08 Oct, 2015
11 commits
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doc.2015.10.06a: Documentation updates.
percpu-rwsem.2015.10.06a: Optimization of per-CPU reader-writer semaphores.
torture.2015.10.06a: Torture-test updates. -
exp.2015.10.07a: Reduce OS jitter of RCU-sched expedited grace periods.
fixes.2015.10.06a: Miscellaneous fixes. -
Earlier versions of synchronize_sched_expedited() can prematurely end
grace periods due to the fact that a CPU marked as cpu_is_offline()
can still be using RCU read-side critical sections during the time that
CPU makes its last pass through the scheduler and into the idle loop
and during the time that a given CPU is in the process of coming online.
This commit therefore eliminates this window by adding additional
interaction with the CPU-hotplug operations.Signed-off-by: Paul E. McKenney
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This commit redirects synchronize_rcu_expedited()'s wait to
synchronize_sched_expedited_wait(), thus enabling RCU CPU
stall warnings.Signed-off-by: Paul E. McKenney
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This commit adds task-print ability to the expedited RCU CPU stall
warning messages in preparation for adding stall warnings to
synchornize_rcu_expedited().Signed-off-by: Paul E. McKenney
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This commit makes the RCU CPU stall warning message print online/offline
indications immediately after the CPU number. A "O" indicates global
offline, a "." global online, and a "o" indicates RCU believes that the
CPU is offline for the current grace period and "." otherwise, and an
"N" indicates that RCU believes that the CPU will be offline for the
next grace period, and "." otherwise, all right after the CPU number.
So for CPU 10, you would normally see "10-...:" indicating that everything
believes that the CPU is online.Signed-off-by: Paul E. McKenney
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Now that sync_sched_exp_select_cpus() and sync_rcu_exp_select_cpus()
are identical aside from the the argument to smp_call_function_single(),
this commit consolidates them with a functional argument.Signed-off-by: Paul E. McKenney
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This commit brings sync_sched_exp_select_cpus() into alignment with
sync_rcu_exp_select_cpus(), as a first step towards consolidating them
into one function.Signed-off-by: Paul E. McKenney
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Now that synchronize_sched_expedited() uses IPIs, a hook in
rcu_sched_qs(), and the ->expmask field in the rcu_node combining
tree, it is no longer necessary to exclude CPU hotplug. Any
races with CPU hotplug will be detected when attempting to send
the IPI. This commit therefore removes the code excluding
CPU hotplug operations.Signed-off-by: Paul E. McKenney
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This reverts commit af859beaaba4 (rcu: Silence lockdep false positive
for expedited grace periods). Because synchronize_rcu_expedited()
no longer invokes synchronize_sched_expedited(), ->exp_funnel_mutex
acquisition is no longer nested, so the false positive no longer happens.
This commit therefore removes the extra lockdep data structures, as they
are no longer needed. -
This commit switches synchronize_sched_expedited() from stop_one_cpu_nowait()
to smp_call_function_single(), thus moving from an IPI and a pair of
context switches to an IPI and a single pass through the scheduler.
Of course, if the scheduler actually does decide to switch to a different
task, there will still be a pair of context switches, but there would
likely have been a pair of context switches anyway, just a bit later.Signed-off-by: Paul E. McKenney
07 Oct, 2015
16 commits
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The torturing_tasks() function is used only in kernels built with
CONFIG_PROVE_RCU=y, so the second definition can result in unused-function
compiler warnings. This commit adds __maybe_unused to suppress these
warnings.Signed-off-by: Paul E. McKenney
Reviewed-by: Josh Triplett -
The rcutorture module has a list of torture types, and specifying a
type not on this list is supposed to cleanly fail the module load.
Unfortunately, the "fail" happens without the "cleanly". This commit
therefore adds the needed clean-up after an incorrect torture_type.Reported-by: David Miller
Signed-off-by: Paul E. McKenney
Acked-by: David Miller
Reviewed-by: Josh Triplett -
1. Rename __rcu_sync_is_idle() to rcu_sync_lockdep_assert() and
change it to use rcu_lockdep_assert().2. Change rcu_sync_is_idle() to return rsp->gp_state == GP_IDLE
unconditonally, this way we can remove the same check from
rcu_sync_lockdep_assert() and clearly isolate the debugging
code.Note: rcu_sync_enter()->wait_event(gp_state == GP_PASSED) needs
another CONFIG_PROVE_RCU check, the same as is done in ->sync(); but
this needs some simple preparations in the core RCU code to avoid the
code duplication.Signed-off-by: Oleg Nesterov
Signed-off-by: Paul E. McKenney
Reviewed-by: Josh Triplett -
This commit allows rcu_sync structures to be safely deallocated,
The trick is to add a new ->wait field to the gp_ops array.
This field is a pointer to the rcu_barrier() function corresponding
to the flavor of RCU in question. This allows a new rcu_sync_dtor()
to wait for any outstanding callbacks before freeing the rcu_sync
structure.Signed-off-by: Oleg Nesterov
Signed-off-by: Peter Zijlstra (Intel)
Signed-off-by: Paul E. McKenney
Reviewed-by: Josh Triplett -
This commit validates that the caller of rcu_sync_is_idle() holds the
corresponding type of RCU read-side lock, but only in kernels built
with CONFIG_PROVE_RCU=y. This validation is carried out via a new
rcu_sync_ops->held() method that is checked within rcu_sync_is_idle().Note that although this does add code to the fast path, it only does so
in kernels built with CONFIG_PROVE_RCU=y.Suggested-by: "Paul E. McKenney"
Signed-off-by: Oleg Nesterov
Signed-off-by: Peter Zijlstra (Intel)
Signed-off-by: Paul E. McKenney
Reviewed-by: Josh Triplett -
This commit adds the new struct rcu_sync_ops which holds sync/call
methods, and turns the function pointers in rcu_sync_struct into an array
of struct rcu_sync_ops. This simplifies the "init" helpers by collapsing
a switch statement and explicit multiple definitions into a simple
assignment and a helper macro, respectively.Signed-off-by: Oleg Nesterov
Signed-off-by: Peter Zijlstra (Intel)
Signed-off-by: Paul E. McKenney
Reviewed-by: Josh Triplett -
The rcu_sync infrastructure can be thought of as infrastructure to be
used to implement reader-writer primitives having extremely lightweight
readers during times when there are no writers. The first use is in
the percpu_rwsem used by the VFS subsystem.This infrastructure is functionally equivalent to
struct rcu_sync_struct {
atomic_t counter;
};/* Check possibility of fast-path read-side operations. */
static inline bool rcu_sync_is_idle(struct rcu_sync_struct *rss)
{
return atomic_read(&rss->counter) == 0;
}/* Tell readers to use slowpaths. */
static inline void rcu_sync_enter(struct rcu_sync_struct *rss)
{
atomic_inc(&rss->counter);
synchronize_sched();
}/* Allow readers to once again use fastpaths. */
static inline void rcu_sync_exit(struct rcu_sync_struct *rss)
{
synchronize_sched();
atomic_dec(&rss->counter);
}The main difference is that it records the state and only calls
synchronize_sched() if required. At least some of the calls to
synchronize_sched() will be optimized away when rcu_sync_enter() and
rcu_sync_exit() are invoked repeatedly in quick succession.Signed-off-by: Oleg Nesterov
Signed-off-by: Peter Zijlstra (Intel)
Signed-off-by: Paul E. McKenney
Reviewed-by: Josh Triplett -
This commit moves cond_resched_rcu_qs() into stutter_wait(), saving
a line and also avoiding RCU CPU stall warnings from all torture
loops containing a stutter_wait().Signed-off-by: Paul E. McKenney
Reviewed-by: Josh Triplett -
This commit corrects the comment for the values of the ->gp_state field,
which previously incorrectly said that these were for the ->gp_flags
field.Signed-off-by: Paul E. McKenney
Reviewed-by: Josh Triplett -
Commit commit 4cdfc175c25c89ee ("rcu: Move quiescent-state forcing
into kthread") started the process of folding the old ->fqs_state into
->gp_state, but did not complete it. This situation does not cause
any malfunction, but can result in extremely confusing trace output.
This commit completes this task of eliminating ->fqs_state in favor
of ->gp_state.The old ->fqs_state was also used to decide when to collect dyntick-idle
snapshots. For this purpose, we add a boolean variable into the kthread,
which is set on the first call to rcu_gp_fqs() for a given grace period
and clear otherwise.Signed-off-by: Petr Mladek
Signed-off-by: Paul E. McKenney
Reviewed-by: Josh Triplett -
Currently, __srcu_read_lock() cannot be invoked from restricted
environments because it contains calls to preempt_disable() and
preempt_enable(), both of which can invoke lockdep, which is a bad
idea in some restricted execution modes. This commit therefore moves
the preempt_disable() and preempt_enable() from __srcu_read_lock()
to srcu_read_lock(). It also inserts the preempt_disable() and
preempt_enable() around the call to __srcu_read_lock() in do_exit().Signed-off-by: Paul E. McKenney
Reviewed-by: Josh Triplett -
This commit makes the RCU CPU stall warning message print online/offline
indications immediately after a hyphen following the CPU number. A "O"
indicates that the global CPU-hotplug system believes that the CPU is
online, a "o" that RCU perceived the CPU to be online at the beginning
of the current expedited grace period, and an "N" that RCU currently
believes that it will perceive the CPU as being online at the beginning
of the next expedited grace period, with "." otherwise for all three
indications. So for CPU 10, you would normally see "10-OoN:" indicating
that everything believes that the CPU is online.Signed-off-by: Paul E. McKenney
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This commit loosens rcutree.rcu_fanout_leaf range checks
and replaces a panic() with a fallback to compile-time values.
This fallback is accompanied by a WARN_ON(), and both occur when the
rcutree.rcu_fanout_leaf value is too small to accommodate the number of
CPUs. For example, given the current four-level limit for the rcu_node
tree, a system with more than 16 CPUs built with CONFIG_FANOUT=2 must
have rcutree.rcu_fanout_leaf larger than 2.Reported-by: Peter Zijlstra
Signed-off-by: Paul E. McKenney
Reviewed-by: Josh Triplett -
Because preempt_disable() maps to barrier() for non-debug builds,
it forces the compiler to spill and reload registers. Because Tree
RCU and Tiny RCU now only appear in CONFIG_PREEMPT=n builds, these
barrier() instances generate needless extra code for each instance of
rcu_read_lock() and rcu_read_unlock(). This extra code slows down Tree
RCU and bloats Tiny RCU.This commit therefore removes the preempt_disable() and preempt_enable()
from the non-preemptible implementations of __rcu_read_lock() and
__rcu_read_unlock(), respectively. However, for debug purposes,
preempt_disable() and preempt_enable() are still invoked if
CONFIG_PREEMPT_COUNT=y, because this allows detection of sleeping inside
atomic sections in non-preemptible kernels.However, Tiny and Tree RCU operates by coalescing all RCU read-side
critical sections on a given CPU that lie between successive quiescent
states. It is therefore necessary to compensate for removing barriers
from __rcu_read_lock() and __rcu_read_unlock() by adding them to a
couple of the RCU functions invoked during quiescent states, namely to
rcu_all_qs() and rcu_note_context_switch(). However, note that the latter
is more paranoia than necessity, at least until link-time optimizations
become more aggressive.This is based on an earlier patch by Paul E. McKenney, fixing
a bug encountered in kernels built with CONFIG_PREEMPT=n and
CONFIG_PREEMPT_COUNT=y.Signed-off-by: Boqun Feng
Signed-off-by: Paul E. McKenney -
We have had the call_rcu_func_t typedef for a quite awhile, but we still
use explicit function pointer types in some places. These types can
confuse cscope and can be hard to read. This patch therefore replaces
these types with the call_rcu_func_t typedef.Signed-off-by: Boqun Feng
Signed-off-by: Paul E. McKenney
Reviewed-by: Josh Triplett -
As we now have rcu_callback_t typedefs as the type of rcu callbacks, we
should use it in call_rcu*() and friends as the type of parameters. This
could save us a few lines of code and make it clear which function
requires an rcu callbacks rather than other callbacks as its argument.Besides, this can also help cscope to generate a better database for
code reading.Signed-off-by: Boqun Feng
Signed-off-by: Paul E. McKenney
Reviewed-by: Josh Triplett
21 Sep, 2015
9 commits
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This commit converts the rcu_data structure's ->cpu_no_qs field
to a union. The bytewise side of this union allows individual access
to indications as to whether this CPU needs to find a quiescent state
for a normal (.norm) and/or expedited (.exp) grace period. The setwise
side of the union allows testing whether or not a quiescent state is
needed at all, for either type of grace period.For now, only .norm is used. A later commit will introduce the expedited
usage.Signed-off-by: Paul E. McKenney
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This commit inverts the sense of the rcu_data structure's ->passed_quiesce
field and renames it to ->cpu_no_qs. This will allow a later commit to
use an "aggregate OR" operation to test expedited as well as normal grace
periods without added overhead.Signed-off-by: Paul E. McKenney
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An upcoming commit needs to invert the sense of the ->passed_quiesce
rcu_data structure field, so this commit is taking this opportunity
to clarify things a bit by renaming ->qs_pending to ->core_needs_qs.So if !rdp->core_needs_qs, then this CPU need not concern itself with
quiescent states, in particular, it need not acquire its leaf rcu_node
structure's ->lock to check. Otherwise, it needs to report the next
quiescent state.Signed-off-by: Paul E. McKenney
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Currently, synchronize_sched_expedited() uses a single global counter
to track the number of remaining context switches that the current
expedited grace period must wait on. This is problematic on large
systems, where the resulting memory contention can be pathological.
This commit therefore makes synchronize_sched_expedited() instead use
the combining tree in the same manner as synchronize_rcu_expedited(),
keeping memory contention down to a dull roar.This commit creates a temporary function sync_sched_exp_select_cpus()
that is very similar to sync_rcu_exp_select_cpus(). A later commit
will consolidate these two functions, which becomes possible when
synchronize_sched_expedited() switches from stop_one_cpu_nowait() to
smp_call_function_single().Signed-off-by: Paul E. McKenney
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The current preemptible-RCU expedited grace-period algorithm invokes
synchronize_sched_expedited() to enqueue all tasks currently running
in a preemptible-RCU read-side critical section, then waits for all the
->blkd_tasks lists to drain. This works, but results in both an IPI and
a double context switch even on CPUs that do not happen to be running
in a preemptible RCU read-side critical section.This commit implements a new algorithm that causes less OS jitter.
This new algorithm IPIs all online CPUs that are not idle (from an
RCU perspective), but refrains from self-IPIs. If a CPU receiving
this IPI is not in a preemptible RCU read-side critical section (or
is just now exiting one), it pushes quiescence up the rcu_node tree,
otherwise, it sets a flag that will be handled by the upcoming outermost
rcu_read_unlock(), which will then push quiescence up the tree.The expedited grace period must of course wait on any pre-existing blocked
readers, and newly blocked readers must be queued carefully based on
the state of both the normal and the expedited grace periods. This
new queueing approach also avoids the need to update boost state,
courtesy of the fact that blocked tasks are no longer ever migrated to
the root rcu_node structure.Signed-off-by: Paul E. McKenney
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This commit replaces sync_rcu_preempt_exp_init1(() and
sync_rcu_preempt_exp_init2() with sync_exp_reset_tree_hotplug()
and sync_exp_reset_tree(), which will also be used by
synchronize_sched_expedited(), and sync_rcu_exp_select_nodes(), which
contains code specific to synchronize_rcu_expedited().Signed-off-by: Paul E. McKenney
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This is a nearly pure code-movement commit, moving rcu_report_exp_rnp(),
sync_rcu_preempt_exp_done(), and rcu_preempted_readers_exp() so
that later commits can make synchronize_sched_expedited() use them.
The non-code-movement portion of this commit tags rcu_report_exp_rnp()
as __maybe_unused to avoid build errors when CONFIG_PREEMPT=n.Signed-off-by: Paul E. McKenney
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Now that there is an ->expedited_wq waitqueue in each rcu_state structure,
there is no need for the sync_rcu_preempt_exp_wq global variable. This
commit therefore substitutes ->expedited_wq for sync_rcu_preempt_exp_wq.
It also initializes ->expedited_wq only once at boot instead of at the
start of each expedited grace period.Signed-off-by: Paul E. McKenney
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In kernels built with CONFIG_PREEMPT=y, synchronize_rcu_expedited()
invokes synchronize_sched_expedited() while holding RCU-preempt's
root rcu_node structure's ->exp_funnel_mutex, which is acquired after
the rcu_data structure's ->exp_funnel_mutex. The first thing that
synchronize_sched_expedited() will do is acquire RCU-sched's rcu_data
structure's ->exp_funnel_mutex. There is no danger of an actual deadlock
because the locking order is always from RCU-preempt's expedited mutexes
to those of RCU-sched. Unfortunately, lockdep considers both rcu_data
structures' ->exp_funnel_mutex to be in the same lock class and therefore
reports a deadlock cycle.This commit silences this false positive by placing RCU-sched's rcu_data
structures' ->exp_funnel_mutex locks into their own lock class.Reported-by: Sasha Levin
Signed-off-by: Paul E. McKenney
04 Aug, 2015
4 commits
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RCU is the only thing that uses smp_mb__after_unlock_lock(), and is
likely the only thing that ever will use it, so this commit makes this
macro private to RCU.Signed-off-by: Paul E. McKenney
Cc: Will Deacon
Cc: Peter Zijlstra
Cc: Benjamin Herrenschmidt
Cc: "linux-arch@vger.kernel.org" -
doc.2015.07.15a: Documentation updates.
torture.2015.07.15a: Torture-test updates. -
fixes.2015.07.22a: Miscellaneous fixes.
initexp.2015.08.04a: Initialization and expedited updates.
(Single branch due to conflicts.) -
In a CONFIG_PREEMPT=y kernel, synchronize_rcu_expedited()
acquires the ->exp_funnel_mutex in rcu_preempt_state, then invokes
synchronize_sched_expedited, which acquires the ->exp_funnel_mutex in
rcu_sched_state. There can be no deadlock because rcu_preempt_state
->exp_funnel_mutex acquisition always precedes that of rcu_sched_state.
But lockdep does not know that, so it gives false-positive splats.This commit therefore associates a separate lock_class_key structure
with the rcu_sched_state structure's ->exp_funnel_mutex, allowing
lockdep to see the lock ordering, avoiding the false positives.Signed-off-by: Paul E. McKenney