Because many of RCU's files have not been included into docbook, a
number of errors have accumulated. This commit fixes them.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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>
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>
Commit d160a727c4 ("srcu: Make SRCU be built by default") in response
to build errors, which were caused by code that included srcu.h
despite !SRCU. However, srcutiny.o is almost 2K of code, which is not
insignificant for those attempting to run the Linux kernel on IoT devices.
This commit therefore makes SRCU be once again optional, and adjusts
srcu.h to allow error-free inclusion in !SRCU kernel builds.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Linu Cherian reported a WARN in cleanup_srcu_struct() when shutting
down a guest running iperf on a VFIO assigned device. This happens
because irqfd_wakeup() calls srcu_read_lock(&kvm->irq_srcu) in interrupt
context, while a worker thread does the same inside kvm_set_irq(). If the
interrupt happens while the worker thread is executing __srcu_read_lock(),
updates to the Classic SRCU ->lock_count[] field or the Tree SRCU
->srcu_lock_count[] field can be lost.
The docs say you are not supposed to call srcu_read_lock() and
srcu_read_unlock() from irq context, but KVM interrupt injection happens
from (host) interrupt context and it would be nice if SRCU supported the
use case. KVM is using SRCU here not really for the "sleepable" part,
but rather due to its IPI-free fast detection of grace periods. It is
therefore not desirable to switch back to RCU, which would effectively
revert commit 719d93cd5f ("kvm/irqchip: Speed up KVM_SET_GSI_ROUTING",
2014-01-16).
However, the docs are overly conservative. You can have an SRCU instance
only has users in irq context, and you can mix process and irq context
as long as process context users disable interrupts. In addition,
__srcu_read_unlock() actually uses this_cpu_dec() on both Tree SRCU and
Classic SRCU. For those two implementations, only srcu_read_lock()
is unsafe.
When Classic SRCU's __srcu_read_unlock() was changed to use this_cpu_dec(),
in commit 5a41344a3d ("srcu: Simplify __srcu_read_unlock() via
this_cpu_dec()", 2012-11-29), __srcu_read_lock() did two increments.
Therefore it kept __this_cpu_inc(), with preempt_disable/enable in
the caller. Tree SRCU however only does one increment, so on most
architectures it is more efficient for __srcu_read_lock() to use
this_cpu_inc(), and any performance differences appear to be down in
the noise.
Cc: stable@vger.kernel.org
Fixes: 719d93cd5f ("kvm/irqchip: Speed up KVM_SET_GSI_ROUTING")
Reported-by: Linu Cherian <linuc.decode@gmail.com>
Suggested-by: Linu Cherian <linuc.decode@gmail.com>
Cc: kvm@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The TREE_SRCU rewrite is large and a bit on the non-simple side, so
this commit helps reduce risk by allowing the old v4.11 SRCU algorithm
to be selected using a new CLASSIC_SRCU Kconfig option that depends
on RCU_EXPERT. The default is to use the new TREE_SRCU and TINY_SRCU
algorithms, in order to help get these the testing that they need.
However, if your users do not require the update-side scalability that
is to be provided by TREE_SRCU, select RCU_EXPERT and then CLASSIC_SRCU
to revert back to the old classic SRCU algorithm.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
In response to automated complaints about modifications to SRCU
increasing its size, this commit creates a tiny SRCU that is
used in SMP=n && PREEMPT=n builds.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
SRCU's implementation of expedited grace periods has always assumed
that the SRCU instance is idle when the expedited request arrives.
This commit improves this a bit by maintaining a count of the number
of outstanding expedited requests, thus allowing prior non-expedited
grace periods accommodate these requests by shifting to expedited mode.
However, any non-expedited wait already in progress will still wait for
the full duration.
Improved control of expedited grace periods is planned, but one step
at a time.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Updating ->srcu_state and ->srcu_gp_seq will lead to extremely complex
race conditions given multiple callback queues, so this commit takes
advantage of the two-bit state now available in rcu_seq counters to
store the state in the bottom two bits of ->srcu_gp_seq.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit switches SRCU from custom-built callback queues to the new
rcu_segcblist structure. This change associates grace-period sequence
numbers with groups of callbacks, which will be needed for efficient
processing of per-CPU callbacks.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit adds grace-period sequence numbers, which will be used to
handle mid-boot grace periods and per-CPU callback lists.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The current SRCU grace-period processing might never reach the last
portion of srcu_advance_batches(). This is OK given the current
implementation, as the first portion, up to the try_check_zero()
following the srcu_flip() is sufficient to drive grace periods forward.
However, it has the unfortunate side-effect of making it impossible to
determine when a given grace period has ended, and it will be necessary
to efficiently trace ends of grace periods in order to efficiently handle
per-CPU SRCU callback lists.
This commit therefore adds states to the SRCU grace-period processing,
so that the end of a given SRCU grace period is marked by the transition
to the SRCU_STATE_DONE state.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
SRCU uses two per-cpu counters: a nesting counter to count the number of
active critical sections, and a sequence counter to ensure that the nesting
counters don't change while they are being added together in
srcu_readers_active_idx_check().
This patch instead uses per-cpu lock and unlock counters. Because both
counters only increase and srcu_readers_active_idx_check() reads the unlock
counter before the lock counter, this achieves the same end without having
to increment two different counters in srcu_read_lock(). This also saves a
smp_mb() in srcu_readers_active_idx_check().
Possible bug: There is no guarantee that the lock counter won't overflow
during srcu_readers_active_idx_check(), as there are no memory barriers
around srcu_flip() (see comment in srcu_readers_active_idx_check() for
details). However, this problem was already present before this patch.
Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Lance Roy <ldr709@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
SRCU uses per-CPU variables, and DEFINE_STATIC_SRCU() uses a static
per-CPU variable. However, per-CPU variables have significant
restrictions, for example, names of per-CPU variables must be globally
unique, even if declared static. These restrictions carry over to
DEFINE_STATIC_SRCU(), and this commit therefore documents these
restrictions.
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Suggested-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Tejun Heo <tj@kernel.org>
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 <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
The rcu_dereference_check() family of primitives evaluates the RCU
lockdep expression first, and only then evaluates the expression passed
in. This works fine normally, but can potentially fail in environments
(such as NMI handlers) where lockdep cannot be invoked. The problem is
that even if the expression passed in is "1", the compiler would need to
prove that the RCU lockdep expression (rcu_read_lock_held(), for example)
is free of side effects in order to be able to elide it. Given that
rcu_read_lock_held() is sometimes separately compiled, the compiler cannot
always use this optimization.
This commit therefore reverse the order of evaluation, so that the
expression passed in is evaluated first, and the RCU lockdep expression is
evaluated only if the passed-in expression evaluated to false, courtesy
of the C-language short-circuit boolean evaluation rules. This compells
the compiler to forego executing the RCU lockdep expression in cases
where the passed-in expression evaluates to "1" at compile time, so that
(for example) rcu_dereference_raw() can be guaranteed to execute safely
within an NMI handler.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
The DEFINE_SRCU() and DEFINE_STATIC_SRCU() definitions are quite
similar, so this commit combines them, saving a bit of code and removing
redundancy.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
When rcutorture used only the low-order 32 bits of the grace-period
number, it was not a problem for SRCU to use a 32-bit completed field.
However, rcutorture now uses the full 64 bits on 64-bit systems, so
this commit converts SRCU's ->completed field to unsigned long so as to
provide 64 bits on 64-bit systems.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
All of the RCU source files have the usual GPL header, which contains a
long-obsolete postal address for FSF. To avoid the need to track the
FSF office's movements, this commit substitutes the URL where GPL may
be found.
Reported-by: Greg KH <gregkh@linuxfoundation.org>
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
srcu read lock/unlock include a full memory barrier
but that's an implementation detail.
Add an API for make memory fencing explicit for
users that need this barrier, to make sure we
can change it as needed without breaking all users.
Acked-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
These interfaces never did get used, so this commit removes them,
their rcutorture tests, and documentation referencing them.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
SRCU has its own statemachine and no longer relies on normal RCU.
Its read-side critical section can now be used by an offline CPU, so this
commit removes the check and the comments, reverting the SRCU portion
of ff195cb6 (rcu: Warn when srcu_read_lock() is used in an extended
quiescent state).
It also makes the codes match the comments in whatisRCU.txt:
g. Do you need read-side critical sections that are respected
even though they are in the middle of the idle loop, during
user-mode execution, or on an offlined CPU? If so, SRCU is the
only choice that will work for you.
[ paulmck: There is at least one remaining issue, namely use of lockdep
with tracing enabled. ]
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
SRCU has its own statemachine and no longer relies on normal RCU.
Its read-side critical section can now be used by an offline CPU, so this
commit removes the check and the comments, reverting the SRCU portion
of c0d6d01b (rcu: Check for illegal use of RCU from offlined CPUs).
It also makes the code match the comments in whatisRCU.txt:
g. Do you need read-side critical sections that are respected
even though they are in the middle of the idle loop, during
user-mode execution, or on an offlined CPU? If so, SRCU is the
only choice that will work for you.
[ paulmck: There is at least one remaining issue, namely use of lockdep
with tracing enabled. ]
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
In old days, we had two different API sets for dynamic-allocated per-CPU
data and DEFINE_PER_CPU()-defined per_cpu data, and because SRCU used
dynamic-allocated per-CPU data, its srcu_struct structures cannot be
declared statically. This commit therefore introduces DEFINE_SRCU()
and DEFINE_STATIC_SRCU() to allow statically declared SRCU structures,
using the new static per-CPU interfaces.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Updated for __DELAYED_WORK_INITIALIZER() added argument,
fixed whitespace issue. ]
Because process_srcu() will be used in DEFINE_SRCU(), which is a macro
that could be expanded pretty much anywhere, it can no longer be static.
Note that process_srcu() is still internal to srcu.h.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
