srcu: Expedite first synchronize_srcu() when idle")
and 22607d66bb ("srcu: Specify auto-expedite holdoff time").
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
A group of Linux kernel hackers reported chasing a bug that resulted
from their assumption that SLAB_DESTROY_BY_RCU provided an existence
guarantee, that is, that no block from such a slab would be reallocated
during an RCU read-side critical section. Of course, that is not the
case. Instead, SLAB_DESTROY_BY_RCU only prevents freeing of an entire
slab of blocks.
However, there is a phrase for this, namely "type safety". This commit
therefore renames SLAB_DESTROY_BY_RCU to SLAB_TYPESAFE_BY_RCU in order
to avoid future instances of this sort of confusion.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: <linux-mm@kvack.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
[ paulmck: Add comments mentioning the old name, as requested by Eric
Dumazet, in order to help people familiar with the old name find
the new one. ]
Acked-by: David Rientjes <rientjes@google.com>
The rcu_all_qs() and rcu_note_context_switch() do a series of checks,
taking various actions to supply RCU with quiescent states, depending
on the outcomes of the various checks. This is a bit much for scheduling
fastpaths, so this commit creates a separate ->rcu_urgent_qs field in
the rcu_dynticks structure that acts as a global guard for these checks.
Thus, in the common case, rcu_all_qs() and rcu_note_context_switch()
check the ->rcu_urgent_qs field, find it false, and simply return.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
The rcu_momentary_dyntick_idle() function scans the RCU flavors, checking
that one of them still needs a quiescent state before doing an expensive
atomic operation on the ->dynticks counter. However, this check reduces
overhead only after a rare race condition, and increases complexity. This
commit therefore removes the scan and the mechanism enabling the scan.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The rcu_qs_ctr variable is yet another isolated per-CPU variable,
so this commit pulls it into the pre-existing rcu_dynticks per-CPU
structure.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The rcu_sched_qs_mask variable is yet another isolated per-CPU variable,
so this commit pulls it into the pre-existing rcu_dynticks per-CPU
structure.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
