In the hot path of the ring buffer "__rb_reserve_next" there's a big
if statement that does not even return back to the work flow.

	code;

	if (cross to next page) {

		[ lots of code ]

		return;
	}

	more code;

The condition is even the unlikely path, although we do not denote it
with an unlikely because gcc is fine with it. The condition is true when
the write crosses a page boundary, and we need to start at a new page.

Having this if statement makes it hard to read, but calling another
function to do the work is also not appropriate, because we are using a lot
of variables that were set before the if statement, and we do not want to
send them as parameters.

This patch changes it to a goto:

	code;

	if (cross to next page)
		goto next_page;

	more code;

	return;

next_page:

	[ lots of code]

This makes the code easier to understand, and a bit more obvious.

The output from gcc is practically identical. For some reason, gcc decided
to use different registers when I switched it to a goto. But other than that,
the logic is the same.

[ Impact: easier to read code ]
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

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>

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>

"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>

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>

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>

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>

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>

Suppose we would like to trace all tasks named '123', but this
will fail:

 # echo 'parent_comm == 123' > events/sched/sched_process_fork/filter
 bash: echo: write error: Invalid argument

Don't guess the type of the filter pred in filter_parse(), but instead
we check it in __filter_add_pred().

[ Impact: extend allowed filter field string values ]
Signed-off-by: NLi Zefan <lizf@cn.fujitsu.com>
Cc: Tom Zanussi <tzanussi@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <49ED8DEB.6000700@cn.fujitsu.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

If writing subsys->filter returns EINVAL or ENOSPC, the original
filters in subsys/ and subsys/events/ will be removed. This is
definitely wrong.

[ Impact: fix filter setting semantics on error condition ]
Signed-off-by: NLi Zefan <lizf@cn.fujitsu.com>
Cc: Tom Zanussi <tzanussi@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <49ED8DD2.2070700@cn.fujitsu.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

The startup tests for the event tracer also runs with the function
tracer enabled. The "wakeup" version of the trace commit was used
which can grab spinlocks. If a task was preempted by an NMI
that called a function being traced, it could deadlock due to the
function tracer trying to grab the same lock.

Thanks to Frederic Weisbecker for pointing out where the bug was.
Reported-by: NIngo Molnar <mingo@elte.hu>
Reported-by: NFrederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

Althought using the irq level (hardirq_count, softirq_count and in_nmi)
was nice to detect bad recursion right away, but since the counters are
not atomically updated with respect to the interrupts, the function tracer
might trigger the test from an interrupt handler before the hardirq_count
is updated. This will trigger a false warning.

This patch converts the recursive detection to a simple counter.
If the depth is greater than 16 then the recursive detection will trigger.
16 is more than enough for any nested interrupts.

[ Impact: fix false positive trace recursion detection ]
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

The ring_buffer_event_discard is not tied to ring_buffer_lock_reserve.
It can be called inside or outside the reserve/commit. Even if it
is called inside the reserve/commit the commit part must also be called.

Only ring_buffer_discard_commit can be used as a replacement for
ring_buffer_unlock_commit.

This patch removes the trace_recursive_unlock from ring_buffer_event_discard
since it would be the wrong place to do so.

[Impact: prevent breakage in trace recursive testing ]

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

The recursive tests to detect same level recursion in the ring buffers
did not account for the hard/softirq_counts to be shifted. Thus the
numbers could be larger than then mask to be tested.

This patch includes the shift for the calculation of the irq depth.

[ Impact: stop false positives in trace recursion detection ]
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

The late_initcall calls a helper function instead of the proper
init event selftest function.

This update may have been lost due to conflicting merges.

[ Impact: fix compiler warning and call extended event trace self tests ]
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

Currently we have two configs: EVENT_TRACING and EVENT_TRACER.
All tracers enable EVENT_TRACING. The EVENT_TRACER is only a
convenience to enable the EVENT_TRACING when no other tracers
are enabled.

The names EVENT_TRACER and EVENT_TRACING are too similar and confusing.
This patch renames EVENT_TRACER to ENABLE_EVENT_TRACING to be more
appropriate to what it actually does, as well as add a comment in
the help menu to explain the option's purpose.

[ Impact: rename config option to reduce confusion ]
Reported-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

During testing we often use randconfig to test various kernels.
The current configuration set up does not give an easy way to disable
all tracing with a single config. The case where randconfig would
test all tracing disabled is very unlikely.

This patch adds a config option to enable or disable all tracing.
It is hooked into the tracing menu just like other submenus are done.

[ Impact: allow randconfig to easily produce all traces disabled ]
Reported-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

This patch makes the branch profiling into a choice selection:

  None               - no branch profiling
  likely/unlikely    - only profile likely/unlikely branches
  all                - profile all branches

The all profiler will also enable the likely/unlikely branches.

This does not change the way the profiler works or the dependencies
between the profilers.

What this patch does, is keep the branch profiling from being selected
by an allyesconfig make. The branch profiler is very intrusive and
it is known to break various architecture builds when selected as an
allyesconfig.

[ Impact: prevent branch profiler from being selected in allyesconfig ]
Reported-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Reported-by: NAl Viro <viro@zeniv.linux.org.uk>
Reported-by: NStephen Rothwell <sfr@canb.auug.org.au>
Reported-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

The pair of helpers trace_recursive_lock() and trace_recursive_unlock()
have been introduced recently to provide generic tracing recursion
protection.

They are used in a symetric way:

 - trace_recursive_lock() on buffer reserve
 - trace_recursive_unlock() on buffer commit

However sometimes, we don't commit but discard on entry
to the buffer, ie: in case of filter checking.

Then we must also unlock the recursion protection on discard time,
otherwise the tracing gets definitely deactivated and a warning
is raised spuriously, such as:

111.119821] ------------[ cut here ]------------
[  111.119829] WARNING: at kernel/trace/ring_buffer.c:1498 ring_buffer_lock_reserve+0x1b7/0x1d0()
[  111.119835] Hardware name: AMILO Li 2727
[  111.119839] Modules linked in:
[  111.119846] Pid: 5731, comm: Xorg Tainted: G        W  2.6.30-rc1 #69
[  111.119851] Call Trace:
[  111.119863]  [<ffffffff8025ce68>] warn_slowpath+0xd8/0x130
[  111.119873]  [<ffffffff8028a30f>] ? __lock_acquire+0x19f/0x1ae0
[  111.119882]  [<ffffffff8028a30f>] ? __lock_acquire+0x19f/0x1ae0
[  111.119891]  [<ffffffff802199b0>] ? native_sched_clock+0x20/0x70
[  111.119899]  [<ffffffff80286dee>] ? put_lock_stats+0xe/0x30
[  111.119906]  [<ffffffff80286eb8>] ? lock_release_holdtime+0xa8/0x150
[  111.119913]  [<ffffffff802c8ae7>] ring_buffer_lock_reserve+0x1b7/0x1d0
[  111.119921]  [<ffffffff802cd110>] trace_buffer_lock_reserve+0x30/0x70
[  111.119930]  [<ffffffff802ce000>] trace_current_buffer_lock_reserve+0x20/0x30
[  111.119939]  [<ffffffff802474e8>] ftrace_raw_event_sched_switch+0x58/0x100
[  111.119948]  [<ffffffff808103b7>] __schedule+0x3a7/0x4cd
[  111.119957]  [<ffffffff80211b56>] ? ftrace_call+0x5/0x2b
[  111.119964]  [<ffffffff80211b56>] ? ftrace_call+0x5/0x2b
[  111.119971]  [<ffffffff80810c08>] schedule+0x18/0x40
[  111.119977]  [<ffffffff80810e09>] preempt_schedule+0x39/0x60
[  111.119985]  [<ffffffff80813bd3>] _read_unlock+0x53/0x60
[  111.119993]  [<ffffffff807259d2>] sock_def_readable+0x72/0x80
[  111.120002]  [<ffffffff807ad5ed>] unix_stream_sendmsg+0x24d/0x3d0
[  111.120011]  [<ffffffff807219a3>] sock_aio_write+0x143/0x160
[  111.120019]  [<ffffffff80211b56>] ? ftrace_call+0x5/0x2b
[  111.120026]  [<ffffffff80721860>] ? sock_aio_write+0x0/0x160
[  111.120033]  [<ffffffff80721860>] ? sock_aio_write+0x0/0x160
[  111.120042]  [<ffffffff8031c283>] do_sync_readv_writev+0xf3/0x140
[  111.120049]  [<ffffffff80211b56>] ? ftrace_call+0x5/0x2b
[  111.120057]  [<ffffffff80276ff0>] ? autoremove_wake_function+0x0/0x40
[  111.120067]  [<ffffffff8045d489>] ? cap_file_permission+0x9/0x10
[  111.120074]  [<ffffffff8045c1e6>] ? security_file_permission+0x16/0x20
[  111.120082]  [<ffffffff8031cab4>] do_readv_writev+0xd4/0x1f0
[  111.120089]  [<ffffffff80211b56>] ? ftrace_call+0x5/0x2b
[  111.120097]  [<ffffffff80211b56>] ? ftrace_call+0x5/0x2b
[  111.120105]  [<ffffffff8031cc18>] vfs_writev+0x48/0x70
[  111.120111]  [<ffffffff8031cd65>] sys_writev+0x55/0xc0
[  111.120119]  [<ffffffff80211e32>] system_call_fastpath+0x16/0x1b
[  111.120125] ---[ end trace 15605f4e98d5ccb5 ]---

[ Impact: fix spurious warning triggering tracing shutdown ]
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>

In case of tracing recursion detection, we only get the stacktrace.
But the current context may be very useful to debug the issue.

This patch adds the softirq/hardirq/nmi context with the warning
using lockdep context display to have a familiar output.

v2: Use printk_once()
v3: drop {hardirq,softirq}_context which depend on lockdep,
    only keep what is part of current->trace_recursion,
    sufficient to debug the warning source.

[ Impact: print context necessary to debug recursion ]
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>

trace_printk can be called from any context, including NMIs.
If this happens, then we must test for for recursion before
grabbing any spinlocks.

This patch prevents trace_printk from being called recursively.

[ Impact: prevent hard lockup in lockdep event tracer ]

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

The tracing infrastructure allows for recursion. That is, an interrupt
may interrupt the act of tracing an event, and that interrupt may very well
perform its own trace. This is a recursive trace, and is fine to do.

The problem arises when there is a bug, and the utility doing the trace
calls something that recurses back into the tracer. This recursion is not
caused by an external event like an interrupt, but by code that is not
expected to recurse. The result could be a lockup.

This patch adds a bitmask to the task structure that keeps track
of the trace recursion. To find the interrupt depth, the following
algorithm is used:

  level = hardirq_count() + softirq_count() + in_nmi;

Here, level will be the depth of interrutps and softirqs, and even handles
the nmi. Then the corresponding bit is set in the recursion bitmask.
If the bit was already set, we know we had a recursion at the same level
and we warn about it and fail the writing to the buffer.

After the data has been committed to the buffer, we clear the bit.
No atomics are needed. The only races are with interrupts and they reset
the bitmask before returning anywy.

[ Impact: detect same irq level trace recursion ]
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>