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commit 28585a832602747cbfa88ad8934013177a3aae38 upstream.
A number of architecture invoke rcu_irq_enter() on exception entry in
order to allow RCU read-side critical sections in the exception handler
when the exception is from an idle or nohz_full CPU. This works, at
least unless the exception happens in an NMI handler. In that case,
rcu_nmi_enter() would already have exited the extended quiescent state,
which would mean that rcu_irq_enter() would (incorrectly) cause RCU
to think that it is again in an extended quiescent state. This will
in turn result in lockdep splats in response to later RCU read-side
critical sections.
This commit therefore causes rcu_irq_enter() and rcu_irq_exit() to
take no action if there is an rcu_nmi_enter() in effect, thus avoiding
the unscheduled return to RCU quiescent state. This in turn should
make the kernel safe for on-demand RCU voyeurism.
Link: http://lkml.kernel.org/r/20170922211022.GA18084@linux.vnet.ibm.com
Fixes: 0be964be0 ("module: Sanitize RCU usage and locking")
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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commit 35732cf9dd38b1efb0f2f22c91c61b51337d1ac3 upstream.
Tree RCU guarantees that every online CPU has a memory barrier between
any given grace period and any of that CPU's RCU read-side sections that
must be ordered against that grace period. Since RCU doesn't always
know where read-side critical sections are, the actual implementation
guarantees order against prior and subsequent non-idle non-offline code,
whether in an RCU read-side critical section or not. As a result, there
does not need to be a memory barrier at the end of synchronize_rcu()
and friends because the ordering internal to the grace period has
ordered every CPU's post-grace-period execution against each CPU's
pre-grace-period execution, again for all non-idle online CPUs.
In contrast, SRCU can have non-idle online CPUs that are completely
uninvolved in a given SRCU grace period, for example, a CPU that
never runs any SRCU read-side critical sections and took no part in
the grace-period processing. It is in theory possible for a given
synchronize_srcu()'s wakeup to be delivered to a CPU that was completely
uninvolved in the prior SRCU grace period, which could mean that the
code following that synchronize_srcu() would end up being unordered with
respect to both the grace period and any pre-existing SRCU read-side
critical sections.
This commit therefore adds an smp_mb() to the end of __synchronize_srcu(),
which prevents this scenario from occurring.
Reported-by: Lance Roy <ldr709@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Lance Roy <ldr709@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Tiny RCU's job is to be tiny, so this commit removes its RCU CPU
stall warning code. After this, there is no longer any need for
rcu_sched_ctrlblk and rcu_bh_ctrlblk to be in tiny_plugin.h, so this
commit also moves them to tiny.c.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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This commit saves a few lines by getting rid of Tiny RCU's event tracing.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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RCU's debugging Kconfig options are in the unintuitive location
lib/Kconfig.debug, and there are enough of them that it would be good for
them to be more centralized. This commit therefore extracts RCU's Kconfig
options from init/Kconfig into a new kernel/rcu/Kconfig.debug file.
Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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RCU's Kconfig options are scattered, and there are enough of them
that it would be good for them to be more centralized. This commit
therefore extracts RCU's Kconfig options from init/Kconfig into a new
kernel/rcu/Kconfig file.
Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The CONFIG_RCU_NOCB_CPU_ALL, CONFIG_RCU_NOCB_CPU_NONE, and
CONFIG_RCU_NOCB_CPU_ZERO Kconfig options are used only in testing and
are redundant with the rcu_nocbs= boot parameter. This commit therefore
removes these three Kconfig options and adjusts the rcutorture scripts
to use the boot parameter instead.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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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>
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Classic SRCU was only ever intended to be a fallback in case of issues
with Tree/Tiny SRCU, and the latter two are doing quite well in testing.
This commit therefore removes Classic SRCU.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The function srcutorture_get_gp_data() duplicated the check for
sp->batch_check0.head instead of also checking sp->batch_check1.head.
The only effect of this typo would be for rcutorture statistics to
understate the fraction of time that an SRCU grace period was in flight,
and only for Classic SRCU. This commit fixes this typo.
Reported-by: David Binderman <dcb314@hotmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The PROVE_RCU_REPEATEDLY Kconfig option was initially added due to
the volume of messages from PROVE_RCU: Doing just one per boot would
have required excessive numbers of boots to locate them all. However,
PROVE_RCU messages are now relatively rare, so there is no longer any
reason to need more than one such message per boot. This commit therefore
removes the PROVE_RCU_REPEATEDLY Kconfig option.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
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Because raw_spin_lock_irqsave() and raw_spin_unlock_irqrestore()
both do typecheck() on their flags argument, there is no point in
duplicating this check in raw_spin_lock_irqsave_rcu_node() and
raw_spin_unlock_irqrestore_rcu_node(). This commit therefore saves
a few lines by removing this duplicated check.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The NO_HZ_FULL_SYSIDLE full-system-idle capability was added in 2013
by commit 0edd1b1784cb ("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>
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Anything that can be done with the RCU_KTHREAD_PRIO Kconfig option can
also be done with the rcutree.kthread_prio kernel boot parameter.
This commit therefore removes this Kconfig option.
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
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The RCU_TORTURE_TEST_SLOW_PREINIT, RCU_TORTURE_TEST_SLOW_PREINIT_DELAY,
RCU_TORTURE_TEST_SLOW_PREINIT_DELAY, RCU_TORTURE_TEST_SLOW_INIT,
RCU_TORTURE_TEST_SLOW_INIT_DELAY, RCU_TORTURE_TEST_SLOW_CLEANUP,
and RCU_TORTURE_TEST_SLOW_CLEANUP_DELAY Kconfig options are only
useful for torture testing, and there are the rcutree.gp_cleanup_delay,
rcutree.gp_init_delay, and rcutree.gp_preinit_delay kernel boot parameters
that rcutorture can use instead. The effect of these parameters is to
artificially slow down grace period initialization and cleanup in order
to make some types of race conditions happen more often.
This commit therefore simplifies Tree RCU a bit by removing the Kconfig
options and adding the corresponding kernel parameters to rcutorture's
.boot files instead. However, this commit also leaves out the kernel
parameters for TREE02, TREE04, and TREE07 in order to have about the
same number of tests slowed as not slowed. TREE01, TREE03, TREE05,
and TREE06 are slowed, and the rest are not slowed.
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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This commit uses TREE RCU's rnp->lock wrappers to replace a few explicit
memory barriers. This change also has the advantage of making SRCU's
memory-ordering properties be implemented in roughly the same way as they
are in Tree RCU.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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This commit moves the now-generic rnp->lock wrapper macros from
kernel/rcu/tree.h to kernel/rcu/rcu.h, thus allowing SRCU to use them.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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Use of smp_mb__after_unlock_lock() would allow SRCU to omit a full
memory barrier during callback execution, so this commit converts
raw_spin_lock_rcu_node() from inline functions to type-generic macros
to allow them to handle locks in srcu_node structures as well as
rcu_node structures.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The rcu_segcblist structure provides quite a bit of functionality, and
Tiny SRCU needs almost none of it. So this commit replaces Tiny SRCU's
uses of rcu_segcblist with a simple singly linked list with tail pointer.
This change significantly reduces Tiny SRCU's memory footprint, more
than making up for the growth caused by the creation of rcu_segcblist.c
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The call_srcu() docbook entry is currently in include/linux/srcu.h,
which causes needless processing for each include point. This commit
therefore moves this entry to kernel/rcu/srcutree.c, which the compiler
reads only once. In addition, the srcu_batches_completed() function is
used only within RCU and its torture-test suites. This commit therefore
also moves this function's declaration from include/linux/srcutiny.h,
include/linux/srcutree.h, and include/linux/srcuclassic.h to
kernel/rcu/rcu.h.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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If a given CPU never happens to ever start an SRCU grace period, the
grace-period sequence counter might wrap. If this CPU were to decide to
finally start a grace period, the state of its sdp->srcu_gp_seq_needed
might make it appear that it has already requested this grace period,
which would prevent starting the grace period. If no other CPU ever started
a grace period again, this would look like a grace-period hang. Even
if some other CPU took pity and started the needed grace period, the
leaf rcu_node structure's ->srcu_data_have_cbs field won't have record
of the fact that this CPU has a callback pending, which would look like
a very localized grace-period hang.
This might seem very unlikely, but SRCU grace periods can take less than
a microsecond on small systems, which means that overflow can happen
in much less than an hour on a 32-bit embedded system. And embedded
systems are especially likely to have long-term idle CPUs. Therefore,
it makes sense to prevent this scenario from happening.
This commit therefore scans each srcu_data structure occasionally,
with frequency controlled by the srcutree.counter_wrap_check kernel
boot parameter. This parameter can be set to something like 255
in order to exercise the counter-wrap-prevention code.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The rcu_request_urgent_qs_task() function is used only within RCU,
so there is no point in exporting it to the rest of the kernel from
nclude/linux/rcutiny.h and include/linux/rcutree.h. This commit therefore
moves this function to kernel/rcu/rcu.h.
Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The various functions similar to rcu_batches_started(), the
function show_rcu_gp_kthreads(), the various functions similar to
rcu_force_quiescent_state(), and the variables rcutorture_testseq and
rcutorture_vernum are used only within RCU. There is therefore no point
in exporting them to the kernel at large from include/linux/rcutiny.h
and include/linux/rcutree.h. This commit therefore moves all of these
to kernel/rcu/rcu.h.
Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The rcu_ftrace_dump() function is used only internally to RCU. This
commit therefore moves its declaration from include/linux/rcupdate.h
to kernel/rcu/rcu.h.
Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The rcu_is_nocb_cpu() function is used only internally to RCU. This
commit therefore moves its declaration from include/linux/rcupdate.h
to kernel/rcu/rcu.h.
Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The "__call_rcu(): Leaked duplicate callback" error message from
__call_rcu() has proven to be unhelpful. This commit therefore changes
it to "__call_rcu(): Double-freed CB" and adds the value of the pointer
passed in. The value of the pointer improves debuggability by allowing
correlation with tracing output, for example, the rcu:rcu_callback trace
event.
Reported-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The RCU_SCHEDULER_INACTIVE, RCU_SCHEDULER_INIT, and RCU_SCHEDULER_RUNNING
definitions are used only within RCU, so this commit moves them from
include/linux/rcupdate.h to kernel/rcu/rcu.h.
Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The __rcu_is_watching() function is currently not used, aside from
to implement the rcu_is_watching() function. This commit therefore
eliminates __rcu_is_watching(), which has the beneficial side-effect
of shrinking include/linux/rcupdate.h a bit.
Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The include/linux/rcupdate.h file contains a number of definitions that
are used only to communicate between rcutorture, rcuperf, and the RCU code
itself. There is no point in having these definitions exposed globally
throughout the kernel, so this commit moves them to kernel/rcu/rcu.h.
This change has the added benefit of shrinking rcupdate.h.
Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The rcu_gp_is_normal(), rcu_gp_is_expedited(), rcu_expedite_gp(), and
rcu_unexpedite_gp() functions are intended only for use within the
RCU implementation itself -- the sysfs access is what should be used
outside of RCU. This commit therefore moves the declarations for
these functions to kernel/rcu/rcu.h, and also includes this file into
kernel/rcu/rcutorture.c and kernel/rcu/rcuperf.c. This also has the
beneficial effect of shrinking rcupdate.c a bit.
Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The rcu_expedited and rcu_normal variables are used only by sysctl
and kernel/rcu/update.c, so it does not make sense to their extern
declarations in rcupdate.h. This commit therefore moves these
extern declarations to update.c.
Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The include/linux/rcupdate.h file is included by more than 200
files, so shrinking it should provide some build-time benefits.
This commit therefore moves several docbook comments from rcupdate.h to
kernel/rcu/update.c, kernel/rcu/tree.c, and kernel/rcu/tree_plugin.h, thus
reducing the number of times that the compiler has to scan these comments.
This likely provides only a small benefit, but every little bit helps.
This commit also fixes a malformed bulleted list noted by the 0day
Test Robot.
Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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Wait/wakeup operations do not guarantee ordering on their own. Instead,
either locking or memory barriers are required. This commit therefore
adds memory barriers to wake_nocb_leader() and nocb_leader_wait().
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Krister Johansen <kjlx@templeofstupid.com>
Cc: <stable@vger.kernel.org> # 4.6.x
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The RCU_NOGP_WAKE_NOT, RCU_NOGP_WAKE, and RCU_NOGP_WAKE_FORCE flags
are used to mediate wakeups for the no-CBs CPU kthreads. The "NOGP"
really doesn't make any sense, so this commit does s/NOGP/NOCB/.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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Currently, doing synchronize_rcu_mult(call_rcu, call_rcu) might
(or might not) wait for two RCU grace periods. One approach is
of course "don't do that!", but in CONFIG_PREEMPT=n kernels,
synchronize_rcu_mult(call_rcu, call_rcu_sched) does exactly that.
This results in an ugly #ifdef in sched_cpu_deactivate().
This commit therefore makes __wait_rcu_gp() check for duplicates,
which in turn allows duplicates to be passed to synchronize_rcu_mult()
without risk of waiting twice on the same type of grace period.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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This commit adds DEBUG_OBJECTS_RCU_HEAD checking to detect call_srcu()
counterparts to double-free bugs.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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In Tiny SRCU, __srcu_read_lock() is a trivial function, outweighed by
its EXPORT_SYMBOL_GPL(), and on many architectures, its call sequence.
This commit therefore moves it to srcutiny.h so that it can be inlined.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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Comments can be helpful, but assertions carry more force. This commit
therefore adds lockdep_assert_held() and RCU_LOCKDEP_WARN() calls to
enforce lock-held and interrupt-disabled preconditions.
Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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Comments can be helpful, but assertions carry more force. This
commit therefore adds lockdep_assert_held() and RCU_LOCKDEP_WARN()
calls to enforce lock-held and interrupt-disabled preconditions.
Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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This commit makes srcu_bootup_announce() check for non-default values
of the auto-expedite holdoff time exp_holdoff and print a message if so.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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Because exp_holdoff is not used outside of srcutree.c, it can be static.
This commit therefore makes this change.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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This commit updates rcu_bootup_announce_oddness() to check additional
Kconfig options and module/boot parameters.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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This commit adds a rcupdate_announce_bootup_oddness() function to
print out non-default values of significant kernel boot parameter
settings to aid in debugging.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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This commit adds WARN_ON_ONCE() calls that trigger if either
rcu_sched_qs() or rcu_bh_qs() are invoked with preemption enabled.
In the immortal words of Peter Zijlstra: "these are much harder to ignore
than comments".
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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This commit adds a writer_holdoff boot parameter to rcuperf, which is
intended to be used to test Tree SRCU's auto-expediting. This
boot parameter is in microseconds, and defaults to zero (that is,
disabled). Set it to a bit larger than srcutree.exp_holdoff,
keeping the nanosecond/microsecond conversion, to force Tree SRCU
to auto-expedite more aggressively.
This commit also adds documentation for this parameter, and fixes some
alphabetization while in the neighborhood.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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Common-case use of rcuperf must set rcuperf.nreaders=0 and if not built
as a module, rcuperf.shutdown. This commit therefore sets the default
for rcuperf.nreaders to zero and sets the default for rcuperf.shutdown
to zero if rcuperf is built as a module and to one otherwise.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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This commit rearranges Tiny SRCU's srcu_struct structure, substitutes
u8 for bool, and shrinks counters down to short.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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Currently, the only way to tell whether a given kernel is running
Classic, Tiny, or Tree SRCU is to look at the .config file, which
can easily be lost or associated with the wrong kernel. This commit
therefore has Classic and Tree SRCU identify themselves at boot time.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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This commit adds a perf_type of "srcud", which species that rcuperf
test SRCU on a dynamically initialized srcu_struct.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The sync_rcu_preempt_exp_done() function returns a logical expression,
but its return type is nevertheless int. This commit therefore changes
the return type to bool.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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Paul E. McKenney