linux-toradex.git/kernel/trace/ring_buffer.c, branch v2.6.32.52

ring-buffer: Fix typo of time extends per page

2010-10-29T04:44:00+00:00

commit d01343244abdedd18303d0323b518ed9cdcb1988 upstream.

Time stamps for the ring buffer are created by the difference between
two events. Each page of the ring buffer holds a full 64 bit timestamp.
Each event has a 27 bit delta stamp from the last event. The unit of time
is nanoseconds, so 27 bits can hold ~134 milliseconds. If two events
happen more than 134 milliseconds apart, a time extend is inserted
to add more bits for the delta. The time extend has 59 bits, which
is good for ~18 years.

Currently the time extend is committed separately from the event.
If an event is discarded before it is committed, due to filtering,
the time extend still exists. If all events are being filtered, then
after ~134 milliseconds a new time extend will be added to the buffer.

This can only happen till the end of the page. Since each page holds
a full timestamp, there is no reason to add a time extend to the
beginning of a page. Time extends can only fill a page that has actual
data at the beginning, so there is no fear that time extends will fill
more than a page without any data.

When reading an event, a loop is made to skip over time extends
since they are only used to maintain the time stamp and are never
given to the caller. As a paranoid check to prevent the loop running
forever, with the knowledge that time extends may only fill a page,
a check is made that tests the iteration of the loop, and if the
iteration is more than the number of time extends that can fit in a page
a warning is printed and the ring buffer is disabled (all of ftrace
is also disabled with it).

There is another event type that is called a TIMESTAMP which can
hold 64 bits of data in the theoretical case that two events happen
18 years apart. This code has not been implemented, but the name
of this event exists, as well as the structure for it. The
size of a TIMESTAMP is 16 bytes, where as a time extend is only
8 bytes. The macro used to calculate how many time extends can fit on
a page used the TIMESTAMP size instead of the time extend size
cutting the amount in half.

The following test case can easily trigger the warning since we only
need to have half the page filled with time extends to trigger the
warning:

 # cd /sys/kernel/debug/tracing/
 # echo function > current_tracer
 # echo 'common_pid < 0' > events/ftrace/function/filter
 # echo > trace
 # echo 1 > trace_marker
 # sleep 120
 # cat trace

Enabling the function tracer and then setting the filter to only trace
functions where the process id is negative (no events), then clearing
the trace buffer to ensure that we have nothing in the buffer,
then write to trace_marker to add an event to the beginning of a page,
sleep for 2 minutes (only 35 seconds is probably needed, but this
guarantees the bug), and then finally reading the trace which will
trigger the bug.

This patch fixes the typo and prevents the false positive of that warning.

Reported-by: Hans J. Koch 
Tested-by: Hans J. Koch 
Cc: Thomas Gleixner 
Signed-off-by: Steven Rostedt 
Signed-off-by: Greg Kroah-Hartman

ring-buffer: Move disabled check into preempt disable section

2010-04-01T22:58:08+00:00

commit 52fbe9cde7fdb5c6fac196d7ebd2d92d05ef3cd4 upstream.

The ring buffer resizing and resetting relies on a schedule RCU
action. The buffers are disabled, a synchronize_sched() is called
and then the resize or reset takes place.

But this only works if the disabling of the buffers are within the
preempt disabled section, otherwise a window exists that the buffers
can be written to while a reset or resize takes place.

Reported-by: Li Zefan 
Signed-off-by: Lai Jiangshan 
LKML-Reference: <4B949E43.2010906@cn.fujitsu.com>
Signed-off-by: Steven Rostedt 
Signed-off-by: Greg Kroah-Hartman

ring-buffer: Synchronize resizing buffer with reader lock

2009-11-04T05:04:20+00:00

We got a sudden panic when we reduced the size of the
ringbuffer.

We can reproduce the panic by the following steps:

echo 1 > events/sched/enable
cat trace_pipe > /dev/null &

while ((1))
do
echo 12000 > buffer_size_kb
echo 512 > buffer_size_kb
done

(not more than 5 seconds, panic ...)

Reported-by: KOSAKI Motohiro 
Signed-off-by: Lai Jiangshan 
LKML-Reference: <4AF01735.9060409@cn.fujitsu.com>
Signed-off-by: Steven Rostedt

tracing: Remove cpu arg from the rb_time_stamp() function

2009-10-24T09:07:51+00:00

The cpu argument is not used inside the rb_time_stamp() function.
Plus fix a typo.

Signed-off-by: Jiri Olsa 
Signed-off-by: Steven Rostedt 
Cc: Frederic Weisbecker 
LKML-Reference: <20091023233647.118547500@goodmis.org>
Signed-off-by: Ingo Molnar

tracing: Fix comment typo and documentation example

2009-10-24T09:07:50+00:00

Trivial patch to fix a documentation example and to fix a
comment.

Signed-off-by: Jiri Olsa 
Signed-off-by: Steven Rostedt 
Cc: Frederic Weisbecker 
LKML-Reference: <20091023233646.871719877@goodmis.org>
Signed-off-by: Ingo Molnar

includecheck fix: kernel/trace, ring_buffer.c

2009-09-20T11:28:56+00:00

fix the following 'make includecheck' warning:

  kernel/trace/ring_buffer.c: trace.h is included more than once.

Signed-off-by: Jaswinder Singh Rajput 
Cc: Steven Rostedt 
Cc: Ingo Molnar 
Cc: Sam Ravnborg 
LKML-Reference: <1247068617.4382.107.camel@ht.satnam>

ring-buffer: typecast cmpxchg to fix PowerPC warning

2009-09-14T13:41:57+00:00

The cmpxchg used by PowerPC does the following:

  ({									 \
     __typeof__(*(ptr)) _o_ = (o);					 \
     __typeof__(*(ptr)) _n_ = (n);					 \
     (__typeof__(*(ptr))) __cmpxchg((ptr), (unsigned long)_o_,		 \
				    (unsigned long)_n_, sizeof(*(ptr))); \
  })

This does a type check of *ptr to both o and n.

Unfortunately, the code in ring-buffer.c assigns longs to pointers
and pointers to longs and causes a warning on PowerPC:

ring_buffer.c: In function 'rb_head_page_set':
ring_buffer.c:704: warning: initialization makes pointer from integer without a cast
ring_buffer.c:704: warning: initialization makes pointer from integer without a cast
ring_buffer.c: In function 'rb_head_page_replace':
ring_buffer.c:797: warning: initialization makes integer from pointer without a cast

This patch adds the typecasts inside cmpxchg to annotate that a long is
being cast to a pointer and a pointer is being casted to a long and this
removes the PowerPC warnings.

Reported-by: Stephen Rothwell 
Signed-off-by: Steven Rostedt

ring-buffer: consolidate interface of rb_buffer_peek()

2009-09-10T03:54:02+00:00

rb_buffer_peek() operates with struct ring_buffer_per_cpu *cpu_buffer
only. Thus, instead of passing variables buffer and cpu it is better
to use cpu_buffer directly. This also reduces the risk of races since
cpu_buffer is not calculated twice.

Signed-off-by: Robert Richter 
LKML-Reference: <1249045084-3028-1-git-send-email-robert.richter@amd.com>
Signed-off-by: Steven Rostedt

ring-buffer: only enable ring_buffer_swap_cpu when needed

2009-09-04T23:42:22+00:00

Since the ability to swap the cpu buffers adds a small overhead to
the recording of a trace, we only want to add it when needed.

Only the irqsoff and preemptoff tracers use this feature, and both are
not recommended for production kernels. This patch disables its use
when neither irqsoff nor preemptoff is configured.

Signed-off-by: Steven Rostedt

ring-buffer: check for swapped buffers in start of committing

2009-09-04T23:38:42+00:00

Because the irqsoff tracer can swap an internal CPU buffer, it is possible
that a swap happens between the start of the write and before the committing
bit is set (the committing bit will disable swapping).

This patch adds a check for this and will fail the write if it detects it.

Signed-off-by: Steven Rostedt