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git://git.kernel.org/pub/scm/linux/kernel/git/danielt/linux
Pull kgdb updates from Daniel Thompson:
"This was a extremely quiet cycle for kgdb. This consists of two
patches that between them address spelling errors and a switch
fallthrough warning"
* tag 'kgdb-5.14-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/danielt/linux:
kgdb: Fix fall-through warning for Clang
kgdb: Fix spelling mistakes
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In preparation to enable -Wimplicit-fallthrough for Clang, fix a
fall-through warning by explicitly adding a goto statement instead
of letting the code fall through to the next case.
Link: https://github.com/KSPP/linux/issues/115
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20210528200222.GA39201@embeddedor
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
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Fix some spelling mistakes in comments:
initalization ==> initialization
detatch ==> detach
represntation ==> representation
hexidecimal ==> hexadecimal
delimeter ==> delimiter
architecure ==> architecture
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Link: https://lore.kernel.org/r/20210529110305.9446-3-thunder.leizhen@huawei.com
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
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git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu
Pull RCU updates from Paul McKenney:
- Bitmap parsing support for "all" as an alias for all bits
- Documentation updates
- Miscellaneous fixes, including some that overlap into mm and lockdep
- kvfree_rcu() updates
- mem_dump_obj() updates, with acks from one of the slab-allocator
maintainers
- RCU NOCB CPU updates, including limited deoffloading
- SRCU updates
- Tasks-RCU updates
- Torture-test updates
* 'core-rcu-2021.07.04' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (78 commits)
tasks-rcu: Make show_rcu_tasks_gp_kthreads() be static inline
rcu-tasks: Make ksoftirqd provide RCU Tasks quiescent states
rcu: Add missing __releases() annotation
rcu: Remove obsolete rcu_read_unlock() deadlock commentary
rcu: Improve comments describing RCU read-side critical sections
rcu: Create an unrcu_pointer() to remove __rcu from a pointer
srcu: Early test SRCU polling start
rcu: Fix various typos in comments
rcu/nocb: Unify timers
rcu/nocb: Prepare for fine-grained deferred wakeup
rcu/nocb: Only cancel nocb timer if not polling
rcu/nocb: Delete bypass_timer upon nocb_gp wakeup
rcu/nocb: Cancel nocb_timer upon nocb_gp wakeup
rcu/nocb: Allow de-offloading rdp leader
rcu/nocb: Directly call __wake_nocb_gp() from bypass timer
rcu: Don't penalize priority boosting when there is nothing to boost
rcu: Point to documentation of ordering guarantees
rcu: Make rcu_gp_cleanup() be noinline for tracing
rcu: Restrict RCU_STRICT_GRACE_PERIOD to at most four CPUs
rcu: Make show_rcu_gp_kthreads() dump rcu_node structures blocking GP
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'fixes.2021.05.13a', 'kvfree_rcu.2021.05.10c', 'mmdumpobj.2021.05.10c', 'nocb.2021.05.12a', 'srcu.2021.05.12a', 'tasks.2021.05.18a' and 'torture.2021.05.10c' into HEAD
bitmaprange.2021.05.10c: Allow "all" for bitmap ranges.
doc.2021.05.10c: Documentation updates.
fixes.2021.05.13a: Miscellaneous fixes.
kvfree_rcu.2021.05.10c: kvfree_rcu() updates.
mmdumpobj.2021.05.10c: mem_dump_obj() updates.
nocb.2021.05.12a: RCU NOCB CPU updates, including limited deoffloading.
srcu.2021.05.12a: SRCU updates.
tasks.2021.05.18a: Tasks-RCU updates.
torture.2021.05.10c: Torture-test updates.
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RCU priority boosting cannot do anything unless there is at least one
task blocking the current RCU grace period that was preempted within
the RCU read-side critical section that it still resides in. However,
the current rcu_torture_boost_failed() code will count this as an RCU
priority-boosting failure if there were no CPUs blocking the current
grace period. This situation can happen (for example) if the last CPU
blocking the current grace period was subjected to vCPU preemption,
which is always a risk for rcutorture guest OSes.
This commit therefore causes rcu_torture_boost_failed() to refrain from
reporting failure unless there is at least one task blocking the current
RCU grace period that was preempted within the RCU read-side critical
section that it still resides in.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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To make the purpose of the code more apparent, this commit moves the
tests of mem_dump_obj() to a new rcu_torture_mem_dump_obj() function
and calls it from rcu_torture_cleanup().
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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It will frequently be the case that rcu_torture_boost() will get a
->start_gp_poll() cookie that needs almost all of the current grace period
plus an additional grace period to elapse before ->poll_gp_state() will
return true. It is quite possible that the current grace period will have
(say) two seconds of stall by a CPU failing to pass through a quiescent
state, followed by 300 milliseconds of delay due to a preempted reader.
The next grace period might suffer only one second of stall by a CPU,
followed by another 300 milliseconds of delay due to a preempted reader.
This is an example of RCU priority boosting doing its job, but the full
elapsed time of 3.6 seconds exceeds the 3.5-second limit. In addition,
there is no CPU stall in force at the 3.5-second mark, so this would
nevertheless currently be counted as an RCU priority boosting failure.
This commit therefore avoids this sort of false positive by resetting
the gp_state_time timestamp any time that the current grace period is
being blocked by a CPU. This results in extremely frequent calls to
the ->check_boost_failed() function, so this commit provides a lockless
fastpath that is selected by supplying a NULL CPU-number pointer.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Currently, rcu_torture_boost() runs CPU-bound at real-time priority
to force RCU priority inversions. It then checks that grace periods
progress during this CPU-bound time. If grace periods fail to progress,
it reports and RCU priority boosting failure.
However, it is possible (and sometimes does happen) that the grace period
fails to progress due to a CPU failing to pass through a quiescent state
for an extended time period (3.5 seconds by default). This can happen
due to vCPU preemption, long-running interrupts, and much else besides.
There is nothing that RCU priority boosting can do about these situations,
and so they should not be counted as RCU priority boosting failures.
This commit therefore checks for CPUs (as opposed to preempted tasks)
holding up a grace period, and flags the resulting RCU priority boosting
failures, but does not splat nor count them as errors. It does rate-limit
them to avoid flooding the console log.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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It is possible that a delayed grace period that rcu_torture_boost()
was polling for ended while rcu_torture_boost_failed() was printing the
failure splat. It would be good to know when this happens. This commit
therefore has rcu_torture_boost_failed() recheck the grace period after
printing the splat, and printing a message indicating whether or not
the grace period has ended.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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This commit consolidates two loops in rcu_torture_boost(), one of which
counts the number of boost-test episodes and the other of which computes
the start time of the next episode, into one loop that does both with but
a single acquisition of boost_mutex. This means that the count of the
number of boost-test episodes is incremented after an episode completes
rather than before it starts, but it also avoids the over-counting that
was possible previously.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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If an rcu_torture_boost() kthread determines that its grace period
has not yet ended, it invokes rcu_torture_boost_failed() which checks
whether enough time has elapsed for this to be considered a failure of
RCU priority boosting, and, if so, flags the error.
Unfortunately, that kthread might be preempted for some seconds between
the time that it checks the grace period and the time that it checks the
time. This delay can result in a false positive, featuring a complaint
that a particular grace period has not ended, followed by a diagnostic
dump featuring a much later grace period.
This commit avoids these false positives by rechecking for the end of
the grace period after the time check.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Currently, rcutorture's testing of RCU priority boosting insists not
only that grace periods complete, but also that callbacks be invoked.
Although this is in fact what the user would want, ensuring that there
is sufficient CPU bandwidth devoted to callback execution is in fact
the user's responsibility. One could argue that rcutorture can take on
that responsibility, which is true in theory. But in practice, ensuring
sufficient CPU bandwidth to ksoftirqd, any rcuc kthreads, and any rcuo
kthreads is not particularly consistent with rcutorture's main job,
that of stress-testing RCU. In addition, if the system administrator
(say) makes very poor choices when pinning rcuo kthreads and then runs
rcutorture, there really isn't much rcutorture can do.
Besides, RCU priority boosting only boosts lagging readers, not all the
machinery required to invoke callbacks in a timely fashion.
This commit therefore switches rcutorture's evaluation of RCU priority
boosting from callback execution to grace-period completion by using
the new start_poll_synchronize_rcu() and poll_state_synchronize_rcu()
functions. When rcutorture is built in (as in when there is no innocent
workload to inconvenience), the ksoftirqd ktheads are boosted to real-time
priority 2 in order to allow timeouts to work properly in the face of
rcutorture's testing of RCU priority boosting.
Indeed, it is not as easy as it looks to create a reliable test of RCU
priority boosting without destroying the rest of the kernel!
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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This commit adds a (*readlock_held)() function pointer to the
rcu_torture_ops structure in order to make the rcu_torture_one_read()
function's rcu_dereference_check() lockdep expression more appropriate
for a given run.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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This commit adds scale_type of acqrel, lock, and lock-irq to
test acquisition and release. Note that the refscale.nreaders=1
module parameter is required if you wish to test uncontended locking.
In contrast, acqrel uses a per-CPU variable, so should be just fine with
large values of the refscale.nreaders=1 module parameter.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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In some architectures, the no-op variant of show_rcu_tasks_gp_kthreads()
get "no previous prototype" compiler warnings. These are false positives
given that kernel/rcu/tasks.h is included only once. But why put up
with the compiler noise?
This commit therefore adds "static inline" to this definition to force
the compiler to accept this situation, while also moving it to its proper
place in kernel/rcu/rcu.h.
Reported-by: kernel test robot <lkp@intel.com>
[ paulmck: Update per Stephen Rothwell feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Heavy networking load can cause a CPU to execute continuously and
indefinitely within ksoftirqd, in which case there will be no voluntary
task switches and thus no RCU-tasks quiescent states. This commit
therefore causes the exiting rcu_softirq_qs() to provide an RCU-tasks
quiescent state.
This of course means that __do_softirq() and its callers cannot be
invoked from within a tracing trampoline.
Reported-by: Toke Høiland-Jørgensen <toke@redhat.com>
Tested-by: Toke Høiland-Jørgensen <toke@redhat.com>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
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This commit adds a block comment that gives a high-level overview of
how RCU Rude grace periods progress. It also gives an overview of the
memory ordering.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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This commit adds a block comment that gives a high-level overview of how
RCU tasks grace periods progress. It also adds a note about how exiting
tasks are handled, plus it gives an overview of the memory ordering.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Place an early call to start_poll_synchronize_srcu() before the invocation
of call_srcu() on the same srcu_struct structure.
After the later call to srcu_barrier(), the completion of the
first grace period should be visible to a subsequent invocation of
poll_state_synchronize_srcu(), and if not, warn.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Uladzislau Rezki <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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An srcu_struct structure that is initialized before rcu_init_geometry()
will have its srcu_node hierarchy based on CONFIG_NR_CPUS. Once
rcu_init_geometry() is called, this hierarchy is compressed as needed
for the actual maximum number of CPUs for this system.
Later on, that srcu_struct structure is confused, sometimes referring
to its initial CONFIG_NR_CPUS-based hierarchy, and sometimes instead
to the new num_possible_cpus() hierarchy. For example, each of its
->mynode fields continues to reference the original leaf rcu_node
structures, some of which might no longer exist. On the other hand,
srcu_for_each_node_breadth_first() traverses to the new node hierarchy.
There are at least two bad possible outcomes to this:
1) a) A callback enqueued early on an srcu_data structure (call it
*sdp) is recorded pending on sdp->mynode->srcu_data_have_cbs in
srcu_funnel_gp_start() with sdp->mynode pointing to a deep leaf
(say 3 levels).
b) The grace period ends after rcu_init_geometry() shrinks the
nodes level to a single one. srcu_gp_end() walks through the new
srcu_node hierarchy without ever reaching the old leaves so the
callback is never executed.
This is easily reproduced on an 8 CPUs machine with CONFIG_NR_CPUS >= 32
and "rcupdate.rcu_self_test=1". The srcu_barrier() after early tests
verification never completes and the boot hangs:
[ 5413.141029] INFO: task swapper/0:1 blocked for more than 4915 seconds.
[ 5413.147564] Not tainted 5.12.0-rc4+ #28
[ 5413.151927] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 5413.159753] task:swapper/0 state:D stack: 0 pid: 1 ppid: 0 flags:0x00004000
[ 5413.168099] Call Trace:
[ 5413.170555] __schedule+0x36c/0x930
[ 5413.174057] ? wait_for_completion+0x88/0x110
[ 5413.178423] schedule+0x46/0xf0
[ 5413.181575] schedule_timeout+0x284/0x380
[ 5413.185591] ? wait_for_completion+0x88/0x110
[ 5413.189957] ? mark_held_locks+0x61/0x80
[ 5413.193882] ? mark_held_locks+0x61/0x80
[ 5413.197809] ? _raw_spin_unlock_irq+0x24/0x50
[ 5413.202173] ? wait_for_completion+0x88/0x110
[ 5413.206535] wait_for_completion+0xb4/0x110
[ 5413.210724] ? srcu_torture_stats_print+0x110/0x110
[ 5413.215610] srcu_barrier+0x187/0x200
[ 5413.219277] ? rcu_tasks_verify_self_tests+0x50/0x50
[ 5413.224244] ? rdinit_setup+0x2b/0x2b
[ 5413.227907] rcu_verify_early_boot_tests+0x2d/0x40
[ 5413.232700] do_one_initcall+0x63/0x310
[ 5413.236541] ? rdinit_setup+0x2b/0x2b
[ 5413.240207] ? rcu_read_lock_sched_held+0x52/0x80
[ 5413.244912] kernel_init_freeable+0x253/0x28f
[ 5413.249273] ? rest_init+0x250/0x250
[ 5413.252846] kernel_init+0xa/0x110
[ 5413.256257] ret_from_fork+0x22/0x30
2) An srcu_struct structure that is initialized before rcu_init_geometry()
and used afterward will always have stale rdp->mynode references,
resulting in callbacks to be missed in srcu_gp_end(), just like in
the previous scenario.
This commit therefore causes init_srcu_struct_nodes to initialize the
geometry, if needed. This ensures that the srcu_node hierarchy is
properly built and distributed from the get-go.
Suggested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Uladzislau Rezki <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Once srcu_init() is called, the SRCU core will make use of delayed
workqueues, which rely on timers. However init_timers() is called
several steps after rcu_init(). This means that a call_srcu() after
rcu_init() but before init_timers() would find itself within a dangerously
uninitialized timer core.
This commit therefore creates a separate call to srcu_init() after
init_timer() completes, which ensures that we stay in early SRCU mode
until timers are safe(r).
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Uladzislau Rezki <urezki@gmail.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Joel Fernandes <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Pre-srcu_init() invocations of call_srcu() initialize the srcu_struct
structure in question, so there is no need to check this initialization
in srcu_init() when initiating grace periods for srcu_struct structures
that had early call_srcu() invocations. This commit therefore drops
the calls to check_init_srcu_struct() in srcu_init().
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Uladzislau Rezki <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Because alloc_percpu() zeroes out the allocated memory, there is no need
to zero-fill newly allocated per-CPU memory. This commit therefore removes
the loop zeroing the ->srcu_lock_count and ->srcu_unlock_count arrays
from init_srcu_struct_nodes(). This is the only use of that function's
is_static parameter, which this commit also removes.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Uladzislau Rezki <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Fix ~12 single-word typos in RCU code comments.
[ paulmck: Apply feedback from Randy Dunlap. ]
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Now that ->nocb_timer and ->nocb_bypass_timer have become quite similar,
this commit merges them together. A new RCU_NOCB_WAKE_BYPASS wake level
is introduced. As a result, timers perform all kinds of deferred wake
ups but other deferred wakeup callsites only handle non-bypass wakeups
in order not to wake up rcuo too early.
The timer also unconditionally executes a full barrier so as to order
timer_pending() and callback enqueue although the path performing
RCU_NOCB_WAKE_FORCE that makes use of it is debatable. It should also
test against the rdp leader instead of the current rdp.
This unconditional full barrier shouldn't bring visible overhead since
these timers almost never fire.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Tuning the deferred wakeup level must be done from a safe wakeup
point. Currently those sites are:
* ->nocb_timer
* user/idle/guest entry
* CPU down
* softirq/rcuc
All of these sites perform the wake up for both RCU_NOCB_WAKE and
RCU_NOCB_WAKE_FORCE.
In order to merge ->nocb_timer and ->nocb_bypass_timer together, we plan
to add a new RCU_NOCB_WAKE_BYPASS that really should be deferred until
a timer fires so that we don't wake up the NOCB-gp kthread too early.
To prepare for that, this commit specifies the per-callsite wakeup
level/limit.
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
[ paulmck: Fix non-NOCB rcu_nocb_need_deferred_wakeup() definition. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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This commit refrains deleting the ->nocb_timer if rcu_nocb is polling
because it should not ever have been queued in the polling case.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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A NOCB-gp wake p can safely delete the ->nocb_bypass_timer because
nocb_gp_wait() will recheck again the bypass state and rearm the bypass
timer if necessary. This commit therefore deletes this timer.
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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When waking up in nocb_gp_wait(), there is no need to keep the nocb_timer
around because this function will traverse the whole rdp list. Any
update performed before the timer was armed will now be visible after
the ->nocb_gp_lock acquire.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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The only thing that prevented an rdp leader from being de-offloaded was
the nocb_bypass_timer that used to lock the nocb_lock of the rdp leader.
If an rdp gets de-offloaded, it will subtlely ignore rcu_nocb_lock()
calls and do its job in the timer unsafely. Worse yet: If it gets
re-offloaded in the middle of the timer, rcu_nocb_unlock() would try to
unlock, leaving it imbalanced.
Now that the nocb_bypass_timer doesn't use the nocb_lock anymore,
de-offloading the rdp leader is now safe. This commit therefore allows
the rdp leader to be de-offloaded.
Reported-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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The bypass timer calls __call_rcu_nocb_wake() instead of directly
calling __wake_nocb_gp(). The only difference here is that
rdp->qlen_last_fqs_check gets overridden. But resetting the deferred
force quiescent state base shouldn't be relevant for that timer. In fact
the bypass queue in question can be for any rdp from the group and not
necessarily the rdp leader on which the bypass timer is attached.
This commit therefore calls __wake_nocb_gp() directly. This way we
don't even need to lock the ->nocb_lock.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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This reverts commit dcd42591ebb8a25895b551a5297ea9c24414ba54.
The only user was RCU/nocb.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Currently each CPU has its own ->nocb_timer queued when the nocb_gp
wakeup must be deferred. This approach has many drawbacks, compared to
a solution based on a single timer per NOCB group:
* There are a lot of timers to maintain.
* The per-rdp ->nocb_lock must be held to queue and cancel the timer
and this lock can already be heavily contended.
* One timer firing doesn't cancel the other timers in the same group:
- These other timers can thus cause spurious wakeups
- Each rdp that queued a timer must lock both ->nocb_lock and then
->nocb_gp_lock upon exit from the kernel to idle/user/guest mode.
* We can't cancel all of them if we detect an unflushed bypass in
nocb_gp_wait(). In fact currently we only ever cancel the ->nocb_timer
of the leader group.
* The leader group's nocb_timer is cancelled without locking ->nocb_lock
in nocb_gp_wait(). This currently appears to be safe but is an
accident waiting to happen.
* Since the timer acquires ->nocb_lock, it requires extra care in the
NOCB (de-)offloading process, requiring that it be either enabled or
disabled and then flushed.
This commit instead uses the rcuog kthread's CPU's ->nocb_timer instead.
It is protected by nocb_gp_lock, which is _way_ less contended and
remains so even after this change. As a matter of fact, the nocb_timer
almost never fires and the deferred wakeup is mostly carried out upon
idle/user/guest entry. Now the early check performed at this point in
do_nocb_deferred_wakeup() is done on rdp_gp->nocb_defer_wakeup, which
is of course racy. However, this raciness is harmless because we only
need the guarantee that the timer is queued if we were the last one to
queue it. Any other situation (another CPU has queued it and we either
see it or not) is fine.
This solves all the issues listed above.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Currently we have three functions which depend on each other.
Two of them are quite tiny and the last one where the most
work is done. All of them are related to queuing RCU batches
to reclaim objects after a GP.
1. kfree_rcu_monitor(). It consist of few lines. It acquires a spin-lock
and calls kfree_rcu_drain_unlock().
2. kfree_rcu_drain_unlock(). It also consists of few lines of code. It
calls queue_kfree_rcu_work() to queue the batch. If this fails,
it rearms the monitor work to try again later.
3. queue_kfree_rcu_work(). This provides the bulk of the functionality,
attempting to start a new batch to free objects after a GP.
Since there are no external users of functions [2] and [3], both
can eliminated by moving all logic directly into [1], which both
shrinks and simplifies the code.
Also replace comments which start with "/*" to "//" format to make it
unified across the file.
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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The kvfree_rcu() function now defers allocations in the common
case due to the fact that there is no lockless access to the
memory-allocator caches/pools. In addition, in CONFIG_PREEMPT_NONE=y
and in CONFIG_PREEMPT_VOLUNTARY=y kernels, there is no reliable way to
determine if spinlocks are held. As a result, allocation is deferred in
the common case, and the two-argument form of kvfree_rcu() thus uses the
"channel 3" queue through all the rcu_head structures. This channel
is called referred to as the emergency case in comments, and these
comments are now obsolete.
This commit therefore updates these comments to reflect the new
common-case nature of such emergencies.
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Replace an open-coded version of the kfree_rcu_monitor() function body
with a call to that function.
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Before attempting to start a new batch the "monitor_todo" variable is
set to "false" and set back to "true" when a previous RCU batch is still
in progress. This is at best confusing.
Thus change this variable to "false" only when a new batch has been
successfully queued, otherwise, just leave it be.
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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The rcu_scheduler_active flag is set to RCU_SCHEDULER_RUNNING once the
scheduler is up and running. That signal is used in order to check
and queue a "monitor work" to reclaim freed objects (if there are any)
during early boot. This flag is used by kvfree_rcu() to determine when
work can safely be queued, at which point memory passed to earlier
invocations of kvfree_rcu() can be processed.
However, only "krcp->head" is checked for objects that need to be
released, and there are now two more, namely, "krcp->bkvhead[0]" and
"krcp->bkvhead[1]". Therefore, check these two additional channels.
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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nr_bkv_objs is a count of the objects in the kvfree_rcu page cache.
Accessing it requires holding the ->lock. Switch to READ_ONCE() and
WRITE_ONCE() macros to provide lockless access to this counter.
This lockless access is used for the shrinker.
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Add a drain_page_cache() function to drain a per-cpu page cache.
The reason behind of it is a system can run into a low memory
condition, in that case a page shrinker can ask for its users
to free their caches in order to get extra memory available for
other needs in a system.
When a system hits such condition, a page cache is drained for
all CPUs in a system. By default a page cache work is delayed
with 5 seconds interval until a memory pressure disappears, if
needed it can be changed. See a rcu_delay_page_cache_fill_msec
module parameter.
Co-developed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Zqiang <qiang.zhang@windriver.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Sparse reports a warning at rcu_print_task_stall():
"warning: context imbalance in rcu_print_task_stall - unexpected unlock"
The root cause is a missing annotation on rcu_print_task_stall().
This commit therefore adds the missing __releases(rnp->lock) annotation.
Signed-off-by: Jules Irenge <jbi.octave@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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There are a number of places that call out the fact that preempt-disable
regions of code now act as RCU read-side critical sections, where
preempt-disable regions of code include irq-disable regions of code,
bh-disable regions of code, hardirq handlers, and NMI handlers. However,
someone relying solely on (for example) the call_rcu() header comment
might well have no idea that preempt-disable regions of code have RCU
semantics.
This commit therefore updates the header comments for
call_rcu(), synchronize_rcu(), rcu_dereference_bh_check(), and
rcu_dereference_sched_check() to call out these new(ish) forms of RCU
readers.
Reported-by: Michel Lespinasse <michel@lespinasse.org>
[ paulmck: Apply Matthew Wilcox and Michel Lespinasse feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Add comments to synchronize_rcu() and friends that point to
Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Although there are trace events for RCU grace periods, these are only
enabled in CONFIG_RCU_TRACE=y kernels. This commit therefore marks
rcu_gp_cleanup() noinline in order to provide a function that can be
traced that is invoked near the end of each grace period.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Kernels built with CONFIG_RCU_STRICT_GRACE_PERIOD=y can experience
significant lock contention due to RCU's resulting focus on ending grace
periods as soon as possible. This is OK, but only if there are not very
many CPUs. This commit therefore puts this Kconfig option off-limits
to systems with more than four CPUs.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Currently, show_rcu_gp_kthreads() only dumps rcu_node structures that
have outdated ideas of the current grace-period number. This commit
also dumps those that are in any way blocking the current grace period.
This helps diagnose RCU priority boosting failures.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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When any CPU comes online, it checks to see if an RCU-boost kthread has
already been created for that CPU's leaf rcu_node structure, and if
not, it creates one. Unfortunately, it also verifies that this leaf
rcu_node structure actually has at least one online CPU, and if not,
it declines to create the kthread. Although this behavior makes sense
during early boot, especially on systems that claim far more CPUs than
they actually have, it makes no sense for the first CPU to come online
for a given rcu_node structure. There is no point in checking because
we know there is a CPU on its way in.
The problem is that timing differences can cause this incoming CPU to not
yet be reflected in the various bit masks even at rcutree_online_cpu()
time, and there is no chance at rcutree_prepare_cpu() time. Plus it
would be better to create the RCU-boost kthread at rcutree_prepare_cpu()
to handle the case where the CPU is involved in an RCU priority inversion
very shortly after it comes online.
This commit therefore moves the checking to rcu_prepare_kthreads(), which
is called only at early boot, when the check is appropriate. In addition,
it makes rcutree_prepare_cpu() invoke rcu_spawn_one_boost_kthread(), which
no longer does any checking for online CPUs.
With this change, RCU priority boosting tests now pass for short rcutorture
runs, even with single-CPU leaf rcu_node structures.
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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This commit adds each rcu_node structure's ->qsmask and "bBEG" output
indicating whether: (1) There is a boost kthread, (2) A reader needs
to be (or is in the process of being) boosted, (3) A reader is blocking
an expedited grace period, and (4) A reader is blocking a normal grace
period. This helps diagnose RCU priority boosting failures.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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If another lockdep report runs concurrently with an RCU lockdep report
from RCU_LOCKDEP_WARN(), the following sequence of events can occur:
1. debug_lockdep_rcu_enabled() sees that lockdep is enabled
when called from (say) synchronize_rcu().
2. Lockdep is disabled by a concurrent lockdep report.
3. debug_lockdep_rcu_enabled() evaluates its lockdep-expression
argument, for example, lock_is_held(&rcu_bh_lock_map).
4. Because lockdep is now disabled, lock_is_held() plays it safe and
returns the constant 1.
5. But in this case, the constant 1 is not safe, because invoking
synchronize_rcu() under rcu_read_lock_bh() is disallowed.
6. debug_lockdep_rcu_enabled() wrongly invokes lockdep_rcu_suspicious(),
resulting in a false-positive splat.
This commit therefore changes RCU_LOCKDEP_WARN() to check
debug_lockdep_rcu_enabled() after checking the lockdep expression,
so that any "safe" returns from lock_is_held() are rejected by
debug_lockdep_rcu_enabled(). This requires memory ordering, which is
supplied by READ_ONCE(debug_locks). The resulting volatile accesses
prevent the compiler from reordering and the fact that only one variable
is being accessed prevents the underlying hardware from reordering.
The combination works for IA64, which can reorder reads to the same
location, but this is defeated by the volatile accesses, which compile
to load instructions that provide ordering.
Reported-by: syzbot+dde0cc33951735441301@syzkaller.appspotmail.com
Reported-by: Matthew Wilcox <willy@infradead.org>
Reported-by: syzbot+88e4f02896967fe1ab0d@syzkaller.appspotmail.com
Reported-by: Thomas Gleixner <tglx@linutronix.de>
Suggested-by: Boqun Feng <boqun.feng@gmail.com>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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