Commit graph

987 commits

Author SHA1 Message Date
Paul E. McKenney
53b46303da rcu: Remove rsp parameter from rcu_boot_init_percpu_data() and friends
There now is only one rcu_state structure in a given build of
the Linux kernel, so there is no need to pass it as a parameter
to RCU's functions.  This commit therefore removes the rsp
parameter from rcu_boot_init_percpu_data(), rcu_init_percpu_data(),
rcu_cleanup_dying_idle_cpu(), and rcu_migrate_callbacks().  While in
the neighborhood, line the last three into rcutree_prepare_cpu(),
rcu_report_dead() and rcutree_migrate_callbacks(), respectively.
This also gets rid of the for_each_rcu_flavor() calls that were in
those tree functions.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:03:08 -07:00
Paul E. McKenney
8344b871b1 rcu: Remove rsp parameter from _rcu_barrier() and friends
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
_rcu_barrier_trace() and _rcu_barrier().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:03:08 -07:00
Paul E. McKenney
98ece508b5 rcu: Remove rsp parameter from __rcu_pending()
There now is only one rcu_state structure in a given build of the Linux
kernel, so there is no need to pass it as a parameter to RCU's functions.
This commit therefore removes the rsp parameter from __rcu_pending(),
and also inlines it into rcu_pending(), removing the for_each_rcu_flavor()
while in the neighborhood..

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:03:07 -07:00
Paul E. McKenney
5c7d89676b rcu: Remove rsp parameter from __call_rcu() and friend
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
__call_rcu_core() and __call_rcu().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:03:07 -07:00
Paul E. McKenney
b049fdf8e3 rcu: Remove rsp parameter from __rcu_process_callbacks()
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
__rcu_process_callbacks(), and also inlines it into rcu_process_callbacks(),
removing the for_each_rcu_flavor() while in the neighborhood.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:03:06 -07:00
Paul E. McKenney
b96f9dc4fb rcu: Remove rsp parameter from rcu_check_gp_start_stall()
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
rcu_check_gp_start_stall().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:03:06 -07:00
Paul E. McKenney
e9ecb780fe rcu: Remove rsp parameter from force-quiescent-state functions
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
force_qs_rnp() and force_quiescent_state().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:03:05 -07:00
Paul E. McKenney
5bb5d09cc4 rcu: Remove rsp parameter from rcu_do_batch()
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
rcu_do_batch().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:03:05 -07:00
Paul E. McKenney
780cd59083 rcu: Remove rsp parameter from CPU hotplug functions
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
rcu_cleanup_dying_cpu() and rcu_cleanup_dead_cpu().  And, as long as
we are in the neighborhood, inlines them into rcutree_dying_cpu() and
rcutree_dead_cpu(), respectively.  This also eliminates a pair of
for_each_rcu_flavor() loops.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:03:04 -07:00
Paul E. McKenney
8087d3e3c4 rcu: Remove rsp parameter from rcu_check_quiescent_state()
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
rcu_check_quiescent_state().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:03:04 -07:00
Paul E. McKenney
0854a05c9f rcu: Remove rsp parameter from rcu_gp_kthread() and friends
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
rcu_gp_init(), rcu_gp_fqs_check_wake(), rcu_gp_fqs(), rcu_gp_cleanup(),
and rcu_gp_kthread().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:03:03 -07:00
Paul E. McKenney
22212332c1 rcu: Remove rsp parameter from rcu_gp_slow()
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
rcu_gp_slow().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:03:03 -07:00
Paul E. McKenney
15cabdffbb rcu: Remove rsp parameter from note_gp_changes()
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
note_gp_changes().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:03:02 -07:00
Paul E. McKenney
c7e48f7ba3 rcu: Remove rsp parameter from __note_gp_changes()
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
__note_gp_changes().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:03:01 -07:00
Paul E. McKenney
834f56bf54 rcu: Remove rsp parameter from rcu_advance_cbs()
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
rcu_advance_cbs().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:03:01 -07:00
Paul E. McKenney
c6e09b97b9 rcu: Remove rsp parameter from rcu_accelerate_cbs_unlocked()
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
rcu_accelerate_cbs_unlocked().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:03:00 -07:00
Paul E. McKenney
02f501423d rcu: Remove rsp parameter from rcu_accelerate_cbs()
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
rcu_accelerate_cbs().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:03:00 -07:00
Paul E. McKenney
532c00c97f rcu: Remove rsp parameter from rcu_gp_kthread_wake()
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
rcu_gp_kthread_wake().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:59 -07:00
Paul E. McKenney
3481f2eab0 rcu: Remove rsp parameter from rcu_future_gp_cleanup()
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
rcu_future_gp_cleanup().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:59 -07:00
Paul E. McKenney
ea12ff2b7d rcu: Remove rsp parameter from check_cpu_stall()
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
check_cpu_stall().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:58 -07:00
Paul E. McKenney
4e8b8e08f9 rcu: Remove rsp parameter from print_cpu_stall()
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
print_cpu_stall().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:58 -07:00
Paul E. McKenney
a91e7e58b1 rcu: Remove rsp parameter from print_other_cpu_stall()
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
print_other_cpu_stall().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:57 -07:00
Paul E. McKenney
e1741c69d4 rcu: Remove rsp parameter from rcu_stall_kick_kthreads()
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
rcu_stall_kick_kthreads().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:57 -07:00
Paul E. McKenney
33dbdbf025 rcu: Remove rsp parameter from rcu_dump_cpu_stacks()
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
rcu_dump_cpu_stacks().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:56 -07:00
Paul E. McKenney
8fd119b652 rcu: Remove rsp parameter from rcu_check_gp_kthread_starvation()
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
rcu_check_gp_kthread_starvation().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:56 -07:00
Paul E. McKenney
ad3832e974 rcu: Remove rsp parameter from record_gp_stall_check_time()
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
record_gp_stall_check_time().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:55 -07:00
Paul E. McKenney
336a4f6c45 rcu: Remove rsp parameter from rcu_get_root()
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
rcu_get_root().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:55 -07:00
Paul E. McKenney
de8e87305a rcu: Remove rsp parameter from rcu_gp_in_progress()
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
rcu_gp_in_progress().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:54 -07:00
Paul E. McKenney
33085c469a rcu: Remove rsp parameter from rcu_report_qs_rdp()
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
rcu_report_qs_rdp().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:53 -07:00
Paul E. McKenney
139ad4da5a rcu: Remove rsp parameter from rcu_report_unblock_qs_rnp()
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
rcu_report_unblock_qs_rnp(), which is particularly appropriate in
this case given that this parameter is no longer used.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:53 -07:00
Paul E. McKenney
aff4e9ede5 rcu: Remove rsp parameter from rcu_report_qs_rsp()
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
rcu_report_qs_rsp().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:52 -07:00
Paul E. McKenney
b50912d0b5 rcu: Remove rsp parameter from rcu_report_qs_rnp()
There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
rcu_report_qs_rnp().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:51 -07:00
Paul E. McKenney
2280ee5a7d rcu: Remove rcu_data_p pointer to default rcu_data structure
The rcu_data_p pointer references the default set of per-CPU rcu_data
structures, that is, those that call_rcu() uses, as opposed to
call_rcu_bh() and sometimes call_rcu_sched().  But there is now only one
set of per-CPU rcu_data structures, so that one set is by definition
the default, which means that the rcu_data_p pointer no longer serves
any useful purpose.  This commit therefore removes it.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:51 -07:00
Paul E. McKenney
16fc9c600b rcu: Remove rcu_state_p pointer to default rcu_state structure
The rcu_state_p pointer references the default rcu_state structure,
that is, the one that call_rcu() uses, as opposed to call_rcu_bh()
and sometimes call_rcu_sched().  But there is now only one rcu_state
structure, so that one structure is by definition the default, which
means that the rcu_state_p pointer no longer serves any useful purpose.
This commit therefore removes it.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:50 -07:00
Paul E. McKenney
da1df50d16 rcu: Remove rcu_state structure's ->rda field
The rcu_state structure's ->rda field was used to find the per-CPU
rcu_data structures corresponding to that rcu_state structure.  But now
there is only one rcu_state structure (creatively named "rcu_state")
and one set of per-CPU rcu_data structures (creatively named "rcu_data").
Therefore, uses of the ->rda field can always be replaced by "rcu_data,
and this commit makes that change and removes the ->rda field.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:49 -07:00
Paul E. McKenney
ec5dd444b6 rcu: Eliminate rcu_state structure's ->call field
The rcu_state structure's ->call field references the corresponding RCU
flavor's call_rcu() function.  However, now that there is only ever one
rcu_state structure in a given build of the Linux kernel, and that flavor
uses plain old call_rcu(), there is not a lot of point in continuing to
have the ->call field.  This commit therefore removes it.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:48 -07:00
Paul E. McKenney
358be2d368 rcu: Remove RCU_STATE_INITIALIZER()
Now that a given build of the Linux kernel has only one set of rcu_state,
rcu_node, and rcu_data structures, there is no point in creating a macro
to declare and compile-time initialize them.  This commit therefore
just does normal declaration and compile-time initialization of these
structures.  While in the area, this commit also removes #ifndefs of
the no-longer-ever-defined preprocessor macro RCU_TREE_NONCORE.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:47 -07:00
Paul E. McKenney
709fdce754 rcu: Express Tiny RCU updates in terms of RCU rather than RCU-sched
This commit renames Tiny RCU functions so that the lowest level of
functionality is RCU (e.g., synchronize_rcu()) rather than RCU-sched
(e.g., synchronize_sched()).  This provides greater naming compatibility
with Tree RCU, which will in turn permit more LoC removal once
the RCU-sched and RCU-bh update-side API is removed.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Fix Tiny call_rcu()'s EXPORT_SYMBOL() in response to a bug
  report from kbuild test robot. ]
2018-08-30 16:02:46 -07:00
Paul E. McKenney
45975c7d21 rcu: Define RCU-sched API in terms of RCU for Tree RCU PREEMPT builds
Now that RCU-preempt knows about preemption disabling, its implementation
of synchronize_rcu() works for synchronize_sched(), and likewise for the
other RCU-sched update-side API members.  This commit therefore confines
the RCU-sched update-side code to CONFIG_PREEMPT=n builds, and defines
RCU-sched's update-side API members in terms of those of RCU-preempt.

This means that any given build of the Linux kernel has only one
update-side flavor of RCU, namely RCU-preempt for CONFIG_PREEMPT=y builds
and RCU-sched for CONFIG_PREEMPT=n builds.  This in turn means that kernels
built with CONFIG_RCU_NOCB_CPU=y have only one rcuo kthread per CPU.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Andi Kleen <ak@linux.intel.com>
2018-08-30 16:02:45 -07:00
Paul E. McKenney
4cf439a200 rcu: Fix typo in rcu_get_gp_kthreads_prio() header comment
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:43 -07:00
Paul E. McKenney
2bbfc25b09 rcu: Drop "wake" parameter from rcu_report_exp_rdp()
The rcu_report_exp_rdp() function is always invoked with its "wake"
argument set to "true", so this commit drops this parameter.  The only
potential call site that would use "false" is in the code driving the
expedited grace period, and that code uses rcu_report_exp_cpu_mult()
instead, which therefore retains its "wake" parameter.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:43 -07:00
Paul E. McKenney
82fcecfa81 rcu: Update comments and help text for no more RCU-bh updaters
This commit updates comments and help text to account for the fact that
RCU-bh update-side functions are now simple wrappers for their RCU or
RCU-sched counterparts.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:42 -07:00
Paul E. McKenney
65cfe3583b rcu: Define RCU-bh update API in terms of RCU
Now that the main RCU API knows about softirq disabling and softirq's
quiescent states, the RCU-bh update code can be dispensed with.
This commit therefore removes the RCU-bh update-side implementation and
defines RCU-bh's update-side API in terms of that of either RCU-preempt or
RCU-sched, depending on the setting of the CONFIG_PREEMPT Kconfig option.

In kernels built with CONFIG_RCU_NOCB_CPU=y this has the knock-on effect
of reducing by one the number of rcuo kthreads per CPU.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:40 -07:00
Paul E. McKenney
ba1c64c272 rcu: Report expedited grace periods at context-switch time
This commit reduces the latency of expedited RCU grace periods by
reporting a quiescent state for the CPU at context-switch time.
In CONFIG_PREEMPT=y kernels, if the outgoing task is still within an
RCU read-side critical section (and thus still blocking some grace
period, perhaps including this expedited grace period), then that task
will already have been placed on one of the leaf rcu_node structures'
->blkd_tasks list.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:38 -07:00
Paul E. McKenney
d28139c4e9 rcu: Apply RCU-bh QSes to RCU-sched and RCU-preempt when safe
One necessary step towards consolidating the three flavors of RCU is to
make sure that the resulting consolidated "one flavor to rule them all"
correctly handles networking denial-of-service attacks.  One thing that
allows RCU-bh to do so is that __do_softirq() invokes rcu_bh_qs() every
so often, and so something similar has to happen for consolidated RCU.

This must be done carefully.  For example, if a preemption-disabled
region of code takes an interrupt which does softirq processing before
returning, consolidated RCU must ignore the resulting rcu_bh_qs()
invocations -- preemption is still disabled, and that means an RCU
reader for the consolidated flavor.

This commit therefore creates a new rcu_softirq_qs() that is called only
from the ksoftirqd task, thus avoiding the interrupted-a-preempted-region
problem.  This new rcu_softirq_qs() function invokes rcu_sched_qs(),
rcu_preempt_qs(), and rcu_preempt_deferred_qs().  The latter call handles
any deferred quiescent states.

Note that __do_softirq() still invokes rcu_bh_qs().  It will continue to
do so until a later stage of cleanup when the RCU-bh flavor is removed.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Fix !SMP issue located by kbuild test robot. ]
2018-08-30 16:02:38 -07:00
Paul E. McKenney
e11ec65cc8 rcu: Add warning to detect half-interrupts
RCU's dyntick-idle code is written to tolerate half-interrupts, that it,
either an interrupt that invokes rcu_irq_enter() but never invokes the
corresponding rcu_irq_exit() on the one hand, or an interrupt that never
invokes rcu_irq_enter() but does invoke the "corresponding" rcu_irq_exit()
on the other.  These things really did happen at one time, as evidenced
by this ca-2011 LKML post:

http://lkml.kernel.org/r/20111014170019.GE2428@linux.vnet.ibm.com

The reason why RCU tolerates half-interrupts is that usermode helpers
used exceptions to invoke a system call from within the kernel such that
the system call did a normal return (not a return from exception) to
the calling context.  This caused rcu_irq_enter() to be invoked without
a matching rcu_irq_exit().  However, usermode helpers have since been
rewritten to make much more housebroken use of workqueues, kernel threads,
and do_execve(), and therefore should no longer produce half-interrupts.
No one knows of any other source of half-interrupts, but then again,
no one seems insane enough to go audit the entire kernel to verify that
half-interrupts really are a relic of the past.

This commit therefore adds a pair of WARN_ON_ONCE() calls that will
trigger in the presence of half interrupts, which the code will continue
to handle correctly.  If neither of these WARN_ON_ONCE() trigger by
mid-2021, then perhaps RCU can stop handling half-interrupts, which
would be a considerable simplification.

Reported-by: Steven Rostedt <rostedt@goodmis.org>
Reported-by: Joel Fernandes <joel@joelfernandes.org>
Reported-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
2018-08-30 16:02:36 -07:00
Paul E. McKenney
fcc878e4df rcu: Remove now-unused ->b.exp_need_qs field from the rcu_special union
The ->b.exp_need_qs field is now set only to false, so this commit
removes it.  The job this field used to do is now done by the rcu_data
structure's ->deferred_qs field, which is a consequence of a better
split between task-based (the rcu_node structure's ->exp_tasks field) and
CPU-based (the aforementioned rcu_data structure's ->deferred_qs field)
tracking of quiescent states for RCU-preempt expedited grace periods.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:36 -07:00
Paul E. McKenney
27c744e32a rcu: Allow processing deferred QSes for exiting RCU-preempt readers
If an RCU-preempt read-side critical section is exiting, that is,
->rcu_read_lock_nesting is negative, then it is a good time to look
at the possibility of reporting deferred quiescent states.  This
commit therefore updates the checks in rcu_preempt_need_deferred_qs()
to allow exiting critical sections to report deferred quiescent states.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:35 -07:00
Paul E. McKenney
c0335743c5 rcutorture: Test extended "rcu" read-side critical sections
This commit makes the "rcu" torture type test extended read-side
critical sections in order to test the deferral of RCU-preempt
quiescent-state testing.

In CONFIG_PREEMPT=n kernels, this simply duplicates the setup already
in place for the "sched" torture type.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 16:02:35 -07:00
Paul E. McKenney
3e31009898 rcu: Defer reporting RCU-preempt quiescent states when disabled
This commit defers reporting of RCU-preempt quiescent states at
rcu_read_unlock_special() time when any of interrupts, softirq, or
preemption are disabled.  These deferred quiescent states are reported
at a later RCU_SOFTIRQ, context switch, idle entry, or CPU-hotplug
offline operation.  Of course, if another RCU read-side critical
section has started in the meantime, the reporting of the quiescent
state will be further deferred.

This also means that disabling preemption, interrupts, and/or
softirqs will act as an RCU-preempt read-side critical section.
This is enforced by checking preempt_count() as needed.

Some special cases must be handled on an ad-hoc basis, for example,
context switch is a quiescent state even though both the scheduler and
do_exit() disable preemption.  In these cases, additional calls to
rcu_preempt_deferred_qs() override the preemption disabling.  Similar
logic overrides disabled interrupts in rcu_preempt_check_callbacks()
because in this case the quiescent state happened just before the
corresponding scheduling-clock interrupt.

In theory, this change lifts a long-standing restriction that required
that if interrupts were disabled across a call to rcu_read_unlock()
that the matching rcu_read_lock() also be contained within that
interrupts-disabled region of code.  Because the reporting of the
corresponding RCU-preempt quiescent state is now deferred until
after interrupts have been enabled, it is no longer possible for this
situation to result in deadlocks involving the scheduler's runqueue and
priority-inheritance locks.  This may allow some code simplification that
might reduce interrupt latency a bit.  Unfortunately, in practice this
would also defer deboosting a low-priority task that had been subjected
to RCU priority boosting, so real-time-response considerations might
well force this restriction to remain in place.

Because RCU-preempt grace periods are now blocked not only by RCU
read-side critical sections, but also by disabling of interrupts,
preemption, and softirqs, it will be possible to eliminate RCU-bh and
RCU-sched in favor of RCU-preempt in CONFIG_PREEMPT=y kernels.  This may
require some additional plumbing to provide the network denial-of-service
guarantees that have been traditionally provided by RCU-bh.  Once these
are in place, CONFIG_PREEMPT=n kernels will be able to fold RCU-bh
into RCU-sched.  This would mean that all kernels would have but
one flavor of RCU, which would open the door to significant code
cleanup.

Moving to a single flavor of RCU would also have the beneficial effect
of reducing the NOCB kthreads by at least a factor of two.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Apply rcu_read_unlock_special() preempt_count() feedback
  from Joel Fernandes. ]
[ paulmck: Adjust rcu_eqs_enter() call to rcu_preempt_deferred_qs() in
  response to bug reports from kbuild test robot. ]
[ paulmck: Fix bug located by kbuild test robot involving recursion
  via rcu_preempt_deferred_qs(). ]
2018-08-30 16:02:34 -07:00