When adding the EXPORT_SYMBOL to some of the tracing API, I accidently
used EXPORT_SYMBOL instead of EXPORT_SYMBOL_GPL. This patch fixes
that mistake.

[ Impact: export the tracing code only for GPL modules ]
Reported-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

The only references in the kernel to the .text.sched section are in
recordmcount.pl.  Since the code it has is intended to be example code
it should refer to real kernel sections.  So change it to .sched.text
instead.

[ Impact: consistency in comments ]
Signed-off-by: NTim Abbott <tabbott@mit.edu>
LKML-Reference: <1241136371-10768-1-git-send-email-tabbott@mit.edu>
Acked-by: NSam Ravnborg <sam@ravnborg.org>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

As a precaution, it is best to disable writing to the ring buffers
when reseting them.

[ Impact: prevent weird things if write happens during reset ]
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

In the swap page ring buffer code that is used by the ftrace splice code,
we scan the page to increment the counter of entries read.

With the number of entries already in the page we simply need to add it.

[ Impact: speed up reading page from ring buffer ]
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

Currently, when the ring buffer writer overflows the buffer and must
write over non consumed data, we increment the overrun counter by
reading the entries on the page we are about to overwrite. This reads
the entries one by one.

This is not very effecient. This patch adds another entry counter
into each buffer page descriptor that keeps track of the number of
entries on the page. Now on overwrite, the overrun counter simply
needs to add the number of entries that is on the page it is about
to overwrite.

[ Impact: speed up of ring buffer in overwrite mode ]
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

The entries counter in cpu buffer is not atomic. It can be updated by
other interrupts or from another CPU (readers).

But making entries into "atomic_t" causes an atomic operation that can
hurt performance. Instead we convert it to a local_t that will increment
a counter with a local CPU atomic operation (if the arch supports it).

Instead of fighting with readers and overwrites that decrement the counter,
I added a "read" counter. Every time a reader reads an entry it is
incremented.

We already have a overrun counter and with that, the entries counter and
the read counter, we can calculate the total number of entries in the
buffer with:

  (entries - overrun) - read

As long as the total number of entries in the ring buffer is less than
the word size, this will work. But since the entries counter was previously
a long, this is no different than what we had before.

Thanks to Andrew Morton for pointing out in the first version that
atomic_t does not replace unsigned long. I switched to atomic_long_t
even though it is signed. A negative count is most likely a bug.

[ Impact: keep accurate count of cpu buffer entries ]
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

This patch adds stats to the ftrace ring buffers:

 # cat /debugfs/tracing/per_cpu/cpu0/stats
 entries: 42360
 overrun: 30509326
 commit overrun: 0
 nmi dropped: 0

Where entries are the total number of data entries in the buffer.

overrun is the number of entries not consumed and were overwritten by
the writer.

commit overrun is the number of entries dropped due to nested writers
wrapping the buffer before the initial writer finished the commit.

nmi dropped is the number of entries dropped due to the ring buffer
lock being held when an nmi was going to write to the ring buffer.
Note, this field will be meaningless and will go away when the ring
buffer becomes lockless.

[ Impact: let userspace know what is happening in the ring buffers ]
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

The WARN_ON in the ring buffer when a commit is preempted and the
buffer is filled by preceding writes can happen in normal operations.
The WARN_ON makes it look like a bug, not to mention, because
it does not stop tracing and calls printk which can also recurse, this
is prone to deadlock (the WARN_ON is not in a position to recurse).

This patch removes the WARN_ON and replaces it with a counter that
can be retrieved by a tracer. This counter is called commit_overrun.

While at it, I added a nmi_dropped counter to count any time an NMI entry
is dropped because the NMI could not take the spinlock.

[ Impact: prevent deadlock by printing normal case warning ]
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

I'm adding a module to do a series of tests on the ring buffer as well
as benchmarks. This module needs to have more of the ring buffer API
exported. There's nothing wrong with reading the ring buffer from a
module.

[ Impact: allow modules to read pages from the ring buffer ]
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

Document irqs for the newly created docbook.

[ Impact: add documentation ]
Signed-off-by: NJason Baron <jbaron@redhat.com>
Acked-by: NRandy Dunlap <randy.dunlap@oracle.com>
Cc: akpm@linux-foundation.org
Cc: rostedt@goodmis.org
Cc: fweisbec@gmail.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: wcohen@redhat.com
LKML-Reference: <73ff42be3420157667ec548e9b0e409c3cfad05f.1241107197.git.jbaron@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Add tracepoint docbook. This will help us document and understand
what tracepoints are in the kernel. Since there are multiple
macros, and files that contain tracepoints.

[ Impact: add documentation ]
Signed-off-by: NJason Baron <jbaron@redhat.com>
Acked-by: NRandy Dunlap <randy.dunlap@oracle.com>
Cc: akpm@linux-foundation.org
Cc: rostedt@goodmis.org
Cc: fweisbec@gmail.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: wcohen@redhat.com
LKML-Reference: <84160b6bd94aff02455da7e12bad054d34c579a0.1241107197.git.jbaron@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Add support to kernel-doc for tracepoint comments above TRACE_EVENT()
macro definitions. Paves the way for tracepoint docbook.

[ Impact: extend DocBook infrastructure ]
Signed-off-by: NJason Baron <jbaron@redhat.com>
Acked-by: NRandy Dunlap <randy.dunlap@oracle.com>
Cc: akpm@linux-foundation.org
Cc: rostedt@goodmis.org
Cc: fweisbec@gmail.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: wcohen@redhat.com
LKML-Reference: <d80706b6797e277924d2f3ec9af176c6b2951f88.1241107197.git.jbaron@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

"tracing: create automated trace defines" causes this compile error on s390,
as reported by Sachin Sant against linux-next:

 kernel/built-in.o: In function `__do_softirq':
 (.text+0x1c680): undefined reference to `__tracepoint_softirq_entry'

This happens because the definitions of the softirq tracepoints were moved
from kernel/softirq.c to kernel/irq/handle.c. Since s390 doesn't support
generic hardirqs handle.c doesn't get compiled and the definitions are
missing.

So move the tracepoints to softirq.c again.

[ Impact: fix build failure on s390 ]
Reported-by: NSachin Sant <sachinp@in.ibm.com>
Signed-off-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: fweisbec@gmail.com
LKML-Reference: <20090429135139.5fac79b8@osiris.boeblingen.de.ibm.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Replace the current event parser hack with a better one.  Filters are
no longer specified predicate by predicate, but all at once and can
use parens and any of the following operators:

numeric fields:

==, !=, <, <=, >, >=

string fields:

==, !=

predicates can be combined with the logical operators:

&&, ||

examples:

"common_preempt_count > 4" > filter

"((sig >= 10 && sig < 15) || sig == 17) && comm != bash" > filter

If there was an error, the erroneous string along with an error
message can be seen by looking at the filter e.g.:

((sig >= 10 && sig < 15) || dsig == 17) && comm != bash
^
parse_error: Field not found

Currently the caret for an error always appears at the beginning of
the filter; a real position should be used, but the error message
should be useful even without it.

To clear a filter, '0' can be written to the filter file.

Filters can also be set or cleared for a complete subsystem by writing
the same filter as would be written to an individual event to the
filter file at the root of the subsytem.  Note however, that if any
event in the subsystem lacks a field specified in the filter being
set, the set will fail and all filters in the subsytem are
automatically cleared.  This change from the previous version was made
because using only the fields that happen to exist for a given event
would most likely result in a meaningless filter.

Because the logical operators are now implemented as predicates, the
maximum number of predicates in a filter was increased from 8 to 16.

[ Impact: add new, extended trace-filter implementation ]
Signed-off-by: NTom Zanussi <tzanussi@gmail.com>
Acked-by: NSteven Rostedt <rostedt@goodmis.org>
Cc: fweisbec@gmail.com
Cc: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <1240905899.6416.121.camel@tropicana>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

The new filter comparison ops need to be able to distinguish between
signed and unsigned field types, so add an is_signed flag/param to the
event field struct/trace_define_fields().  Also define a simple macro,
is_signed_type() to determine the signedness at compile time, used in the
trace macros.  If the is_signed_type() macro won't work with a specific
type, a new slightly modified version of TRACE_FIELD() called
TRACE_FIELD_SIGN(), allows the signedness to be set explicitly.

[ Impact: extend trace-filter code for new feature ]
Signed-off-by: NTom Zanussi <tzanussi@gmail.com>
Acked-by: NSteven Rostedt <rostedt@goodmis.org>
Cc: fweisbec@gmail.com
Cc: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <1240905893.6416.120.camel@tropicana>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Create a new event_filter object, and move the pred-related members
out of the call and subsystem objects and into the filter object - the
details of the filter implementation don't need to be exposed in the
call and subsystem in any case, and it will also help make the new
parser implementation a little cleaner.

[ Impact: refactor trace-filter code to prepare for new features ]
Signed-off-by: NTom Zanussi <tzanussi@gmail.com>
Acked-by: NSteven Rostedt <rostedt@goodmis.org>
Cc: fweisbec@gmail.com
Cc: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <1240905887.6416.119.camel@tropicana>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Follow up to afcfe024 in Linus' tree
("x86: mmiotrace: quieten spurious warning message")
Signed-off-by: NStuart Bennett <stuart@freedesktop.org>
Acked-by: NPekka Paalanen <pq@iki.fi>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <1240946271-7083-5-git-send-email-stuart@freedesktop.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

* change function names to clear_* from set_*: in reality we only clear
  and restore page presence, and never unconditionally set present.
  Using clear_*({true, false}, ...) is therefore more honest than
  set_*({false, true}, ...)

* upgrade presence storage to pteval_t: doing user-space tracing will
  require saving and manipulation of the _PAGE_PROTNONE bit, in addition
  to the existing _PAGE_PRESENT changes, and having multiple bools stored
  and passed around does not seem optimal

[ Impact: refactor, clean up mmiotrace code ]
Signed-off-by: NStuart Bennett <stuart@freedesktop.org>
Acked-by: NPekka Paalanen <pq@iki.fi>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <1240946271-7083-4-git-send-email-stuart@freedesktop.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

kmmio_probe being *p and kmmio_fault_page being sometimes *f and
sometimes *p is not helpful.

[ Impact: cleanup ]
Signed-off-by: NStuart Bennett <stuart@freedesktop.org>
Acked-by: NPekka Paalanen <pq@iki.fi>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <1240946271-7083-3-git-send-email-stuart@freedesktop.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

The warning output in trace_recursive_lock uses %d for a long when
it should be %ld.

[ Impact: fix compile warning ]
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

Splice works with pages, it is much more effecient to use an entire
page than to copy bits over several pages.

Using logdev to trace the internals of the splice mechanism, I was
able to see that splice can be very aggressive. When tracing is
occurring, and the reader caught up to the writer, and the writer
is on the reader page, the reader will copy what is there into the
splice page. Splice may iterate over several pages and if the
writer is still writing to the page, the reader will keep copying
bits to new pages to pass to userspace.

This patch changes it to only pass data to userspace if the page
is full (the writer has left the page). This has a small side effect
that splice can not read a partial page, and must wait for the
page to fill. This should not be an issue. If tracing has stopped,
then a use of "read" will still read all of the page.

[ Impact: better performance for ring buffer splice code ]
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

The splice code allocates a page even when the ring buffer is empty.
It detects the ring buffer being empty when it it fails to copy
anything from the ring buffer into the page.

This patch adds a check to see if there is anything in the ring buffer
before allocating a page.

Thanks to logdev for letting me trace the tracer to find this.

[ Impact: speed up due to removing unnecessary allocation ]
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

The pages allocated for the splice binary buffer did not initialize
the ref count correctly. This caused pages not to be freed and causes
a drastic memory leak.

Thanks to logdev I was able to trace the tracer to find where the leak
was.

[ Impact: stop memory leak when using splice ]
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

ftrace_dump is used for printing out the contents of the ftrace ring buffer
to the console on failure. Currently it uses a spinlock to synchronize
the output from multiple failures on different CPUs. This spin lock
currently is a normal spinlock and can cause issues with lockdep and
lock tracing.

This patch converts it to raw since it is for error handling only.
The lock is local to the ftrace_dump and is not used by any other
infrastructure.

[ Impact: prevent ftrace_dump from locking up by internal tracing ]
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

For proper module reference counting, the file_operations that modules use
must have the "owner" field set to the module. Unfortunately, the trace events
use share file_operations. The same file_operations are used by all both
kernel core and all modules.

This patch makes the modules allocate their own file_operations and
copies the functions from the core kernel. This allows those file
operations to be owned by the module.

Care is taken to free this code on module unload.

Thanks to Greg KH for reminding me that file_operations must be owned
by the module to have reference counting take place.

[ Impact: fix modular tracepoints / potential crash ]
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>
Acked-by: NGreg Kroah-Hartman <gregkh@suse.de>

With modules being able to add trace events, and the max trace event
counter is 16 bits (65536) we can overflow the counter easily
with a simple while loop adding and removing modules that contain
trace events.

This patch links together the registered trace events and on overflow
searches for available trace event ids. It will still fail if
over 65536 events are registered, but considering that a typical
kernel only has 22000 functions, 65000 events should be sufficient.
Reported-by: NLi Zefan <lizf@cn.fujitsu.com>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

The TRACE_FORMAT macro has been deprecated by the TRACE_EVENT macro.
There are no more users. All new users must use the TRACE_EVENT macro.

[ Impact: remove old functionality ]

Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

The TRACE_FORMAT will soon be deprecated. This patch converts it to
the TRACE_EVENT macro.

Note, this change should also speed up the tracing.

[ Impact: remove a user of deprecated TRACE_FORMAT ]

Cc: Jason Baron <jbaron@redhat.com>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

The TRACE_FORMAT will soon be deprecated. This patch converts it to
the TRACE_EVENT macro.

Note, this change should also speed up the tracing.

[ Impact: remove a user of deprecated TRACE_FORMAT ]

Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

RB_MAX_SMALL_DATA = 28bytes is too small for most tracers, it wastes
an 'u32' to save the actually length for events which data size > 28.

This fix uses compressed event header and enlarges RB_MAX_SMALL_DATA.

[ Impact: saves about 0%-12.5%(depends on tracer) memory in ring_buffer ]
Signed-off-by: NLai Jiangshan <laijs@cn.fujitsu.com>
LKML-Reference: <49F13189.3090000@cn.fujitsu.com>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

In case a module uses the TRACE_EVENT macro for creating automated
events in ftrace, it may choose to use a different file name
than the defined system name, or choose to use a different path than
the default "include/trace/events" include path.

If this is done, then before including trace/define_trace.h the
header would define either "TRACE_INCLUDE_FILE" for the file
name or "TRACE_INCLUDE_PATH" for the include path.

If it does not define these, then the define_trace.h defines them
instead. If define trace defines them, then define_trace.h should
also undefine them before exiting. To do this a macro is used
to note this:

 #ifndef TRACE_INCLUDE_FILE
 # define TRACE_INCLUDE_FILE TRACE_SYSTEM
 # define UNDEF_TRACE_INCLUDE_FILE
 #endif

[...]

 #ifdef UNDEF_TRACE_INCLUDE_FILE
 # undef TRACE_INCLUDE_FILE
 # undef UNDEF_TRACE_INCLUDE_FILE
 #endif

The UNDEF_TRACE_INCLUDE_FILE acts as a CPP variable to know to undef
the TRACE_INCLUDE_FILE before leaving define_trace.h.

Unfortunately, due to cut and paste errors, the macros between
FILE and PATH got mixed up.

[ Impact: undef TRACE_INCLUDE_FILE and/or TRACE_INCLUDE_PATH when needed ]
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

currently these are paravirtulaized, doesn't appear any callers rely on
this (no pv_ops backends are using native_tlb and overriding cr3/4
access).

[ Impact: fix lockdep warning with paravirt and function tracer ]
Signed-off-by: NChris Wright <chrisw@sous-sol.org>
LKML-Reference: <20090423172138.GR3036@sequoia.sous-sol.org>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

The events exported by TRACE_EVENT are automated and are guaranteed
to be correct when used.

The internal ftrace structures on the other hand are more manually
exported. These require the ftrace maintainer to make sure they
are up to date.

This patch adds a size check to help flag when a type changes in
an internal ftrace data structure, and the update needs to be reflected
in the export.

If a export is incorrect, then the only harm is that the user space
tools will not know how to correctly read the internal structures of
ftrace.

[ Impact: help prevent inconsistent ftrace format print outs ]
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

With the new event tracing registration, we must increase the number
of events that can be registered. Currently the type field is only
one byte, which leaves us only 256 possible events.

Since we do not save the CPU number in the tracer anymore (it is determined
by the per cpu ring buffer that is used) we have an extra byte to use.

This patch increases the size of type from 1 byte (256 events) to
2 bytes (65,536 events).

It also adds a WARN_ON_ONCE if we exceed that limit.

[ Impact: allow more than 255 events ]
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

The code had the following outside the lock:

        if (next != wakeup_task)
                return;

        pc = preempt_count();

        /* The task we are waiting for is waking up */
        data = wakeup_trace->data[wakeup_cpu];

On initialization, wakeup_task is NULL and wakeup_cpu -1. This code
is not under a lock. If wakeup_task is set on another CPU as that
task is waking up, we can see the wakeup_task before wakeup_cpu is
set. If we read wakeup_cpu while it is still -1 then we will have
a bad data pointer.

This patch moves the reading of wakeup_cpu within the protection of
the spinlock used to protect the writing of wakeup_cpu and wakeup_task.

[ Impact: remove possible race causing invalid pointer dereference ]
Reported-by: NManeesh Soni <maneesh@in.ibm.com>
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>

The __get_str() macro is used in a code part then its content should be
protected with parenthesis.

[ Impact: make macro definition more robust ]
Reported-by: NSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>

Now that we can support the dynamic sized string, make the lock tracing
able to use it, making it safe against modules removal and consuming
the right amount of memory needed for each lock name

Changes in v2:
adapt to the __ending_string() updates and the opening_string() removal.

[ Impact: protect lock tracer against module removal ]
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Steven Rostedt <rostedt@goodmis.org>

This patch provides the support for dynamic size strings on
event tracing.

The key concept is to use a structure with an ending char array field of
undefined size and use such ability to allocate the minimal size on the
ring buffer to make one or more string entries fit inside, as opposite
to a fixed length strings with upper bound.

The strings themselves are represented using fields which have an offset
value from the beginning of the entry.

This patch provides three new macros:

__string(item, src)

This one declares a string to the structure inside TP_STRUCT__entry.
You need to provide the name of the string field and the source that will
be copied inside.
This will also add the dynamic size of the string needed for the ring
buffer entry allocation.
A stack allocated structure is used to temporarily store the offset
of each strings, avoiding double calls to strlen() on each event
insertion.

__get_str(field)

This one will give you a pointer to the string you have created. This
is an abstract helper to resolve the absolute address given the field
name which is a relative address from the beginning of the trace_structure.

__assign_str(dst, src)

Use this macro to automatically perform the string copy from src to
dst. src must be a variable to assign and dst is the name of a __string
field.

Example on how to use it:

TRACE_EVENT(my_event,
	TP_PROTO(char *src1, char *src2),

	TP_ARGS(src1, src2),
	TP_STRUCT__entry(
		__string(str1, src1)
		__string(str2, src2)
	),
	TP_fast_assign(
		__assign_str(str1, src1);
		__assign_str(str2, src2);
	),
	TP_printk("%s %s", __get_str(src1), __get_str(src2))
)

Of course you can mix-up any __field or __array inside this
TRACE_EVENT. The position of the __string or __assign_str
doesn't matter.

Changes in v2:

Address the suggestion of Steven Rostedt: drop the opening_string() macro
and redefine __ending_string() to get the size of the string to be copied
instead of overwritting the whole ring buffer allocation.

Changes in v3:

Address other suggestions of Steven Rostedt and Peter Zijlstra with
some changes: drop the __ending_string and the need to have only one
string field.
Use offsets instead of absolute addresses.

[ Impact: allow more compact memory usage for string tracing ]
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>

struct trace_entry->type is unsigned char, while trace event's id is
int type, thus for a event with id >= 256, it's entry->type is cast
to (id % 256), and then we can't see the trace output of this event.

 # insmod trace-events-sample.ko
 # echo foo_bar > /mnt/tracing/set_event
 # cat /debug/tracing/events/trace-events-sample/foo_bar/id
 256
 # cat /mnt/tracing/trace_pipe
           <...>-3548  [001]   215.091142: Unknown type 0
           <...>-3548  [001]   216.089207: Unknown type 0
           <...>-3548  [001]   217.087271: Unknown type 0
           <...>-3548  [001]   218.085332: Unknown type 0

[ Impact: fix output for trace events with id >= 256 ]
Signed-off-by: NLi Zefan <lizf@cn.fujitsu.com>
Acked-by: NFrederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Tom Zanussi <tzanussi@gmail.com>
LKML-Reference: <49EEDB0E.5070207@cn.fujitsu.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

On boot up, to save memory, ftrace allocates the minimum buffer
which is two pages. Ftrace also goes through a series of tests
(when configured) on boot up. These tests can fill up a page within
a single interrupt.

The ring buffer also has a WARN_ON when it detects that the buffer was
completely filled within a single commit (other commits are allowed to
be nested).

Combine the small buffer on start up, with the tests that can fill more
than a single page within an interrupt, this can trigger the WARN_ON.

This patch makes the WARN_ON only happen when the ring buffer consists
of more than two pages.

[ Impact: prevent false WARN_ON in ftrace startup tests ]
Reported-by: NIngo Molnar <mingo@elte.hu>
LKML-Reference: <20090421094616.GA14561@elte.hu>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>