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guts of saved_sigmask-based sigsuspend/rt_sigsuspend. Takes
kernel sigset_t *.
Open-coded instances replaced with calling it.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull smp hotplug cleanups from Thomas Gleixner:
"This series is merily a cleanup of code copied around in arch/* and
not changing any of the real cpu hotplug horrors yet. I wish I'd had
something more substantial for 3.5, but I underestimated the lurking
horror..."
Fix up trivial conflicts in arch/{arm,sparc,x86}/Kconfig and
arch/sparc/include/asm/thread_info_32.h
* 'smp-hotplug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (79 commits)
um: Remove leftover declaration of alloc_task_struct_node()
task_allocator: Use config switches instead of magic defines
sparc: Use common threadinfo allocator
score: Use common threadinfo allocator
sh-use-common-threadinfo-allocator
mn10300: Use common threadinfo allocator
powerpc: Use common threadinfo allocator
mips: Use common threadinfo allocator
hexagon: Use common threadinfo allocator
m32r: Use common threadinfo allocator
frv: Use common threadinfo allocator
cris: Use common threadinfo allocator
x86: Use common threadinfo allocator
c6x: Use common threadinfo allocator
fork: Provide kmemcache based thread_info allocator
tile: Use common threadinfo allocator
fork: Provide weak arch_release_[task_struct|thread_info] functions
fork: Move thread info gfp flags to header
fork: Remove the weak insanity
sh: Remove cpu_idle_wait()
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Replace __HAVE_ARCH_TASK_ALLOCATOR and __HAVE_ARCH_THREAD_ALLOCATOR
with proper config switches.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Tony Luck <tony.luck@intel.com>
Link: http://lkml.kernel.org/r/20120505150142.371309416@linutronix.de
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Several architectures have their own kmemcache based thread allocator
because THREAD_SIZE is smaller than PAGE_SIZE. Add it to the core code
conditionally on THREAD_SIZE < PAGE_SIZE so the private copies can go.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20120505150141.491002124@linutronix.de
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Reason: Pull in the separate branch which was created so arch/tile can
base further work on it.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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These functions allow us to move most of the duplicated thread_info
allocators to the core code.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20120505150141.366461660@linutronix.de
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These flags can be useful for extra allocations outside of the core
code.
Add __GFP_NOTRACK to them, so the archs which have kmemcheck do
not have to provide extra allocators just for that reason.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20120505150141.428211694@linutronix.de
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We error out when compiling with gcc4.1.[01] as it miscompiles
__weak. The workaround with magic defines is not longer
necessary. Make it __weak again.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20120505150141.306358267@linutronix.de
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Will replace the misnomed cpu_idle_wait() function which is copied a
gazillion times all over arch/*
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20120507175652.049316594@linutronix.de
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All archs define init_task in the same way (except ia64, but there is
no particular reason why ia64 cannot use the common version). Create a
generic instance so all archs can be converted over.
The config switch is temporary and will be removed when all archs are
converted over.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Chen Liqin <liqin.chen@sunplusct.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Chris Zankel <chris@zankel.net>
Cc: David Howells <dhowells@redhat.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Guan Xuetao <gxt@mprc.pku.edu.cn>
Cc: Haavard Skinnemoen <hskinnemoen@gmail.com>
Cc: Hirokazu Takata <takata@linux-m32r.org>
Cc: James E.J. Bottomley <jejb@parisc-linux.org>
Cc: Jesper Nilsson <jesper.nilsson@axis.com>
Cc: Jonas Bonn <jonas@southpole.se>
Cc: Mark Salter <msalter@redhat.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Mike Frysinger <vapier@gentoo.org>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Richard Kuo <rkuo@codeaurora.org>
Cc: Richard Weinberger <richard@nod.at>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Link: http://lkml.kernel.org/r/20120503085034.092585287@linutronix.de
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idle_thread_init() does not have arguments.
Reported-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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percpu areas are already allocated during boot for each possible cpu.
percpu idle threads can be considered as an extension of the percpu areas,
and allocate them for each possible cpu during boot.
This will eliminate the need for workqueue based idle thread allocation.
In future we can move the idle thread area into the percpu area too.
[ tglx: Moved the loop into smpboot.c and added an error check when
the init code failed to allocate an idle thread for a cpu which
should be onlined ]
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: venki@google.com
Link: http://lkml.kernel.org/r/1334966930.28674.245.camel@sbsiddha-desk.sc.intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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All SMP architectures have magic to fork the idle task and to store it
for reusage when cpu hotplug is enabled. Provide a generic
infrastructure for it.
Create/reinit the idle thread for the cpu which is brought up in the
generic code and hand the thread pointer to the architecture code via
__cpu_up().
Note, that fork_idle() is called via a workqueue, because this
guarantees that the idle thread does not get a reference to a user
space VM. This can happen when the boot process did not bring up all
possible cpus and a later cpu_up() is initiated via the sysfs
interface. In that case fork_idle() would be called in the context of
the user space task and take a reference on the user space VM.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Mike Frysinger <vapier@gentoo.org>
Cc: Jesper Nilsson <jesper.nilsson@axis.com>
Cc: Richard Kuo <rkuo@codeaurora.org>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Hirokazu Takata <takata@linux-m32r.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: David Howells <dhowells@redhat.com>
Cc: James E.J. Bottomley <jejb@parisc-linux.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: x86@kernel.org
Acked-by: Venkatesh Pallipadi <venki@google.com>
Link: http://lkml.kernel.org/r/20120420124557.102478630@linutronix.de
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Start a new file, which will hold SMP and CPU hotplug related generic
infrastructure.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Mike Frysinger <vapier@gentoo.org>
Cc: Jesper Nilsson <jesper.nilsson@axis.com>
Cc: Richard Kuo <rkuo@codeaurora.org>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Hirokazu Takata <takata@linux-m32r.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: David Howells <dhowells@redhat.com>
Cc: James E.J. Bottomley <jejb@parisc-linux.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: x86@kernel.org
Link: http://lkml.kernel.org/r/20120420124557.035417523@linutronix.de
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Preparatory patch to make the idle thread allocation for secondary
cpus generic.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Mike Frysinger <vapier@gentoo.org>
Cc: Jesper Nilsson <jesper.nilsson@axis.com>
Cc: Richard Kuo <rkuo@codeaurora.org>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Hirokazu Takata <takata@linux-m32r.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: David Howells <dhowells@redhat.com>
Cc: James E.J. Bottomley <jejb@parisc-linux.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: x86@kernel.org
Link: http://lkml.kernel.org/r/20120420124556.964170564@linutronix.de
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull RCU changes from Ingo Molnar:
"This is the v3.5 RCU tree from Paul E. McKenney:
1) A set of improvements and fixes to the RCU_FAST_NO_HZ feature (with
more on the way for 3.6). Posted to LKML:
https://lkml.org/lkml/2012/4/23/324 (commits 1-3 and 5),
https://lkml.org/lkml/2012/4/16/611 (commit 4),
https://lkml.org/lkml/2012/4/30/390 (commit 6), and
https://lkml.org/lkml/2012/5/4/410 (commit 7, combined with
the other commits for the convenience of the tester).
2) Changes to make rcu_barrier() avoid disrupting execution of CPUs
that have no RCU callbacks. Posted to LKML:
https://lkml.org/lkml/2012/4/23/322.
3) A couple of commits that improve the efficiency of the interaction
between preemptible RCU and the scheduler, these two being all that
survived an abortive attempt to allow preemptible RCU's
__rcu_read_lock() to be inlined. The full set was posted to LKML at
https://lkml.org/lkml/2012/4/14/143, and the first and third patches
of that set remain.
4) Lai Jiangshan's algorithmic implementation of SRCU, which includes
call_srcu() and srcu_barrier(). A major feature of this new
implementation is that synchronize_srcu() no longer disturbs the
execution of other CPUs. This work is based on earlier
implementations by Peter Zijlstra and Paul E. McKenney. Posted to
LKML: https://lkml.org/lkml/2012/2/22/82.
5) A number of miscellaneous bug fixes and improvements which were
posted to LKML at: https://lkml.org/lkml/2012/4/23/353 with
subsequent updates posted to LKML."
* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (32 commits)
rcu: Make rcu_barrier() less disruptive
rcu: Explicitly initialize RCU_FAST_NO_HZ per-CPU variables
rcu: Make RCU_FAST_NO_HZ handle timer migration
rcu: Update RCU maintainership
rcu: Make exit_rcu() more precise and consolidate
rcu: Move PREEMPT_RCU preemption to switch_to() invocation
rcu: Ensure that RCU_FAST_NO_HZ timers expire on correct CPU
rcu: Add rcutorture test for call_srcu()
rcu: Implement per-domain single-threaded call_srcu() state machine
rcu: Use single value to handle expedited SRCU grace periods
rcu: Improve srcu_readers_active_idx()'s cache locality
rcu: Remove unused srcu_barrier()
rcu: Implement a variant of Peter's SRCU algorithm
rcu: Improve SRCU's wait_idx() comments
rcu: Flip ->completed only once per SRCU grace period
rcu: Increment upper bit only for srcu_read_lock()
rcu: Remove fast check path from __synchronize_srcu()
rcu: Direct algorithmic SRCU implementation
rcu: Introduce rcutorture testing for rcu_barrier()
timer: Fix mod_timer_pinned() header comment
...
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git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/rcu
Pull the v3.5 RCU tree from Paul E. McKenney:
1) A set of improvements and fixes to the RCU_FAST_NO_HZ feature
(with more on the way for 3.6). Posted to LKML:
https://lkml.org/lkml/2012/4/23/324 (commits 1-3 and 5),
https://lkml.org/lkml/2012/4/16/611 (commit 4),
https://lkml.org/lkml/2012/4/30/390 (commit 6), and
https://lkml.org/lkml/2012/5/4/410 (commit 7, combined with
the other commits for the convenience of the tester).
2) Changes to make rcu_barrier() avoid disrupting execution of CPUs
that have no RCU callbacks. Posted to LKML:
https://lkml.org/lkml/2012/4/23/322.
3) A couple of commits that improve the efficiency of the interaction
between preemptible RCU and the scheduler, these two being all
that survived an abortive attempt to allow preemptible RCU's
__rcu_read_lock() to be inlined. The full set was posted to
LKML at https://lkml.org/lkml/2012/4/14/143, and the first and
third patches of that set remain.
4) Lai Jiangshan's algorithmic implementation of SRCU, which includes
call_srcu() and srcu_barrier(). A major feature of this new
implementation is that synchronize_srcu() no longer disturbs
the execution of other CPUs. This work is based on earlier
implementations by Peter Zijlstra and Paul E. McKenney. Posted to
LKML: https://lkml.org/lkml/2012/2/22/82.
5) A number of miscellaneous bug fixes and improvements which were
posted to LKML at: https://lkml.org/lkml/2012/4/23/353 with
subsequent updates posted to LKML.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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'inline.2012.05.02b' and 'srcu.2012.05.07b' into HEAD
barrier: Reduce the amount of disturbance by rcu_barrier() to the rest of
the system. This branch also includes improvements to
RCU_FAST_NO_HZ, which are included here due to conflicts.
fixes: Miscellaneous fixes.
inline: Remaining changes from an abortive attempt to inline
preemptible RCU's __rcu_read_lock(). These are (1) making
exit_rcu() avoid unnecessary work and (2) avoiding having
preemptible RCU record a blocked thread when the scheduler
declines to do a context switch.
srcu: Lai Jiangshan's algorithmic implementation of SRCU, including
call_srcu().
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Add srcu_torture_deferred_free() for srcu_ops so as to test the new
call_srcu(). Rename the original srcu_ops to srcu_sync_ops.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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This commit implements an SRCU state machine in support of call_srcu().
The state machine is preemptible, light-weight, and single-threaded,
minimizing synchronization overhead. In particular, there is no longer
any need for synchronize_srcu() to be guarded by a mutex.
Expedited processing is handled, at least in the absence of concurrent
grace-period operations on that same srcu_struct structure, by having
the synchronize_srcu_expedited() thread take on the role of the
workqueue thread for one iteration.
There is a reasonable probability that a given SRCU callback will
be invoked on the same CPU that registered it, however, there is no
guarantee. Concurrent SRCU grace-period primitives can cause callbacks
to be executed elsewhere, even in absence of CPU-hotplug operations.
Callbacks execute in process context, but under the influence of
local_bh_disable(), so it is illegal to sleep in an SRCU callback
function.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The earlier algorithm used an "expedited" flag combined with a "trycount"
counter to differentiate between normal and expedited SRCU grace periods.
However, the difference can be encoded into a single counter with a cutoff
value and different initial values for expedited and normal SRCU grace
periods. This commit makes that change.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Conflicts:
kernel/srcu.c
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Expand the calls to srcu_readers_active_idx() from srcu_readers_active()
inline. This change improves cache locality by interating over the CPUs
once rather than twice.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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This commit implements a variant of Peter's algorithm, which may be found
at https://lkml.org/lkml/2012/2/1/119.
o Make the checking lock-free to enable parallel checking.
Parallel checking is required when (1) the original checking
task is preempted for a long time, (2) sychronize_srcu_expedited()
starts during an ongoing SRCU grace period, or (3) we wish to
avoid acquiring a lock.
o Since the checking is lock-free, we avoid a mutex in state machine
for call_srcu().
o Remove the SRCU_REF_MASK and remove the coupling with the flipping.
This might allow us to remove the preempt_disable() in future
versions, though such removal will need great care because it
rescinds the one-old-reader-per-CPU guarantee.
o Remove a smp_mb(), simplify the comments and make the smp_mb() pairs
more intuitive.
Inspired-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The safety of SRCU is provided byy wait_idx() rather than flipping.
The flipping actually prevents starvation.
This commit therefore updates the comments to more accurately and
precisely describe what is going on.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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This is an optimization of the SRCU grace period. To guard against
preempted readers with old values of the counter, it suffices to scan the
old counters once more, then flip ->completed only one time. The reason
this works is that the old readers must have incremented the old set of
counters (if they have not yet incremented, then their critical section
starts after this grace period, so they may be safely ignored).
This commit therefore optimizes the second flip out in favor of a simple
rescan.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The purpose of the upper bit of SRCU's per-CPU counters is to guarantee
that no reasonable series of srcu_read_lock() and srcu_read_unlock()
operations can return the value of the counter to its original value.
This guarantee is require only after the index has been switched to
the other set of counters, so at most one srcu_read_lock() can affect
a given CPU's counter. The number of srcu_read_unlock() operations
on a given counter is limited to the number of tasks in the system,
which given the Linux kernel's current structure is limited to far less
than 2^30 on 32-bit systems and far less than 2^62 on 64-bit systems.
(Something about a limited number of bytes in the kernel's address space.)
Therefore, if srcu_read_lock() increments the upper bits, then
srcu_read_unlock() need not do so. In this case, an srcu_read_lock() and
an srcu_read_unlock() will flip the lower bit of the upper field of the
counter. An unreasonably large additional number of srcu_read_unlock()
operations would be required to return the counter to its initial value,
thus preserving the guarantee.
This commit takes this approach, which further allows it to shrink
the size of the upper field to one bit, making the number of
srcu_read_unlock() operations required to return the counter to its
initial value even more unreasonable than before.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The fastpath in __synchronize_srcu() is designed to handle cases where
there are a large number of concurrent calls for the same srcu_struct
structure. However, the Linux kernel currently does not use SRCU in
this manner, so remove the fastpath checks for simplicity.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The current implementation of synchronize_srcu_expedited() can cause
severe OS jitter due to its use of synchronize_sched(), which in turn
invokes try_stop_cpus(), which causes each CPU to be sent an IPI.
This can result in severe performance degradation for real-time workloads
and especially for short-interation-length HPC workloads. Furthermore,
because only one instance of try_stop_cpus() can be making forward progress
at a given time, only one instance of synchronize_srcu_expedited() can
make forward progress at a time, even if they are all operating on
distinct srcu_struct structures.
This commit, inspired by an earlier implementation by Peter Zijlstra
(https://lkml.org/lkml/2012/1/31/211) and by further offline discussions,
takes a strictly algorithmic bits-in-memory approach. This has the
disadvantage of requiring one explicit memory-barrier instruction in
each of srcu_read_lock() and srcu_read_unlock(), but on the other hand
completely dispenses with OS jitter and furthermore allows SRCU to be
used freely by CPUs that RCU believes to be idle or offline.
The update-side implementation handles the single read-side memory
barrier by rechecking the per-CPU counters after summing them and
by running through the update-side state machine twice.
This implementation has passed moderate rcutorture testing on both
x86 and Power. Also updated to use this_cpu_ptr() instead of per_cpu_ptr(),
as suggested by Peter Zijlstra.
Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
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Although rcutorture does invoke rcu_barrier() and friends, it cannot
really be called a torture test given that it invokes them only once
at the end of the test. This commit therefore introduces heavy-duty
rcutorture testing for rcu_barrier(), which may be carried out
concurrently with normal rcutorture testing.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The rcutorture initialization code ignored the error returns from
rcu_torture_onoff_init() and rcu_torture_stall_init(). The rcutorture
cleanup code failed to NULL out a number of pointers. These bugs will
normally have no effect, but this commit fixes them nevertheless.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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When running preemptible RCU, if a task exits in an RCU read-side
critical section having blocked within that same RCU read-side critical
section, the task must be removed from the list of tasks blocking a
grace period (perhaps the current grace period, perhaps the next grace
period, depending on timing). The exit() path invokes exit_rcu() to
do this cleanup.
However, the current implementation of exit_rcu() needlessly does the
cleanup even if the task did not block within the current RCU read-side
critical section, which wastes time and needlessly increases the size
of the state space. Fix this by only doing the cleanup if the current
task is actually on the list of tasks blocking some grace period.
While we are at it, consolidate the two identical exit_rcu() functions
into a single function.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Linus Torvalds <torvalds@linux-foundation.org>
Conflicts:
kernel/rcupdate.c
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Currently, PREEMPT_RCU readers are enqueued upon entry to the scheduler.
This is inefficient because enqueuing is required only if there is a
context switch, and entry to the scheduler does not guarantee a context
switch.
The commit therefore moves the enqueuing to immediately precede the
call to switch_to() from the scheduler.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Linus Torvalds <torvalds@linux-foundation.org>
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The mod_timer_pinned() header comment states that it prevents timers
from being migrated to a different CPU. This is not the case, instead,
it ensures that the timer is posted to the current CPU, but does nothing
to prevent CPU-hotplug operations from migrating the timer.
This commit therefore brings the comment header into alignment with
reality.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
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The rcu_blocking_is_gp() function tests to see if there is only one
online CPU, and if so, synchronize_sched() and friends become no-ops.
However, for larger systems, num_online_cpus() scans a large vector,
and might be preempted while doing so. While preempted, any number
of CPUs might come online and go offline, potentially resulting in
num_online_cpus() returning 1 when there never had only been one
CPU online. This could result in a too-short RCU grace period, which
could in turn result in total failure, except that the only way that
the grace period is too short is if there is an RCU read-side critical
section spanning it. For RCU-sched and RCU-bh (which are the only
cases using rcu_blocking_is_gp()), RCU read-side critical sections
have either preemption or bh disabled, which prevents CPUs from going
offline. This in turn prevents actual failures from occurring.
This commit therefore adds a large block comment to rcu_blocking_is_gp()
documenting why it is safe. This commit also moves rcu_blocking_is_gp()
into kernel/rcutree.c, which should help prevent unwary developers from
mistaking it for a generally useful function.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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Commit #0209f649 (rcu: limit rcu_node leaf-level fanout) set an upper
limit of 16 on the leaf-level fanout for the rcu_node tree. This was
needed to reduce lock contention that was induced by the synchronization
of scheduling-clock interrupts, which was in turn needed to improve
energy efficiency for moderate-sized lightly loaded servers.
However, reducing the leaf-level fanout means that there are more
leaf-level rcu_node structures in the tree, which in turn means that
RCU's grace-period initialization incurs more cache misses. This is
not a problem on moderate-sized servers with only a few tens of CPUs,
but becomes a major source of real-time latency spikes on systems with
many hundreds of CPUs. In addition, the workloads running on these large
systems tend to be CPU-bound, which eliminates the energy-efficiency
advantages of synchronizing scheduling-clock interrupts. Therefore,
these systems need maximal values for the rcu_node leaf-level fanout.
This commit addresses this problem by introducing a new kernel parameter
named RCU_FANOUT_LEAF that directly controls the leaf-level fanout.
This parameter defaults to 16 to handle the common case of a moderate
sized lightly loaded servers, but may be set higher on larger systems.
Reported-by: Mike Galbraith <efault@gmx.de>
Reported-by: Dimitri Sivanich <sivanich@sgi.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The rcu_barrier() primitive interrupts each and every CPU, registering
a callback on every CPU. Once all of these callbacks have been invoked,
rcu_barrier() knows that every callback that was registered before
the call to rcu_barrier() has also been invoked.
However, there is no point in registering a callback on a CPU that
currently has no callbacks, most especially if that CPU is in a
deep idle state. This commit therefore makes rcu_barrier() avoid
interrupting CPUs that have no callbacks. Doing this requires reworking
the handling of orphaned callbacks, otherwise callbacks could slip through
rcu_barrier()'s net by being orphaned from a CPU that rcu_barrier() had
not yet interrupted to a CPU that rcu_barrier() had already interrupted.
This reworking was needed anyway to take a first step towards weaning
RCU from the CPU_DYING notifier's use of stop_cpu().
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The current initialization of the RCU_FAST_NO_HZ per-CPU variables makes
needless and fragile assumptions about the initial value of things like
the jiffies counter. This commit therefore explicitly initializes all of
them that are better started with a non-zero value. It also adds some
comments describing the per-CPU state variables.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The current RCU_FAST_NO_HZ assumes that timers do not migrate unless a
CPU goes offline, in which case it assumes that the CPU will have to come
out of dyntick-idle mode (cancelling the timer) in order to go offline.
This is important because when RCU_FAST_NO_HZ permits a CPU to enter
dyntick-idle mode despite having RCU callbacks pending, it posts a timer
on that CPU to force a wakeup on that CPU. This wakeup ensures that the
CPU will eventually handle the end of the grace period, including invoking
its RCU callbacks.
However, Pascal Chapperon's test setup shows that the timer handler
rcu_idle_gp_timer_func() really does get invoked in some cases. This is
problematic because this can cause the CPU that entered dyntick-idle
mode despite still having RCU callbacks pending to remain in
dyntick-idle mode indefinitely, which means that its RCU callbacks might
never be invoked. This situation can result in grace-period delays or
even system hangs, which matches Pascal's observations of slow boot-up
and shutdown (https://lkml.org/lkml/2012/4/5/142). See also the bugzilla:
https://bugzilla.redhat.com/show_bug.cgi?id=806548
This commit therefore causes the "should never be invoked" timer handler
rcu_idle_gp_timer_func() to use smp_call_function_single() to wake up
the CPU for which the timer was intended, allowing that CPU to invoke
its RCU callbacks in a timely manner.
Reported-by: Pascal Chapperon <pascal.chapperon@wanadoo.fr>
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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Timers are subject to migration, which can lead to the following
system-hang scenario when CONFIG_RCU_FAST_NO_HZ=y:
1. CPU 0 executes synchronize_rcu(), which posts an RCU callback.
2. CPU 0 then goes idle. It cannot immediately invoke the callback,
but there is nothing RCU needs from ti, so it enters dyntick-idle
mode after posting a timer.
3. The timer gets migrated to CPU 1.
4. CPU 0 never wakes up, so the synchronize_rcu() never returns, so
the system hangs.
This commit fixes this problem by using mod_timer_pinned(), as suggested
by Peter Zijlstra, to ensure that the timer is actually posted on the
running CPU.
Reported-by: Dipankar Sarma <dipankar@in.ibm.com>
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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RCU_FAST_NO_HZ uses a timer to limit the time that a CPU with callbacks
can remain in dyntick-idle mode. This timer is cancelled when the CPU
exits idle, and therefore should never fire. However, if the timer
were migrated to some other CPU for whatever reason (1) the timer could
actually fire and (2) firing on some other CPU would fail to wake up the
CPU with callbacks, possibly resulting in sluggishness or a system hang.
This commit therfore adds a WARN_ON_ONCE() to the timer handler in order
to detect this condition.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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Both Steven Rostedt's new idle-capable trace macros and the RCU_NONIDLE()
macro can cause RCU to momentarily pause out of idle without the rest
of the system being involved. This can cause rcu_prepare_for_idle()
to run through its state machine too quickly, which can in turn result
in needless scheduling-clock interrupts.
This commit therefore adds code to enable rcu_prepare_for_idle() to
distinguish between an initial entry to idle on the one hand (which needs
to advance the rcu_prepare_for_idle() state machine) and an idle reentry
due to idle-capable trace macros and RCU_NONIDLE() on the other hand
(which should avoid advancing the rcu_prepare_for_idle() state machine).
Additional state is maintained to allow the timer to be correctly reposted
when returning after a momentary pause out of idle, and even more state
is maintained to detect when new non-lazy callbacks have been enqueued
(which may require re-evaluation of the approach to idleness).
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The RCU_FAST_NO_HZ facility uses an hrtimer to wake up a CPU when
it is allowed to go into dyntick-idle mode, which is almost always
cancelled soon after. This is not what hrtimers are good at, so
this commit switches to the timer wheel.
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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Traces of rcu_prep_idle events can be confusing because
rcu_cleanup_after_idle() does no tracing. This commit therefore adds
this tracing.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull core locking updates from Ingo Molnar:
"This update:
- extends and simplifies x86 NMI callback handling code to enhance
and fix the HP hw-watchdog driver
- simplifies the x86 NMI callback handling code to fix a kmemcheck
bug.
- enhances the hung-task debugger"
* 'core-locking-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/nmi: Fix the type of the nmiaction.flags field
x86/nmi: Fix page faults by nmiaction if kmemcheck is enabled
x86/nmi: Add new NMI queues to deal with IO_CHK and SERR
watchdog, hpwdt: Remove priority option for NMI callback
hung task debugging: Inject NMI when hung and going to panic
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Send an NMI to all CPUs when a hung task is detected and the hung
task code is configured to panic. This gives us a fairly uptodate
snapshot of all CPUs in the system.
This lets us get stack trace of all CPUs which makes life easier
trying to debug a deadlock, and the NMI doesn't change anything
since the next step is a kernel panic.
Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/1331848040-1676-1-git-send-email-levinsasha928@gmail.com
[ extended the changelog a bit ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull perf, x86 and scheduler updates from Ingo Molnar.
* 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
tracing: Do not enable function event with enable
perf stat: handle ENXIO error for perf_event_open
perf: Turn off compiler warnings for flex and bison generated files
perf stat: Fix case where guest/host monitoring is not supported by kernel
perf build-id: Fix filename size calculation
* 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86, kvm: KVM paravirt kernels don't check for CPUID being unavailable
x86: Fix section annotation of acpi_map_cpu2node()
x86/microcode: Ensure that module is only loaded on supported Intel CPUs
* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
sched: Fix KVM and ia64 boot crash due to sched_groups circular linked list assumption
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assumption
If we have one cpu that failed to boot and boot cpu gave up on
waiting for it and then another cpu is being booted, kernel
might crash with following OOPS:
BUG: unable to handle kernel NULL pointer dereference at 0000000000000018
IP: [<ffffffff812c3630>] __bitmap_weight+0x30/0x80
Call Trace:
[<ffffffff8108b9b6>] build_sched_domains+0x7b6/0xa50
The crash happens in init_sched_groups_power() that expects
sched_groups to be circular linked list. However it is not
always true, since sched_groups preallocated in __sdt_alloc are
initialized in build_sched_groups and it may exit early
if (cpu != cpumask_first(sched_domain_span(sd)))
return 0;
without initializing sd->groups->next field.
Fix bug by initializing next field right after sched_group was
allocated.
Also-Reported-by: Jiang Liu <liuj97@gmail.com>
Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Cc: a.p.zijlstra@chello.nl
Cc: pjt@google.com
Cc: seto.hidetoshi@jp.fujitsu.com
Link: http://lkml.kernel.org/r/1336559908-32533-1-git-send-email-imammedo@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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With the adding of function tracing event to perf, it caused a
side effect that produces the following warning when enabling all
events in ftrace:
# echo 1 > /sys/kernel/debug/tracing/events/enable
[console]
event trace: Could not enable event function
This is because when enabling all events via the debugfs system
it ignores events that do not have a ->reg() function assigned.
This was to skip over the ftrace internal events (as they are
not TRACE_EVENTs). But as the ftrace function event now has
a ->reg() function attached to it for use with perf, it is no
longer ignored.
Worse yet, this ->reg() function is being called when it should
not be. It returns an error and causes the above warning to
be printed.
By adding a new event_call flag (TRACE_EVENT_FL_IGNORE_ENABLE)
and have all ftrace internel event structures have it set,
setting the events/enable will no longe try to incorrectly enable
the function event and does not warn.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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Export handle_edge_irq() and irq_to_desc() to modules to allow them to
do things such as
__irq_set_handler_locked(...., handle_edge_irq);
This fixes
ERROR: "handle_edge_irq" [drivers/gpio/gpio-pch.ko] undefined!
ERROR: "irq_to_desc" [drivers/gpio/gpio-pch.ko] undefined!
when gpio-pch is being built as a module.
This was introduced by commit df9541a60af0 ("gpio: pch9: Use proper flow
type handlers") that added
__irq_set_handler_locked(d->irq, handle_edge_irq);
but handle_edge_irq() was not exported for modules (and inlined
__irq_set_handler_locked() requires irq_to_desc() exported as well)
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Fork() failure post namespace creation for a child cloned with
CLONE_NEWPID leaks pid_namespace/mnt_cache due to proc being mounted
during creation, but not unmounted during cleanup. Call
pid_ns_release_proc() during cleanup.
Signed-off-by: Mike Galbraith <efault@gmx.de>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Louis Rilling <louis.rilling@kerlabs.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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