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2 changes: 1 addition & 1 deletion CREDITS
Original file line number Diff line number Diff line change
Expand Up @@ -3101,7 +3101,7 @@ S: Minto, NSW, 2566
S: Australia

N: Stephen Smalley
E: sds@epoch.ncsc.mil
E: sds@tycho.nsa.gov
D: portions of the Linux Security Module (LSM) framework and security modules

N: Chris Smith
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25 changes: 14 additions & 11 deletions Documentation/RCU/RTFP.txt
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Expand Up @@ -90,16 +90,20 @@ at OLS. The resulting abundance of RCU patches was presented the
following year [McKenney02a], and use of RCU in dcache was first
described that same year [Linder02a].

Also in 2002, Michael [Michael02b,Michael02a] presented techniques
that defer the destruction of data structures to simplify non-blocking
synchronization (wait-free synchronization, lock-free synchronization,
and obstruction-free synchronization are all examples of non-blocking
synchronization). In particular, this technique eliminates locking,
reduces contention, reduces memory latency for readers, and parallelizes
pipeline stalls and memory latency for writers. However, these
techniques still impose significant read-side overhead in the form of
memory barriers. Researchers at Sun worked along similar lines in the
same timeframe [HerlihyLM02,HerlihyLMS03].
Also in 2002, Michael [Michael02b,Michael02a] presented "hazard-pointer"
techniques that defer the destruction of data structures to simplify
non-blocking synchronization (wait-free synchronization, lock-free
synchronization, and obstruction-free synchronization are all examples of
non-blocking synchronization). In particular, this technique eliminates
locking, reduces contention, reduces memory latency for readers, and
parallelizes pipeline stalls and memory latency for writers. However,
these techniques still impose significant read-side overhead in the
form of memory barriers. Researchers at Sun worked along similar lines
in the same timeframe [HerlihyLM02,HerlihyLMS03]. These techniques
can be thought of as inside-out reference counts, where the count is
represented by the number of hazard pointers referencing a given data
structure (rather than the more conventional counter field within the
data structure itself).

In 2003, the K42 group described how RCU could be used to create
hot-pluggable implementations of operating-system functions. Later that
Expand All @@ -113,7 +117,6 @@ number of operating-system kernels [PaulEdwardMcKenneyPhD], a paper
describing how to make RCU safe for soft-realtime applications [Sarma04c],
and a paper describing SELinux performance with RCU [JamesMorris04b].


2005 has seen further adaptation of RCU to realtime use, permitting
preemption of RCU realtime critical sections [PaulMcKenney05a,
PaulMcKenney05b].
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6 changes: 6 additions & 0 deletions Documentation/RCU/checklist.txt
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Expand Up @@ -177,3 +177,9 @@ over a rather long period of time, but improvements are always welcome!

If you want to wait for some of these other things, you might
instead need to use synchronize_irq() or synchronize_sched().

12. Any lock acquired by an RCU callback must be acquired elsewhere
with irq disabled, e.g., via spin_lock_irqsave(). Failing to
disable irq on a given acquisition of that lock will result in
deadlock as soon as the RCU callback happens to interrupt that
acquisition's critical section.
21 changes: 12 additions & 9 deletions Documentation/RCU/listRCU.txt
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Expand Up @@ -232,7 +232,7 @@ entry does not exist. For this to be helpful, the search function must
return holding the per-entry spinlock, as ipc_lock() does in fact do.

Quick Quiz: Why does the search function need to return holding the
per-entry lock for this deleted-flag technique to be helpful?
per-entry lock for this deleted-flag technique to be helpful?

If the system-call audit module were to ever need to reject stale data,
one way to accomplish this would be to add a "deleted" flag and a "lock"
Expand Down Expand Up @@ -275,8 +275,8 @@ flag under the spinlock as follows:
{
struct audit_entry *e;

/* Do not use the _rcu iterator here, since this is the only
* deletion routine. */
/* Do not need to use the _rcu iterator here, since this
* is the only deletion routine. */
list_for_each_entry(e, list, list) {
if (!audit_compare_rule(rule, &e->rule)) {
spin_lock(&e->lock);
Expand Down Expand Up @@ -304,9 +304,12 @@ function to reject newly deleted data.


Answer to Quick Quiz

If the search function drops the per-entry lock before returning, then
the caller will be processing stale data in any case. If it is really
OK to be processing stale data, then you don't need a "deleted" flag.
If processing stale data really is a problem, then you need to hold the
per-entry lock across all of the code that uses the value looked up.
Why does the search function need to return holding the per-entry
lock for this deleted-flag technique to be helpful?

If the search function drops the per-entry lock before returning,
then the caller will be processing stale data in any case. If it
is really OK to be processing stale data, then you don't need a
"deleted" flag. If processing stale data really is a problem,
then you need to hold the per-entry lock across all of the code
that uses the value that was returned.
5 changes: 5 additions & 0 deletions Documentation/RCU/rcu.txt
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Expand Up @@ -111,6 +111,11 @@ o What are all these files in this directory?

You are reading it!

rcuref.txt

Describes how to combine use of reference counts
with RCU.

whatisRCU.txt

Overview of how the RCU implementation works. Along
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31 changes: 15 additions & 16 deletions Documentation/RCU/rcuref.txt
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@@ -1,7 +1,7 @@
Refcounter design for elements of lists/arrays protected by RCU.
Reference-count design for elements of lists/arrays protected by RCU.

Refcounting on elements of lists which are protected by traditional
reader/writer spinlocks or semaphores are straight forward as in:
Reference counting on elements of lists which are protected by traditional
reader/writer spinlocks or semaphores are straightforward:

1. 2.
add() search_and_reference()
Expand All @@ -28,12 +28,12 @@ release_referenced() delete()
...
}

If this list/array is made lock free using rcu as in changing the
write_lock in add() and delete() to spin_lock and changing read_lock
If this list/array is made lock free using RCU as in changing the
write_lock() in add() and delete() to spin_lock and changing read_lock
in search_and_reference to rcu_read_lock(), the atomic_get in
search_and_reference could potentially hold reference to an element which
has already been deleted from the list/array. atomic_inc_not_zero takes
care of this scenario. search_and_reference should look as;
has already been deleted from the list/array. Use atomic_inc_not_zero()
in this scenario as follows:

1. 2.
add() search_and_reference()
Expand All @@ -51,17 +51,16 @@ add() search_and_reference()
release_referenced() delete()
{ {
... write_lock(&list_lock);
atomic_dec(&el->rc, relfunc) ...
... delete_element
} write_unlock(&list_lock);
...
if (atomic_dec_and_test(&el->rc)) ...
call_rcu(&el->head, el_free); delete_element
... write_unlock(&list_lock);
} ...
if (atomic_dec_and_test(&el->rc))
call_rcu(&el->head, el_free);
...
}

Sometimes, reference to the element need to be obtained in the
update (write) stream. In such cases, atomic_inc_not_zero might be an
overkill since the spinlock serialising list updates are held. atomic_inc
is to be used in such cases.

Sometimes, a reference to the element needs to be obtained in the
update (write) stream. In such cases, atomic_inc_not_zero() might be
overkill, since we hold the update-side spinlock. One might instead
use atomic_inc() in such cases.
29 changes: 17 additions & 12 deletions Documentation/RCU/whatisRCU.txt
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Expand Up @@ -200,10 +200,11 @@ rcu_assign_pointer()
the new value, and also executes any memory-barrier instructions
required for a given CPU architecture.

Perhaps more important, it serves to document which pointers
are protected by RCU. That said, rcu_assign_pointer() is most
frequently used indirectly, via the _rcu list-manipulation
primitives such as list_add_rcu().
Perhaps just as important, it serves to document (1) which
pointers are protected by RCU and (2) the point at which a
given structure becomes accessible to other CPUs. That said,
rcu_assign_pointer() is most frequently used indirectly, via
the _rcu list-manipulation primitives such as list_add_rcu().

rcu_dereference()

Expand Down Expand Up @@ -258,9 +259,11 @@ rcu_dereference()
locking.

As with rcu_assign_pointer(), an important function of
rcu_dereference() is to document which pointers are protected
by RCU. And, again like rcu_assign_pointer(), rcu_dereference()
is typically used indirectly, via the _rcu list-manipulation
rcu_dereference() is to document which pointers are protected by
RCU, in particular, flagging a pointer that is subject to changing
at any time, including immediately after the rcu_dereference().
And, again like rcu_assign_pointer(), rcu_dereference() is
typically used indirectly, via the _rcu list-manipulation
primitives, such as list_for_each_entry_rcu().

The following diagram shows how each API communicates among the
Expand Down Expand Up @@ -327,7 +330,7 @@ for specialized uses, but are relatively uncommon.
3. WHAT ARE SOME EXAMPLE USES OF CORE RCU API?

This section shows a simple use of the core RCU API to protect a
global pointer to a dynamically allocated structure. More typical
global pointer to a dynamically allocated structure. More-typical
uses of RCU may be found in listRCU.txt, arrayRCU.txt, and NMI-RCU.txt.

struct foo {
Expand Down Expand Up @@ -410,6 +413,8 @@ o Use synchronize_rcu() -after- removing a data element from an
data item.

See checklist.txt for additional rules to follow when using RCU.
And again, more-typical uses of RCU may be found in listRCU.txt,
arrayRCU.txt, and NMI-RCU.txt.


4. WHAT IF MY UPDATING THREAD CANNOT BLOCK?
Expand Down Expand Up @@ -513,7 +518,7 @@ production-quality implementation, and see:

for papers describing the Linux kernel RCU implementation. The OLS'01
and OLS'02 papers are a good introduction, and the dissertation provides
more details on the current implementation.
more details on the current implementation as of early 2004.


5A. "TOY" IMPLEMENTATION #1: LOCKING
Expand Down Expand Up @@ -768,7 +773,6 @@ RCU pointer/list traversal:
rcu_dereference
list_for_each_rcu (to be deprecated in favor of
list_for_each_entry_rcu)
list_for_each_safe_rcu (deprecated, not used)
list_for_each_entry_rcu
list_for_each_continue_rcu (to be deprecated in favor of new
list_for_each_entry_continue_rcu)
Expand Down Expand Up @@ -807,7 +811,8 @@ Quick Quiz #1: Why is this argument naive? How could a deadlock
Answer: Consider the following sequence of events:

1. CPU 0 acquires some unrelated lock, call it
"problematic_lock".
"problematic_lock", disabling irq via
spin_lock_irqsave().

2. CPU 1 enters synchronize_rcu(), write-acquiring
rcu_gp_mutex.
Expand Down Expand Up @@ -894,7 +899,7 @@ Answer: Just as PREEMPT_RT permits preemption of spinlock
ACKNOWLEDGEMENTS

My thanks to the people who helped make this human-readable, including
Jon Walpole, Josh Triplett, Serge Hallyn, and Suzanne Wood.
Jon Walpole, Josh Triplett, Serge Hallyn, Suzanne Wood, and Alan Stern.


For more information, see http://www.rdrop.com/users/paulmck/RCU.
41 changes: 41 additions & 0 deletions Documentation/cputopology.txt
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@@ -0,0 +1,41 @@

Export cpu topology info by sysfs. Items (attributes) are similar
to /proc/cpuinfo.

1) /sys/devices/system/cpu/cpuX/topology/physical_package_id:
represent the physical package id of cpu X;
2) /sys/devices/system/cpu/cpuX/topology/core_id:
represent the cpu core id to cpu X;
3) /sys/devices/system/cpu/cpuX/topology/thread_siblings:
represent the thread siblings to cpu X in the same core;
4) /sys/devices/system/cpu/cpuX/topology/core_siblings:
represent the thread siblings to cpu X in the same physical package;

To implement it in an architecture-neutral way, a new source file,
driver/base/topology.c, is to export the 5 attributes.

If one architecture wants to support this feature, it just needs to
implement 4 defines, typically in file include/asm-XXX/topology.h.
The 4 defines are:
#define topology_physical_package_id(cpu)
#define topology_core_id(cpu)
#define topology_thread_siblings(cpu)
#define topology_core_siblings(cpu)

The type of **_id is int.
The type of siblings is cpumask_t.

To be consistent on all architectures, the 4 attributes should have
deafult values if their values are unavailable. Below is the rule.
1) physical_package_id: If cpu has no physical package id, -1 is the
default value.
2) core_id: If cpu doesn't support multi-core, its core id is 0.
3) thread_siblings: Just include itself, if the cpu doesn't support
HT/multi-thread.
4) core_siblings: Just include itself, if the cpu doesn't support
multi-core and HT/Multi-thread.

So be careful when declaring the 4 defines in include/asm-XXX/topology.h.

If an attribute isn't defined on an architecture, it won't be exported.

57 changes: 25 additions & 32 deletions Documentation/driver-model/overview.txt
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@@ -1,50 +1,43 @@
The Linux Kernel Device Model

Patrick Mochel <mochel@osdl.org>
Patrick Mochel <mochel@digitalimplant.org>

26 August 2002
Drafted 26 August 2002
Updated 31 January 2006


Overview
~~~~~~~~

This driver model is a unification of all the current, disparate driver models
that are currently in the kernel. It is intended to augment the
The Linux Kernel Driver Model is a unification of all the disparate driver
models that were previously used in the kernel. It is intended to augment the
bus-specific drivers for bridges and devices by consolidating a set of data
and operations into globally accessible data structures.

Current driver models implement some sort of tree-like structure (sometimes
just a list) for the devices they control. But, there is no linkage between
the different bus types.
Traditional driver models implemented some sort of tree-like structure
(sometimes just a list) for the devices they control. There wasn't any
uniformity across the different bus types.

A common data structure can provide this linkage with little overhead: when a
bus driver discovers a particular device, it can insert it into the global
tree as well as its local tree. In fact, the local tree becomes just a subset
of the global tree.

Common data fields can also be moved out of the local bus models into the
global model. Some of the manipulations of these fields can also be
consolidated. Most likely, manipulation functions will become a set
of helper functions, which the bus drivers wrap around to include any
bus-specific items.

The common device and bridge interface currently reflects the goals of the
modern PC: namely the ability to do seamless Plug and Play, power management,
and hot plug. (The model dictated by Intel and Microsoft (read: ACPI) ensures
us that any device in the system may fit any of these criteria.)

In reality, not every bus will be able to support such operations. But, most
buses will support a majority of those operations, and all future buses will.
In other words, a bus that doesn't support an operation is the exception,
instead of the other way around.
The current driver model provides a comon, uniform data model for describing
a bus and the devices that can appear under the bus. The unified bus
model includes a set of common attributes which all busses carry, and a set
of common callbacks, such as device discovery during bus probing, bus
shutdown, bus power management, etc.

The common device and bridge interface reflects the goals of the modern
computer: namely the ability to do seamless device "plug and play", power
management, and hot plug. In particular, the model dictated by Intel and
Microsoft (namely ACPI) ensures that almost every device on almost any bus
on an x86-compatible system can work within this paradigm. Of course,
not every bus is able to support all such operations, although most
buses support a most of those operations.


Downstream Access
~~~~~~~~~~~~~~~~~

Common data fields have been moved out of individual bus layers into a common
data structure. But, these fields must still be accessed by the bus layers,
data structure. These fields must still be accessed by the bus layers,
and sometimes by the device-specific drivers.

Other bus layers are encouraged to do what has been done for the PCI layer.
Expand All @@ -53,7 +46,7 @@ struct pci_dev now looks like this:
struct pci_dev {
...

struct device device;
struct device dev;
};

Note first that it is statically allocated. This means only one allocation on
Expand All @@ -64,9 +57,9 @@ the two.

The PCI bus layer freely accesses the fields of struct device. It knows about
the structure of struct pci_dev, and it should know the structure of struct
device. PCI devices that have been converted generally do not touch the fields
of struct device. More precisely, device-specific drivers should not touch
fields of struct device unless there is a strong compelling reason to do so.
device. Individual PCI device drivers that have been converted the the current
driver model generally do not and should not touch the fields of struct device,
unless there is a strong compelling reason to do so.

This abstraction is prevention of unnecessary pain during transitional phases.
If the name of the field changes or is removed, then every downstream driver
Expand Down
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