13 Jan, 2010
7 commits
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Because a new grace period cannot start while we are executing
within the force_quiescent_state() function's switch statement,
if any test within that switch statement or within any function
called from that switch statement shows that the current grace
period has ended, we can safely re-do that test any time before
we leave the switch statement. This means that we no longer
need a return value from rcu_process_dyntick(), as we can simply
invoke rcu_gp_in_progress() to check whether the old grace
period has finished -- there is no longer any need to worry
about whether or not a new grace period has been started.Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar -
At this point, the second argument to all calls to
rcu_process_dyntick() is a function of the same field of the
structure passed in as the first argument, namely, rsp->gpnum-1.
So propagate rsp->gpnum-1 to all uses of the second argument
within rcu_process_dyntick() and then eliminate the second
argument.Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar -
Because rsp->fqs_active is set to 1 across
force_quiescent_state()'s switch statement, rcu_start_gp() will
refrain from starting a new grace period during this time.
Therefore, rsp->gpnum is constant, and can be propagated to all
uses of lastcomp, eliminating this local variable.Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar -
Because the root rcu_node lock is held across entry to the
switch statement in force_quiescent_state(), it is no longer
necessary to snapshot rsp->signaled to a local variable.
Eliminate both the snapshotting and the local variable.Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar -
Reduce the number and variety of race conditions by prohibiting
the start of a new grace period while force_quiescent_state() is
active. A new fqs_active flag in the rcu_state structure is used
to trace whether or not force_quiescent_state() is active, and
this new flag is tested by rcu_start_gp(). If the CPU that
closed out the last grace period needs another grace period,
this new grace period may be delayed up to one scheduling-clock
tick, but it will eventually get started.Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar -
This patch releases rnp->lock after the end of
force_quiescent_state()'s switch statement. This is a second
step towards prohibiting starting grace periods while
force_quiescent_state() is executing, which will reduce the
number and complexity of races that force_quiescent_state() is
involved in.Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar -
This causes rnp->lock to be held on entry to
force_quiescent_state()'s switch statement. This is a first
step towards prohibiting starting grace periods while
force_quiescent_state() is executing, which will reduce the
number and complexity of races that force_quiescent_state() is
involved in.Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar
03 Dec, 2009
3 commits
-
Implement an synchronize_rcu_expedited() for preemptible RCU
that actually is expedited. This uses
synchronize_sched_expedited() to force all threads currently
running in a preemptible-RCU read-side critical section onto the
appropriate ->blocked_tasks[] list, then takes a snapshot of all
of these lists and waits for them to drain.Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar -
Enable a fourth level of rcu_node hierarchy for TREE_RCU and
TREE_PREEMPT_RCU. This is for stress-testing and experiemental
purposes only, although in theory this would enable 16,777,216
CPUs on 64-bit systems, though only 1,048,576 CPUs on 32-bit
systems. Normal experimental use of this fourth level will
normally set CONFIG_RCU_FANOUT=2, requiring a 16-CPU system,
though the more adventurous (and more fortunate) experimenters
may wish to chose CONFIG_RCU_FANOUT=3 for 81-CPU systems or even
CONFIG_RCU_FANOUT=4 for 256-CPU systems.Signed-off-by: Paul E. McKenney
Acked-by: Josh Triplett
Acked-by: Lai Jiangshan
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar -
The number of "quiet" functions has grown recently, and the
names are no longer very descriptive. The point of all of these
functions is to do some portion of the task of reporting a
quiescent state, so rename them accordingly:o cpu_quiet() becomes rcu_report_qs_rdp(), which reports a
quiescent state to the per-CPU rcu_data structure. If this
turns out to be a new quiescent state for this grace period,
then rcu_report_qs_rnp() will be invoked to propagate the
quiescent state up the rcu_node hierarchy.o cpu_quiet_msk() becomes rcu_report_qs_rnp(), which reports
a quiescent state for a given CPU (or possibly a set of CPUs)
up the rcu_node hierarchy.o cpu_quiet_msk_finish() becomes rcu_report_qs_rsp(), which
reports a full set of quiescent states to the global rcu_state
structure.o task_quiet() becomes rcu_report_unblock_qs_rnp(), which reports
a quiescent state due to a task exiting an RCU read-side critical
section that had previously blocked in that same critical section.
As indicated by the new name, this type of quiescent state is
reported up the rcu_node hierarchy (using rcu_report_qs_rnp()
to do so).Signed-off-by: Paul E. McKenney
Acked-by: Josh Triplett
Acked-by: Lai Jiangshan
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar
23 Nov, 2009
3 commits
-
Remove #ifdefs from kernel/rcupdate.c and
include/linux/rcupdate.h by moving code to
include/linux/rcutiny.h, include/linux/rcutree.h, and
kernel/rcutree.c.Also remove some definitions that are no longer used.
Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar -
The functions rcu_init() is a wrapper for __rcu_init(), and also
sets up the CPU-hotplug notifier for rcu_barrier_cpu_hotplug().
But TINY_RCU doesn't need CPU-hotplug notification, and the
rcu_barrier_cpu_hotplug() is a simple wrapper for
rcu_cpu_notify().So push rcu_init() out to kernel/rcutree.c and kernel/rcutiny.c
and get rid of the wrapper function rcu_barrier_cpu_hotplug().Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar -
When the last CPU of a given leaf rcu_node structure goes
offline, all of the tasks queued on that leaf rcu_node structure
(due to having blocked in their current RCU read-side critical
sections) are requeued onto the root rcu_node structure. This
requeuing is carried out by rcu_preempt_offline_tasks().
However, it is possible that these queued tasks are the only
thing preventing the leaf rcu_node structure from reporting a
quiescent state up the rcu_node hierarchy. Unfortunately, the
old code would fail to do this reporting, resulting in a
grace-period stall given the following sequence of events:1. Kernel built for more than 32 CPUs on 32-bit systems or for more
than 64 CPUs on 64-bit systems, so that there is more than one
rcu_node structure. (Or CONFIG_RCU_FANOUT is artificially set
to a number smaller than CONFIG_NR_CPUS.)2. The kernel is built with CONFIG_TREE_PREEMPT_RCU.
3. A task running on a CPU associated with a given leaf rcu_node
structure blocks while in an RCU read-side critical section
-and- that CPU has not yet passed through a quiescent state
for the current RCU grace period. This will cause the task
to be queued on the leaf rcu_node's blocked_tasks[] array, in
particular, on the element of this array corresponding to the
current grace period.4. Each of the remaining CPUs corresponding to this same leaf rcu_node
structure pass through a quiescent state. However, the task is
still in its RCU read-side critical section, so these quiescent
states cannot be reported further up the rcu_node hierarchy.
Nevertheless, all bits in the leaf rcu_node structure's ->qsmask
field are now zero.5. Each of the remaining CPUs go offline. (The events in step
#4 and #5 can happen in any order as long as each CPU passes
through a quiescent state before going offline.)6. When the last CPU goes offline, __rcu_offline_cpu() will invoke
rcu_preempt_offline_tasks(), which will move the task to the
root rcu_node structure, but without reporting a quiescent state
up the rcu_node hierarchy (and this failure to report a quiescent
state is the bug).But because this leaf rcu_node structure's ->qsmask field is
already zero and its ->block_tasks[] entries are all empty,
force_quiescent_state() will skip this rcu_node structure.Therefore, grace periods are now hung.
This patch abstracts some code out of rcu_read_unlock_special(),
calling the result task_quiet() by analogy with cpu_quiet(), and
invokes task_quiet() from both rcu_read_lock_special() and
__rcu_offline_cpu(). Invoking task_quiet() from
__rcu_offline_cpu() reports the quiescent state up the rcu_node
hierarchy, fixing the bug. This ends up requiring a separate
lock_class_key per level of the rcu_node hierarchy, which this
patch also provides.Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar
14 Nov, 2009
2 commits
-
Now that there are both ->gpnum and ->completed fields in the
rcu_node structure, __rcu_pending() should check rdp->gpnum and
rdp->completed against rnp->gpnum and rdp->completed, respectively,
instead of the prior comparison against the rcu_state fields
rsp->gpnum and rsp->completed.Given the old comparison, __rcu_pending() could return 1, resulting
in a needless raise_softirq(RCU_SOFTIRQ). This useless work would
happen if RCU responded to a scheduling-clock interrupt after the
rcu_state fields had been updated, but before the rcu_node fields
had been updated.Changing the comparison from the rcu_state fields to the rcu_node
fields prevents this useless work from happening.Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar -
Now that a copy of the rsp->completed flag is available in all
rcu_node structures, make full use of it. It is still
legitimate to access rsp->completed while holding the root
rcu_node structure's lock, however.Also, tighten up force_quiescent_state()'s checks for end of
current grace period.Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar
13 Nov, 2009
2 commits
-
The force_quiescent_state() function also took a snapshot
of the ->completed field, which was as obnoxious as it was in
rcu_sched_qs() and friends. So snapshot ->gpnum-1.Also, since the dyntick_record_completed() and
dyntick_recall_completed() functions are now simple assignments
that are independent of CONFIG_NO_HZ, and since their names are
now misleading, get rid of them.Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar -
An earlier fix for a race resulted in a situation where the CPUs
other than the CPU that detected the end of the grace period would
not process their callbacks until the next grace period started.This means that these other CPUs would unnecessarily demand that an
extra grace period be started.This patch eliminates this extra grace period and speeds callback
processing by propagating rsp->completed to the rcu_node structures
in the case where the CPU detecting the end of the grace period
sees no reason to start a new grace period.Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar
11 Nov, 2009
2 commits
-
The rdp->passed_quiesc_completed fields are used to properly
associate the recorded quiescent state with a grace period. It
is OK to wrongly associate a given quiescent state with a
preceding grace period, but it is fatal to associate a given
quiescent state with a grace period that begins after the
quiescent state occurred. Grace periods are numbered, and the
following fields track them:o ->gpnum is the number of the grace period currently in
progress, or the number of the last grace period to
complete if no grace period is currently in progress.o ->completed is the number of the last grace period to
have completed.These two fields are equal if there is no grace period in
progress, otherwise ->gpnum is one greater than ->completed.
But the rdp->passed_quiesc_completed field compared against
->completed, and if equal, the quiescent state is presumed to
count against the current grace period.The earlier code copied rdp->completed to
rdp->passed_quiesc_completed, which has been made to work, but
is error-prone. In contrast, copying one less than rdp->gpnum
is guaranteed safe, because rdp->gpnum is not incremented until
after the start of the corresponding grace period. At the end of
the grace period, when ->completed has incremented, then any
quiescent periods recorded previously will be discarded.Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar -
This field is used whether or not CONFIG_NO_HZ is set, so the
old name of ->dynticks_completed is quite misleading.Change to ->completed_fqs, given that it the value that
force_quiescent_state() is trying to drive the ->completed field
away from.Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar
10 Nov, 2009
4 commits
-
Impose a clear locking design on the note_new_gpnum()
function's use of the ->gpnum counter. This is done by updating
rdp->gpnum only from the corresponding leaf rcu_node structure's
rnp->gpnum field, and even then only under the protection of
that same rcu_node structure's ->lock field. Performance and
scalability are maintained using a form of double-checked
locking, and excessive spinning is avoided by use of the
spin_trylock() function. The use of spin_trylock() is safe due
to the fact that CPUs who fail to acquire this lock will try
again later. The hierarchical nature of the rcu_node data
structure limits contention (which could be limited further if
need be using the RCU_FANOUT kernel parameter).Without this patch, obscure but quite possible races could
result in a quiescent state that occurred during one grace
period to be accounted to the following grace period, causing
this following grace period to end prematurely. Not good!Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
Cc: # .32.x
LKML-Reference:
Signed-off-by: Ingo Molnar -
Impose a clear locking design on the rcu_process_gp_end()
function's use of the ->completed counter. This is done by
creating a ->completed field in the rcu_node structure, which
can safely be accessed under the protection of that structure's
lock. Performance and scalability are maintained by using a
form of double-checked locking, so that rcu_process_gp_end()
only acquires the leaf rcu_node structure's ->lock if a grace
period has recently ended.This fix reduces rcutorture failure rate by at least two orders
of magnitude under heavy stress with force_quiescent_state()
being invoked artificially often. Without this fix,
unsynchronized access to the ->completed field can cause
rcu_process_gp_end() to advance callbacks whose grace period has
not yet expired. (Bad idea!)Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
Cc: # .32.x
LKML-Reference:
Signed-off-by: Ingo Molnar -
Impose a clear locking design on non-NO_HZ handling of the
->completed counter. This increases the distance between the
RCU and the CPU-hotplug mechanisms.Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
Cc: # .32.x
LKML-Reference:
Signed-off-by: Ingo Molnar -
Merge reason: Pick up RCU fixlet to base further commits on.
Signed-off-by: Ingo Molnar
02 Nov, 2009
1 commit
-
Very long RCU read-side critical sections (50 milliseconds or
so) can cause a race between force_quiescent_state() and
rcu_start_gp() as follows on kernel builds with multi-level
rcu_node hierarchies:1. CPU 0 calls force_quiescent_state(), sees that there is a
grace period in progress, and acquires ->fsqlock.2. CPU 1 detects the end of the grace period, and so
cpu_quiet_msk_finish() sets rsp->completed to rsp->gpnum.
This operation is carried out under the root rnp->lock,
but CPU 0 has not yet acquired that lock. Note that
rsp->signaled is still RCU_SAVE_DYNTICK from the last
grace period.3. CPU 1 calls rcu_start_gp(), but no one wants a new grace
period, so it drops the root rnp->lock and returns.4. CPU 0 acquires the root rnp->lock and picks up rsp->completed
and rsp->signaled, then drops rnp->lock. It then enters the
RCU_SAVE_DYNTICK leg of the switch statement.5. CPU 2 invokes call_rcu(), and now needs a new grace period.
It calls rcu_start_gp(), which acquires the root rnp->lock, sets
rsp->signaled to RCU_GP_INIT (too bad that CPU 0 is already in
the RCU_SAVE_DYNTICK leg of the switch statement!) and starts
initializing the rcu_node hierarchy. If there are multiple
levels to the hierarchy, it will drop the root rnp->lock and
initialize the lower levels of the hierarchy.6. CPU 0 notes that rsp->completed has not changed, which permits
both CPU 2 and CPU 0 to try updating it concurrently. If CPU 0's
update prevails, later calls to force_quiescent_state() can
count old quiescent states against the new grace period, which
can in turn result in premature ending of grace periods.Not good.
This patch adds an RCU_GP_IDLE state for rsp->signaled that is
set initially at boot time and any time a grace period ends.
This prevents CPU 0 from getting into the workings of
force_quiescent_state() in step 4. Additional locking and
checks prevent the concurrent update of rsp->signaled in step 6.Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar
27 Oct, 2009
1 commit
-
Use lockdep_set_class() to simplify the code and to avoid any
additional overhead in the !LOCKDEP case. Also move the
definition of rcu_root_class into kernel/rcutree.c, as suggested
by Lai Jiangshan.Signed-off-by: Peter Zijlstra
Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar
16 Oct, 2009
1 commit
-
If the following sequence of events occurs, then
TREE_PREEMPT_RCU will hang waiting for a grace period to
complete, eventually OOMing the system:o A TREE_PREEMPT_RCU build of the kernel is booted on a system
with more than 64 physical CPUs present (32 on a 32-bit system).
Alternatively, a TREE_PREEMPT_RCU build of the kernel is booted
with RCU_FANOUT set to a sufficiently small value that the
physical CPUs populate two or more leaf rcu_node structures.o A task is preempted in an RCU read-side critical section
while running on a CPU corresponding to a given leaf rcu_node
structure.o All CPUs corresponding to this same leaf rcu_node structure
record quiescent states for the current grace period.o All of these same CPUs go offline (hence the need for enough
physical CPUs to populate more than one leaf rcu_node structure).
This causes the preempted task to be moved to the root rcu_node
structure.At this point, there is nothing left to cause the quiescent
state to be propagated up the rcu_node tree, so the current
grace period never completes.The simplest fix, especially after considering the deadlock
possibilities, is to detect this situation when the last CPU is
offlined, and to set that CPU's ->qsmask bit in its leaf
rcu_node structure. This will cause the next invocation of
force_quiescent_state() to end the grace period.Without this fix, this hang can be triggered in an hour or so on
some machines with rcutorture and random CPU onlining/offlining.
With this fix, these same machines pass a full 10 hours of this
sort of abuse.Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar
15 Oct, 2009
1 commit
-
As the number of callbacks on a given CPU rises, invoke
force_quiescent_state() only every blimit number of callbacks
(defaults to 10,000), and even then only if no other CPU has
invoked force_quiescent_state() in the meantime.This should fix the performance regression reported by Nick.
Reported-by: Nick Piggin
Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
Cc: jens.axboe@oracle.com
LKML-Reference:
Signed-off-by: Ingo Molnar
07 Oct, 2009
3 commits
-
Before this patch, all of the rcu_node structures were in the same lockdep
class, so that lockdep would complain when rcu_preempt_offline_tasks()
acquired the root rcu_node structure's lock while holding one of the leaf
rcu_nodes' locks.This patch changes rcu_init_one() to use a separate
spin_lock_init() for the root rcu_node structure's lock than is
used for that of all of the rest of the rcu_node structures, which
puts the root rcu_node structure's lock in its own lockdep class.Suggested-by: Peter Zijlstra
Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar -
The current interaction between RCU and CPU hotplug requires that
RCU block in CPU notifiers waiting for callbacks to drain.This can be greatly simplified by having each CPU relinquish its
own callbacks, and for both _rcu_barrier() and CPU_DEAD notifiers
to adopt all callbacks that were previously relinquished.This change also eliminates the possibility of certain types of
hangs due to the previous practice of waiting for callbacks to be
invoked from within CPU notifiers. If you don't every wait, you
cannot hang.Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar -
Move the existing rcu_barrier() implementation to rcutree.c,
consistent with the fact that the rcu_barrier() implementation is
tied quite tightly to the RCU implementation.This opens the way to simplify and fix rcutree.c's rcu_barrier()
implementation in a later patch.Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar
06 Oct, 2009
3 commits
-
These issues identified during an old-fashioned face-to-face code
review extending over many hours. This group improves an existing
abstraction and introduces two new ones. It also fixes an RCU
stall-warning bug found while making the other changes.o Make RCU_INIT_FLAVOR() declare its own variables, removing
the need to declare them at each call site.o Create an rcu_for_each_leaf() macro that scans the leaf
nodes of the rcu_node tree.o Create an rcu_for_each_node_breadth_first() macro that does
a breadth-first traversal of the rcu_node tree, AKA
stepping through the array in index-number order.o If all CPUs corresponding to a given leaf rcu_node
structure go offline, then any tasks queued on that leaf
will be moved to the root rcu_node structure. Therefore,
the stall-warning code must dump out tasks queued on the
root rcu_node structure as well as those queued on the leaf
rcu_node structures.Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar -
Whitespace fixes, updated comments, and trivial code movement.
o Fix whitespace error in RCU_HEAD_INIT()
o Move "So where is rcu_write_lock()" comment so that it does
not come between the rcu_read_unlock() header comment and
the rcu_read_unlock() definition.o Move the module_param statements for blimit, qhimark, and
qlowmark to immediately follow the corresponding
definitions.o In __rcu_offline_cpu(), move the assignment to rdp_me
inside the "if" statement, given that rdp_me is not used
outside of that "if" statement.Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar -
Move the rcu_lock_map definition from rcutree.c to rcupdate.c so that
TINY_RCU can use lockdep.Reported-by: Ingo Molnar
Signed-off-by: Paul E. McKenney
Signed-off-by: Ingo Molnar
24 Sep, 2009
3 commits
-
Move declarations and update storage classes to make checkpatch happy.
Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar -
These issues identified during an old-fashioned face-to-face code
review extending over many hours.o Add comments for tricky parts of code, and correct comments
that have passed their sell-by date.o Get rid of the vestiges of rcu_init_sched(), which is no
longer needed now that PREEMPT_RCU is gone.o Move the #include of rcutree_plugin.h to the end of
rcutree.c, which means that, rather than having a random
collection of forward declarations, the new set of forward
declarations document the set of plugins. The new home for
this #include also allows __rcu_init_preempt() to move into
rcutree_plugin.h.o Fix rcu_preempt_check_callbacks() to be static.
Suggested-by: Josh Triplett
Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar
Peter Zijlstra -
These issues identified during an old-fashioned face-to-face code
review extended over many hours.o Bury various forms of the "rsp->completed == rsp->gpnum"
comparison into an rcu_gp_in_progress() function, which has
the beneficial side-effect of forcing consistent use of
ACCESS_ONCE().o Replace hand-coded arithmetic with DIV_ROUND_UP().
o Bury several "!list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x01])"
instances into an rcu_preempted_readers() function, as this
expression indicates that there are no readers blocked
within RCU read-side critical sections blocking the current
grace period. (Though there might well be similar readers
blocking the next grace period.)o Remove a dangling rcu_restart_cpu() declaration that has
been dangling for almost 20 minor releases of the kernel.Signed-off-by: Paul E. McKenney
Acked-by: Peter Zijlstra
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference:
Signed-off-by: Ingo Molnar
19 Sep, 2009
4 commits
-
Fix a number of whitespace ^Ierrors in the include/linux/rcu*
and the kernel/rcu* files.Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
LKML-Reference:
[ did more checkpatch fixlets ]
Signed-off-by: Ingo Molnar -
Commit de078d8 ("rcu: Need to update rnp->gpnum if preemptable RCU
is to be reliable") repeatedly and incorrectly initializes the root
rcu_node structure's ->gpnum field rather than initializing the
->gpnum field of each node in the tree. Fix this. Also add an
additional consistency check to catch this in the future.Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
LKML-Reference:
Signed-off-by: Ingo Molnar -
o Drop the calls to cpu_quiet() from the online/offline code.
These are unnecessary, since force_quiescent_state() will
clean up, and removing them simplifies the code a bit.o Add a warning to check that we don't enqueue the same blocked
task twice onto the ->blocked_tasks[] lists.o Rework the phase computation in rcu_preempt_note_context_switch()
to be more readable, as suggested by Josh Triplett.o Disable irqs to close a race between the scheduling clock
interrupt and rcu_preempt_note_context_switch() WRT the
->rcu_read_unlock_special field.o Add comments to rnp->lock acquisition and release within
rcu_read_unlock_special() noting that irqs are already
disabled.Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
LKML-Reference:
Signed-off-by: Ingo Molnar -
o Verify that qsmask bits stay clear through GP
initialization.o Verify that cpu_quiet_msk_finish() is never invoked unless
there actually is an RCU grace period in progress.o Verify that all internal-node rcu_node structures have empty
blocked_tasks[] lists.o Verify that child rcu_node structure's bits remain clear after
acquiring parent's lock.Signed-off-by: Paul E. McKenney
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
LKML-Reference:
Signed-off-by: Ingo Molnar