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r: 280127
b: refs/heads/master
c: 44ad56b
h: refs/heads/master
i:
  280125: 88d3d97
  280123: 577140d
  280119: a94ba2f
  280111: e452b7f
  280095: 2d576aa
  280063: 1c30545
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David Daney authored and Rob Herring committed Dec 19, 2011
1 parent 7a050b3 commit 6503821
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2 changes: 1 addition & 1 deletion [refs]
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---
refs/heads/master: 2d51daaa615e4724f24e43fa01e705c40551080a
refs/heads/master: 44ad56b7df54cbc8063b46883d183e4e2f09f831
50 changes: 0 additions & 50 deletions trunk/Documentation/DocBook/debugobjects.tmpl
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Expand Up @@ -96,7 +96,6 @@
<listitem><para>debug_object_deactivate</para></listitem>
<listitem><para>debug_object_destroy</para></listitem>
<listitem><para>debug_object_free</para></listitem>
<listitem><para>debug_object_assert_init</para></listitem>
</itemizedlist>
Each of these functions takes the address of the real object and
a pointer to the object type specific debug description
Expand Down Expand Up @@ -274,26 +273,6 @@
debug checks.
</para>
</sect1>

<sect1 id="debug_object_assert_init">
<title>debug_object_assert_init</title>
<para>
This function is called to assert that an object has been
initialized.
</para>
<para>
When the real object is not tracked by debugobjects, it calls
fixup_assert_init of the object type description structure
provided by the caller, with the hardcoded object state
ODEBUG_NOT_AVAILABLE. The fixup function can correct the problem
by calling debug_object_init and other specific initializing
functions.
</para>
<para>
When the real object is already tracked by debugobjects it is
ignored.
</para>
</sect1>
</chapter>
<chapter id="fixupfunctions">
<title>Fixup functions</title>
Expand Down Expand Up @@ -402,35 +381,6 @@
statistics.
</para>
</sect1>
<sect1 id="fixup_assert_init">
<title>fixup_assert_init</title>
<para>
This function is called from the debug code whenever a problem
in debug_object_assert_init is detected.
</para>
<para>
Called from debug_object_assert_init() with a hardcoded state
ODEBUG_STATE_NOTAVAILABLE when the object is not found in the
debug bucket.
</para>
<para>
The function returns 1 when the fixup was successful,
otherwise 0. The return value is used to update the
statistics.
</para>
<para>
Note, this function should make sure debug_object_init() is
called before returning.
</para>
<para>
The handling of statically initialized objects is a special
case. The fixup function should check if this is a legitimate
case of a statically initialized object or not. In this case only
debug_object_init() should be called to make the object known to
the tracker. Then the function should return 0 because this is not
a real fixup.
</para>
</sect1>
</chapter>
<chapter id="bugs">
<title>Known Bugs And Assumptions</title>
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4 changes: 2 additions & 2 deletions trunk/Documentation/HOWTO
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Expand Up @@ -275,8 +275,8 @@ versions.
If no 2.6.x.y kernel is available, then the highest numbered 2.6.x
kernel is the current stable kernel.

2.6.x.y are maintained by the "stable" team <stable@vger.kernel.org>, and
are released as needs dictate. The normal release period is approximately
2.6.x.y are maintained by the "stable" team <stable@kernel.org>, and are
released as needs dictate. The normal release period is approximately
two weeks, but it can be longer if there are no pressing problems. A
security-related problem, instead, can cause a release to happen almost
instantly.
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6 changes: 0 additions & 6 deletions trunk/Documentation/RCU/checklist.txt
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Expand Up @@ -328,12 +328,6 @@ over a rather long period of time, but improvements are always welcome!
RCU rather than SRCU, because RCU is almost always faster and
easier to use than is SRCU.

If you need to enter your read-side critical section in a
hardirq or exception handler, and then exit that same read-side
critical section in the task that was interrupted, then you need
to srcu_read_lock_raw() and srcu_read_unlock_raw(), which avoid
the lockdep checking that would otherwise this practice illegal.

Also unlike other forms of RCU, explicit initialization
and cleanup is required via init_srcu_struct() and
cleanup_srcu_struct(). These are passed a "struct srcu_struct"
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10 changes: 5 additions & 5 deletions trunk/Documentation/RCU/rcu.txt
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Expand Up @@ -38,11 +38,11 @@ o How can the updater tell when a grace period has completed

Preemptible variants of RCU (CONFIG_TREE_PREEMPT_RCU) get the
same effect, but require that the readers manipulate CPU-local
counters. These counters allow limited types of blocking within
RCU read-side critical sections. SRCU also uses CPU-local
counters, and permits general blocking within RCU read-side
critical sections. These variants of RCU detect grace periods
by sampling these counters.
counters. These counters allow limited types of blocking
within RCU read-side critical sections. SRCU also uses
CPU-local counters, and permits general blocking within
RCU read-side critical sections. These two variants of
RCU detect grace periods by sampling these counters.

o If I am running on a uniprocessor kernel, which can only do one
thing at a time, why should I wait for a grace period?
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16 changes: 6 additions & 10 deletions trunk/Documentation/RCU/stallwarn.txt
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Expand Up @@ -101,11 +101,6 @@ o A CPU-bound real-time task in a CONFIG_PREEMPT_RT kernel that
CONFIG_TREE_PREEMPT_RCU case, you might see stall-warning
messages.

o A hardware or software issue shuts off the scheduler-clock
interrupt on a CPU that is not in dyntick-idle mode. This
problem really has happened, and seems to be most likely to
result in RCU CPU stall warnings for CONFIG_NO_HZ=n kernels.

o A bug in the RCU implementation.

o A hardware failure. This is quite unlikely, but has occurred
Expand All @@ -114,11 +109,12 @@ o A hardware failure. This is quite unlikely, but has occurred
This resulted in a series of RCU CPU stall warnings, eventually
leading the realization that the CPU had failed.

The RCU, RCU-sched, and RCU-bh implementations have CPU stall warning.
SRCU does not have its own CPU stall warnings, but its calls to
synchronize_sched() will result in RCU-sched detecting RCU-sched-related
CPU stalls. Please note that RCU only detects CPU stalls when there is
a grace period in progress. No grace period, no CPU stall warnings.
The RCU, RCU-sched, and RCU-bh implementations have CPU stall
warning. SRCU does not have its own CPU stall warnings, but its
calls to synchronize_sched() will result in RCU-sched detecting
RCU-sched-related CPU stalls. Please note that RCU only detects
CPU stalls when there is a grace period in progress. No grace period,
no CPU stall warnings.

To diagnose the cause of the stall, inspect the stack traces.
The offending function will usually be near the top of the stack.
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13 changes: 0 additions & 13 deletions trunk/Documentation/RCU/torture.txt
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Expand Up @@ -61,24 +61,11 @@ nreaders This is the number of RCU reading threads supported.
To properly exercise RCU implementations with preemptible
read-side critical sections.

onoff_interval
The number of seconds between each attempt to execute a
randomly selected CPU-hotplug operation. Defaults to
zero, which disables CPU hotplugging. In HOTPLUG_CPU=n
kernels, rcutorture will silently refuse to do any
CPU-hotplug operations regardless of what value is
specified for onoff_interval.

shuffle_interval
The number of seconds to keep the test threads affinitied
to a particular subset of the CPUs, defaults to 3 seconds.
Used in conjunction with test_no_idle_hz.

shutdown_secs The number of seconds to run the test before terminating
the test and powering off the system. The default is
zero, which disables test termination and system shutdown.
This capability is useful for automated testing.

stat_interval The number of seconds between output of torture
statistics (via printk()). Regardless of the interval,
statistics are printed when the module is unloaded.
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4 changes: 4 additions & 0 deletions trunk/Documentation/RCU/trace.txt
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Expand Up @@ -105,10 +105,14 @@ o "dt" is the current value of the dyntick counter that is incremented
or one greater than the interrupt-nesting depth otherwise.
The number after the second "/" is the NMI nesting depth.

This field is displayed only for CONFIG_NO_HZ kernels.

o "df" is the number of times that some other CPU has forced a
quiescent state on behalf of this CPU due to this CPU being in
dynticks-idle state.

This field is displayed only for CONFIG_NO_HZ kernels.

o "of" is the number of times that some other CPU has forced a
quiescent state on behalf of this CPU due to this CPU being
offline. In a perfect world, this might never happen, but it
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19 changes: 5 additions & 14 deletions trunk/Documentation/RCU/whatisRCU.txt
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Expand Up @@ -4,7 +4,6 @@ to start learning about RCU:
1. What is RCU, Fundamentally? http://lwn.net/Articles/262464/
2. What is RCU? Part 2: Usage http://lwn.net/Articles/263130/
3. RCU part 3: the RCU API http://lwn.net/Articles/264090/
4. The RCU API, 2010 Edition http://lwn.net/Articles/418853/


What is RCU?
Expand Down Expand Up @@ -835,8 +834,6 @@ SRCU: Critical sections Grace period Barrier

srcu_read_lock synchronize_srcu N/A
srcu_read_unlock synchronize_srcu_expedited
srcu_read_lock_raw
srcu_read_unlock_raw
srcu_dereference

SRCU: Initialization/cleanup
Expand All @@ -858,33 +855,27 @@ list can be helpful:

a. Will readers need to block? If so, you need SRCU.

b. Is it necessary to start a read-side critical section in a
hardirq handler or exception handler, and then to complete
this read-side critical section in the task that was
interrupted? If so, you need SRCU's srcu_read_lock_raw() and
srcu_read_unlock_raw() primitives.

c. What about the -rt patchset? If readers would need to block
b. What about the -rt patchset? If readers would need to block
in an non-rt kernel, you need SRCU. If readers would block
in a -rt kernel, but not in a non-rt kernel, SRCU is not
necessary.

d. Do you need to treat NMI handlers, hardirq handlers,
c. Do you need to treat NMI handlers, hardirq handlers,
and code segments with preemption disabled (whether
via preempt_disable(), local_irq_save(), local_bh_disable(),
or some other mechanism) as if they were explicit RCU readers?
If so, you need RCU-sched.

e. Do you need RCU grace periods to complete even in the face
d. Do you need RCU grace periods to complete even in the face
of softirq monopolization of one or more of the CPUs? For
example, is your code subject to network-based denial-of-service
attacks? If so, you need RCU-bh.

f. Is your workload too update-intensive for normal use of
e. Is your workload too update-intensive for normal use of
RCU, but inappropriate for other synchronization mechanisms?
If so, consider SLAB_DESTROY_BY_RCU. But please be careful!

g. Otherwise, use RCU.
f. Otherwise, use RCU.

Of course, this all assumes that you have determined that RCU is in fact
the right tool for your job.
Expand Down
11 changes: 6 additions & 5 deletions trunk/Documentation/arm/memory.txt
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Expand Up @@ -51,14 +51,15 @@ ffc00000 ffefffff DMA memory mapping region. Memory returned
ff000000 ffbfffff Reserved for future expansion of DMA
mapping region.

VMALLOC_END feffffff Free for platform use, recommended.
VMALLOC_END must be aligned to a 2MB
boundary.

VMALLOC_START VMALLOC_END-1 vmalloc() / ioremap() space.
Memory returned by vmalloc/ioremap will
be dynamically placed in this region.
Machine specific static mappings are also
located here through iotable_init().
VMALLOC_START is based upon the value
of the high_memory variable, and VMALLOC_END
is equal to 0xff000000.
VMALLOC_START may be based upon the value
of the high_memory variable.

PAGE_OFFSET high_memory-1 Kernel direct-mapped RAM region.
This maps the platforms RAM, and typically
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87 changes: 0 additions & 87 deletions trunk/Documentation/atomic_ops.txt
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Expand Up @@ -84,93 +84,6 @@ compiler optimizes the section accessing atomic_t variables.

*** YOU HAVE BEEN WARNED! ***

Properly aligned pointers, longs, ints, and chars (and unsigned
equivalents) may be atomically loaded from and stored to in the same
sense as described for atomic_read() and atomic_set(). The ACCESS_ONCE()
macro should be used to prevent the compiler from using optimizations
that might otherwise optimize accesses out of existence on the one hand,
or that might create unsolicited accesses on the other.

For example consider the following code:

while (a > 0)
do_something();

If the compiler can prove that do_something() does not store to the
variable a, then the compiler is within its rights transforming this to
the following:

tmp = a;
if (a > 0)
for (;;)
do_something();

If you don't want the compiler to do this (and you probably don't), then
you should use something like the following:

while (ACCESS_ONCE(a) < 0)
do_something();

Alternatively, you could place a barrier() call in the loop.

For another example, consider the following code:

tmp_a = a;
do_something_with(tmp_a);
do_something_else_with(tmp_a);

If the compiler can prove that do_something_with() does not store to the
variable a, then the compiler is within its rights to manufacture an
additional load as follows:

tmp_a = a;
do_something_with(tmp_a);
tmp_a = a;
do_something_else_with(tmp_a);

This could fatally confuse your code if it expected the same value
to be passed to do_something_with() and do_something_else_with().

The compiler would be likely to manufacture this additional load if
do_something_with() was an inline function that made very heavy use
of registers: reloading from variable a could save a flush to the
stack and later reload. To prevent the compiler from attacking your
code in this manner, write the following:

tmp_a = ACCESS_ONCE(a);
do_something_with(tmp_a);
do_something_else_with(tmp_a);

For a final example, consider the following code, assuming that the
variable a is set at boot time before the second CPU is brought online
and never changed later, so that memory barriers are not needed:

if (a)
b = 9;
else
b = 42;

The compiler is within its rights to manufacture an additional store
by transforming the above code into the following:

b = 42;
if (a)
b = 9;

This could come as a fatal surprise to other code running concurrently
that expected b to never have the value 42 if a was zero. To prevent
the compiler from doing this, write something like:

if (a)
ACCESS_ONCE(b) = 9;
else
ACCESS_ONCE(b) = 42;

Don't even -think- about doing this without proper use of memory barriers,
locks, or atomic operations if variable a can change at runtime!

*** WARNING: ACCESS_ONCE() DOES NOT IMPLY A BARRIER! ***

Now, we move onto the atomic operation interfaces typically implemented with
the help of assembly code.

Expand Down
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