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Introduce stop_machine_create/destroy. With this interface subsystems
that need a non-failing stop_machine environment can create the
stop_machine machine threads before actually calling stop_machine.
When the threads aren't needed anymore they can be killed with
stop_machine_destroy again.
When stop_machine gets called and the threads aren't present they
will be created and destroyed automatically. This restores the old
behaviour of stop_machine.
This patch also converts cpu hotplug to the new interface since it
is special: cpu_down calls __stop_machine instead of stop_machine.
However the kstop threads will only be created when stop_machine
gets called.
Changing the code so that the threads would be created automatically
on __stop_machine is currently not possible: when __stop_machine gets
called we hold cpu_add_remove_lock, which is the same lock that
create_rt_workqueue would take. So the workqueue needs to be created
before the cpu hotplug code locks cpu_add_remove_lock.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
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Impact: Reduce stack usage, use new cpumask API.
Mainly changing cpumask_t to 'struct cpumask' and similar simple API
conversion. Two conversions worth mentioning:
1) we use cpumask_any_but to avoid a temporary in kernel/softlockup.c,
2) Use cpumask_var_t in taskstats_user_cmd().
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Mike Travis <travis@sgi.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@redhat.com>
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Everyone should be using stop_machine() now. The staged API
transition helped life in linux-next.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
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Instead of a "cpu" arg with magic values NR_CPUS (any cpu) and ~0 (all
cpus), pass a cpumask_t. Allow NULL for the common case (where we
don't care which CPU the function is run on): temporary cpumask_t's
are usually considered bad for stack space.
This deprecates stop_machine_run, to be removed soon when all the
callers are dead.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
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stop_machine creates a kthread which creates kernel threads. We can
create those threads directly and simplify things a little. Some care
must be taken with CPU hotunplug, which has special needs, but that code
seems more robust than it was in the past.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
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-allow stop_mahcine_run() to call a function on all cpus. Calling
stop_machine_run() with a 'ALL_CPUS' invokes this new behavior.
stop_machine_run() proceeds as normal until the calling cpu has
invoked 'fn'. Then, we tell all the other cpus to call 'fn'.
Signed-off-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
CC: Adrian Bunk <bunk@stusta.de>
CC: Andi Kleen <andi@firstfloor.org>
CC: Alexey Dobriyan <adobriyan@gmail.com>
CC: Christoph Hellwig <hch@infradead.org>
CC: mingo@elte.hu
CC: akpm@osdl.org
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Signed-off-by: David Woodhouse <dwmw2@infradead.org>
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The attached patch fixes a race between kallsyms and insmod/rmmod.
The problem is this:
(1) The various kallsyms functions poke around in the module list without any
locking so that they can be called from the oops handler.
(2) Although insmod and rmmod use locks to exclude each other, these have no
effect on the kallsyms function.
(3) Although rmmod modifies the module state with the machine "stopped", it
hasn't removed the metadata from the module metadata list, meaning that
as soon as the machine is "restarted", the metadata can be observed by
kallsyms.
It's not possible to say that an item in that list should be ignored if
it's state is marked as inactive - you can't get at the state information
because you can't trust the metadata in which it is embedded.
Furthermore, list linkage information is embedded in the metadata too, so
you can't trust that either...
(4) kallsyms may be walking the module list without a lock whilst either
insmod or rmmod are busy changing it. insmod probably isn't a problem
since nothing is going a way, but rmmod is as it's deleting an entry.
(5) Therefore nothing that uses these functions can in any way trust any
pointers to "static" data (such as module symbol names or module names)
that are returned.
(6) On ppc64 the problems are exacerbated since the hypervisor may reschedule
bits of the kernel, making operations that appear adjacent occur a long
time apart.
This patch fixes the race by only linking/unlinking modules into/from the
master module list with the machine in the "stopped" state. This means that
any "static" information can be trusted as far as the next kernel reschedule
on any given CPU without the need to hold any locks.
However, I'm not sure how this is affected by preemption. I suspect more work
may need to be done in that case, but I'm not entirely sure.
This also means that rmmod has to bump the machine into the stopped state
twice... but since that shouldn't be a common operation, I don't think that's
a problem.
I've amended this patch to not get spinlocks whilst in the machine locked
state - there's no point as nothing else can be holding spinlocks.
Signed-Off-By: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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The "bogolock" code was introduced in module.c, as a way of freezing
the machine when we wanted to remove a module. This patch moves it
out to stop_machine.c and stop_machine.h.
Since the code changes affinity and proirity, it's impolite to hijack
the current context, so we use a kthread. This means we have to pass
the function rather than implement "stop_machine()" and
"restart_machine()".
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