tracing: Have persistent trace instances save KASLR offset

There's no reason to save the KASLR offset for the ring buffer itself.
That is used by the tracer. Now that the tracer has a way to save da

tracing: Have persistent trace instances save KASLR offset

There's no reason to save the KASLR offset for the ring buffer itself.
That is used by the tracer. Now that the tracer has a way to save data in
the persistent memory of the ring buffer, have the tracing infrastructure
take care of the saving of the KASLR offset.

Cc: Mark Rutland <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Andrew Morton <[email protected]>
Link: https://lore.kernel.org/[email protected]
Reviewed-by: Masami Hiramatsu (Google) <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>

show more ...

ring-buffer: Add ring_buffer_meta_scratch()

Now that there's one meta data at the start of the persistent memory used by
the ring buffer, allow the caller to request some memory right after that
dat

ring-buffer: Add ring_buffer_meta_scratch()

Now that there's one meta data at the start of the persistent memory used by
the ring buffer, allow the caller to request some memory right after that
data that it can use as its own persistent memory.

Also fix some white space issues with ring_buffer_alloc().

Cc: Mark Rutland <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Andrew Morton <[email protected]>
Link: https://lore.kernel.org/[email protected]
Reviewed-by: Masami Hiramatsu (Google) <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>

show more ...

ring-buffer: Use kaslr address instead of text delta

Instead of saving off the text and data pointers and using them to compare
with the current boot's text and data pointers, just save off the KASL

ring-buffer: Use kaslr address instead of text delta

Instead of saving off the text and data pointers and using them to compare
with the current boot's text and data pointers, just save off the KASLR
offset. Then that can be used to figure out how to read the previous boots
buffer.

The last_boot_info will now show this offset, but only if it is for a
previous boot:

~# cat instances/boot_mapped/last_boot_info
39000000 [kernel]

~# echo function > instances/boot_mapped/current_tracer
~# cat instances/boot_mapped/last_boot_info
# Current

If the KASLR offset saved is for the current boot, the last_boot_info will
show the value of "current".

Cc: Mark Rutland <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Andrew Morton <[email protected]>
Link: https://lore.kernel.org/[email protected]
Reviewed-by: Masami Hiramatsu (Google) <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>

show more ...

ring-buffer: Remove unused function ring_buffer_nr_pages()

Because ring_buffer_nr_pages() is not an inline function and user accesses
buffer->buffers[cpu]->nr_pages directly, the function ring_buffe

ring-buffer: Remove unused function ring_buffer_nr_pages()

Because ring_buffer_nr_pages() is not an inline function and user accesses
buffer->buffers[cpu]->nr_pages directly, the function ring_buffer_nr_pages
is removed.

Signed-off-by: Jianhui Zhou <[email protected]>
Link: https://lore.kernel.org/[email protected]
Signed-off-by: Steven Rostedt (Google) <[email protected]>

show more ...

tracing/ring-buffer: Add last_boot_info file to boot instance

If an instance is mapped to memory on boot up, create a new file called
"last_boot_info" that will hold information that can be used to

tracing/ring-buffer: Add last_boot_info file to boot instance

If an instance is mapped to memory on boot up, create a new file called
"last_boot_info" that will hold information that can be used to properly
parse the raw data in the ring buffer.

It will export the delta of the addresses for text and data from what it
was from the last boot. It does not expose actually addresses (unless you
knew what the actual address was from the last boot).

The output will look like:

# cat last_boot_info
text delta: -268435456
data delta: -268435456

The text and data are kept separate in case they are ever made different.

Link: https://lkml.kernel.org/r/[email protected]

Cc: Masami Hiramatsu <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Vincent Donnefort <[email protected]>
Cc: Joel Fernandes <[email protected]>
Cc: Daniel Bristot de Oliveira <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vineeth Pillai <[email protected]>
Cc: Youssef Esmat <[email protected]>
Cc: Beau Belgrave <[email protected]>
Cc: Alexander Graf <[email protected]>
Cc: Baoquan He <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: "Paul E. McKenney" <[email protected]>
Cc: David Howells <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Tony Luck <[email protected]>
Cc: Guenter Roeck <[email protected]>
Cc: Ross Zwisler <[email protected]>
Cc: Kees Cook <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>

show more ...

ring-buffer: Add ring_buffer_alloc_range()

In preparation to allowing the trace ring buffer to be allocated in a
range of memory that is persistent across reboots, add
ring_buffer_alloc_range(). It

ring-buffer: Add ring_buffer_alloc_range()

In preparation to allowing the trace ring buffer to be allocated in a
range of memory that is persistent across reboots, add
ring_buffer_alloc_range(). It takes a contiguous range of memory and will
split it up evenly for the per CPU ring buffers.

If there's not enough memory to handle all CPUs with the minimum size, it
will fail to allocate the ring buffer.

Link: https://lkml.kernel.org/r/[email protected]

Cc: Masami Hiramatsu <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Vincent Donnefort <[email protected]>
Cc: Joel Fernandes <[email protected]>
Cc: Daniel Bristot de Oliveira <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vineeth Pillai <[email protected]>
Cc: Youssef Esmat <[email protected]>
Cc: Beau Belgrave <[email protected]>
Cc: Alexander Graf <[email protected]>
Cc: Baoquan He <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: "Paul E. McKenney" <[email protected]>
Cc: David Howells <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Tony Luck <[email protected]>
Cc: Guenter Roeck <[email protected]>
Cc: Ross Zwisler <[email protected]>
Cc: Kees Cook <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>

show more ...

ring-buffer: Introducing ring-buffer mapping functions

In preparation for allowing the user-space to map a ring-buffer, add
a set of mapping functions:

ring_buffer_{map,unmap}()

And controls on

ring-buffer: Introducing ring-buffer mapping functions

In preparation for allowing the user-space to map a ring-buffer, add
a set of mapping functions:

ring_buffer_{map,unmap}()

And controls on the ring-buffer:

ring_buffer_map_get_reader() /* swap reader and head */

Mapping the ring-buffer also involves:

A unique ID for each subbuf of the ring-buffer, currently they are
only identified through their in-kernel VA.

A meta-page, where are stored ring-buffer statistics and a
description for the current reader

The linear mapping exposes the meta-page, and each subbuf of the
ring-buffer, ordered following their unique ID, assigned during the
first mapping.

Once mapped, no subbuf can get in or out of the ring-buffer: the buffer
size will remain unmodified and the splice enabling functions will in
reality simply memcpy the data instead of swapping subbufs.

Link: https://lore.kernel.org/linux-trace-kernel/[email protected]

CC: <[email protected]>
Signed-off-by: Vincent Donnefort <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>

show more ...

tracing/ring-buffer: Fix wait_on_pipe() race

When the trace_pipe_raw file is closed, there should be no new readers on
the file descriptor. This is mostly handled with the waking and wait_index
fiel

tracing/ring-buffer: Fix wait_on_pipe() race

When the trace_pipe_raw file is closed, there should be no new readers on
the file descriptor. This is mostly handled with the waking and wait_index
fields of the iterator. But there's still a slight race.

CPU 0 CPU 1
----- -----
wait_index++;
index = wait_index;
ring_buffer_wake_waiters();
wait_on_pipe()
ring_buffer_wait();

The ring_buffer_wait() will miss the wakeup from CPU 1. The problem is
that the ring_buffer_wait() needs the logic of:

prepare_to_wait();
if (!condition)
schedule();

Where the missing condition check is the iter->wait_index update.

Have the ring_buffer_wait() take a conditional callback function and a
data parameter that can be used within the wait_event_interruptible() of
the ring_buffer_wait() function.

In wait_on_pipe(), pass a condition function that will check if the
wait_index has been updated, if it has, it will return true to break out
of the wait_event_interruptible() loop.

Create a new field "closed" in the trace_iterator and set it in the
.flush() callback before calling ring_buffer_wake_waiters().
This will keep any new readers from waiting on a closed file descriptor.

Have the wait_on_pipe() condition callback also check the closed field.

Change the wait_index field of the trace_iterator to atomic_t. There's no
reason it needs to be 'long' and making it atomic and using
atomic_read_acquire() and atomic_fetch_inc_release() will provide the
necessary memory barriers.

Add a "woken" flag to tracing_buffers_splice_read() to exit the loop after
one more try to fetch data. That is, if it waited for data and something
woke it up, it should try to collect any new data and then exit back to
user space.

Link: https://lore.kernel.org/linux-trace-kernel/CAHk-=wgsNgewHFxZAJiAQznwPMqEtQmi1waeS2O1v6L4c_Um5A@mail.gmail.com/
Link: https://lore.kernel.org/linux-trace-kernel/[email protected]

Cc: [email protected]
Cc: Masami Hiramatsu <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: linke li <[email protected]>
Cc: Rabin Vincent <[email protected]>
Fixes: f3ddb74ad0790 ("tracing: Wake up ring buffer waiters on closing of the file")
Signed-off-by: Steven Rostedt (Google) <[email protected]>

show more ...

ring-buffer: Use wait_event_interruptible() in ring_buffer_wait()

Convert ring_buffer_wait() over to wait_event_interruptible(). The default
condition is to execute the wait loop inside __wait_event

ring-buffer: Use wait_event_interruptible() in ring_buffer_wait()

Convert ring_buffer_wait() over to wait_event_interruptible(). The default
condition is to execute the wait loop inside __wait_event() just once.

This does not change the ring_buffer_wait() prototype yet, but
restructures the code so that it can take a "cond" and "data" parameter
and will call wait_event_interruptible() with a helper function as the
condition.

The helper function (rb_wait_cond) takes the cond function and data
parameters. It will first check if the buffer hit the watermark defined by
the "full" parameter and then call the passed in condition parameter. If
either are true, it returns true.

If rb_wait_cond() does not return true, it will set the appropriate
"waiters_pending" flag and returns false.

Link: https://lore.kernel.org/linux-trace-kernel/CAHk-=wgsNgewHFxZAJiAQznwPMqEtQmi1waeS2O1v6L4c_Um5A@mail.gmail.com/
Link: https://lore.kernel.org/linux-trace-kernel/[email protected]

Cc: [email protected]
Cc: Masami Hiramatsu <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: linke li <[email protected]>
Cc: Rabin Vincent <[email protected]>
Fixes: f3ddb74ad0790 ("tracing: Wake up ring buffer waiters on closing of the file")
Signed-off-by: Steven Rostedt (Google) <[email protected]>

show more ...

ring-buffer: Read and write to ring buffers with custom sub buffer size

As the size of the ring sub buffer page can be changed dynamically,
the logic that reads and writes to the buffer should be fi

ring-buffer: Read and write to ring buffers with custom sub buffer size

As the size of the ring sub buffer page can be changed dynamically,
the logic that reads and writes to the buffer should be fixed to take
that into account. Some internal ring buffer APIs are changed:
ring_buffer_alloc_read_page()
ring_buffer_free_read_page()
ring_buffer_read_page()
A new API is introduced:
ring_buffer_read_page_data()

Link: https://lore.kernel.org/linux-trace-devel/[email protected]
Link: https://lore.kernel.org/linux-trace-kernel/[email protected]

Cc: Masami Hiramatsu <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Vincent Donnefort <[email protected]>
Cc: Kent Overstreet <[email protected]>
Signed-off-by: Tzvetomir Stoyanov (VMware) <[email protected]>
[ Fixed kerneldoc on data_page parameter in ring_buffer_free_read_page() ]
Signed-off-by: Steven Rostedt (Google) <[email protected]>

show more ...

ring-buffer: Add interface for configuring trace sub buffer size

The trace ring buffer sub page size can be configured, per trace
instance. A new ftrace file "buffer_subbuf_order" is added to get an

ring-buffer: Add interface for configuring trace sub buffer size

The trace ring buffer sub page size can be configured, per trace
instance. A new ftrace file "buffer_subbuf_order" is added to get and
set the size of the ring buffer sub page for current trace instance.
The size must be an order of system page size, that's why the new
interface works with system page order, instead of absolute page size:
0 means the ring buffer sub page is equal to 1 system page and so
forth:
0 - 1 system page
1 - 2 system pages
2 - 4 system pages
...
The ring buffer sub page size is limited between 1 and 128 system
pages. The default value is 1 system page.
New ring buffer APIs are introduced:
ring_buffer_subbuf_order_set()
ring_buffer_subbuf_order_get()
ring_buffer_subbuf_size_get()

Link: https://lore.kernel.org/linux-trace-devel/[email protected]
Link: https://lore.kernel.org/linux-trace-kernel/[email protected]

Cc: Masami Hiramatsu <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Vincent Donnefort <[email protected]>
Cc: Kent Overstreet <[email protected]>
Signed-off-by: Tzvetomir Stoyanov (VMware) <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>

show more ...

ring-buffer: Page size per ring buffer

Currently the size of one sub buffer page is global for all buffers and
it is hard coded to one system page. In order to introduce configurable
ring buffer sub

ring-buffer: Page size per ring buffer

Currently the size of one sub buffer page is global for all buffers and
it is hard coded to one system page. In order to introduce configurable
ring buffer sub page size, the internal logic should be refactored to
work with sub page size per ring buffer.

Link: https://lore.kernel.org/linux-trace-devel/[email protected]
Link: https://lore.kernel.org/linux-trace-kernel/[email protected]

Cc: Masami Hiramatsu <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Vincent Donnefort <[email protected]>
Cc: Kent Overstreet <[email protected]>
Signed-off-by: Tzvetomir Stoyanov (VMware) <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>

show more ...

tracing: Allow for max buffer data size trace_marker writes

Allow a trace write to be as big as the ring buffer tracing data will
allow. Currently, it only allows writes of 1KB in size, but there's

tracing: Allow for max buffer data size trace_marker writes

Allow a trace write to be as big as the ring buffer tracing data will
allow. Currently, it only allows writes of 1KB in size, but there's no
reason that it cannot allow what the ring buffer can hold.

Link: https://lore.kernel.org/linux-trace-kernel/[email protected]

Cc: Masami Hiramatsu <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>

show more ...

ring_buffer: Remove unused "event" parameter

After commit a389d86f7fd0 ("ring-buffer: Have nested events still record
running time stamp"), the "event" parameter is no longer used in either
ring_buf

ring_buffer: Remove unused "event" parameter

After commit a389d86f7fd0 ("ring-buffer: Have nested events still record
running time stamp"), the "event" parameter is no longer used in either
ring_buffer_unlock_commit() or rb_commit(). Best to remove it.

Link: https://lkml.kernel.org/r/[email protected]

Signed-off-by: Song Chen <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>

show more ...

tracing/ring-buffer: Have polling block on watermark

Currently the way polling works on the ring buffer is broken. It will
return immediately if there's any data in the ring buffer whereas a read
wi

tracing/ring-buffer: Have polling block on watermark

Currently the way polling works on the ring buffer is broken. It will
return immediately if there's any data in the ring buffer whereas a read
will block until the watermark (defined by the tracefs buffer_percent file)
is hit.

That is, a select() or poll() will return as if there's data available,
but then the following read will block. This is broken for the way
select()s and poll()s are supposed to work.

Have the polling on the ring buffer also block the same way reads and
splice does on the ring buffer.

Link: https://lkml.kernel.org/r/[email protected]

Cc: Linux Trace Kernel <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Primiano Tucci <[email protected]>
Cc: [email protected]
Fixes: 1e0d6714aceb7 ("ring-buffer: Do not wake up a splice waiter when page is not full")
Signed-off-by: Steven Rostedt (Google) <[email protected]>

show more ...

ring-buffer: Add ring_buffer_wake_waiters()

On closing of a file that represents a ring buffer or flushing the file,
there may be waiters on the ring buffer that needs to be woken up and exit
the ri

ring-buffer: Add ring_buffer_wake_waiters()

On closing of a file that represents a ring buffer or flushing the file,
there may be waiters on the ring buffer that needs to be woken up and exit
the ring_buffer_wait() function.

Add ring_buffer_wake_waiters() to wake up the waiters on the ring buffer
and allow them to exit the wait loop.

Link: https://lkml.kernel.org/r/[email protected]

Cc: [email protected]
Cc: Ingo Molnar <[email protected]>
Cc: Andrew Morton <[email protected]>
Fixes: 15693458c4bc0 ("tracing/ring-buffer: Move poll wake ups into ring buffer code")
Signed-off-by: Steven Rostedt (Google) <[email protected]>

show more ...

tracing: Remove unused argument from "ring_buffer_time_stamp()

The "cpu" parameter is not being used by the function.

Link: https://lkml.kernel.org/r/[email protected]

Sig

tracing: Remove unused argument from "ring_buffer_time_stamp()

The "cpu" parameter is not being used by the function.

Link: https://lkml.kernel.org/r/[email protected]

Signed-off-by: Yordan Karadzhov (VMware) <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>

show more ...

ring-buffer: Allow ring_buffer_event_time_stamp() to return time stamp of all events

Currently, ring_buffer_event_time_stamp() only returns an accurate time
stamp of the event if it has an absolute

ring-buffer: Allow ring_buffer_event_time_stamp() to return time stamp of all events

Currently, ring_buffer_event_time_stamp() only returns an accurate time
stamp of the event if it has an absolute extended time stamp attached to
it. To make it more robust, use the event_stamp() in case the event does
not have an absolute value attached to it.

This will allow ring_buffer_event_time_stamp() to be used in more cases
than just histograms, and it will also allow histograms to not require
including absolute values all the time.

Link: https://lkml.kernel.org/r/[email protected]

Reviewed-by: Tom Zanussi <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>

show more ...

ring-buffer: speed up buffer resets by avoiding synchronize_rcu for each CPU

On a 144 thread system, `perf ftrace` takes about 20 seconds to start
up, due to calling synchronize_rcu() for each CPU.

ring-buffer: speed up buffer resets by avoiding synchronize_rcu for each CPU

On a 144 thread system, `perf ftrace` takes about 20 seconds to start
up, due to calling synchronize_rcu() for each CPU.

cat /proc/108560/stack
0xc0003e7eb336f470
__switch_to+0x2e0/0x480
__wait_rcu_gp+0x20c/0x220
synchronize_rcu+0x9c/0xc0
ring_buffer_reset_cpu+0x88/0x2e0
tracing_reset_online_cpus+0x84/0xe0
tracing_open+0x1d4/0x1f0

On a system with 10x more threads, it starts to become an annoyance.

Batch these up so we disable all the per-cpu buffers first, then
synchronize_rcu() once, then reset each of the buffers. This brings
the time down to about 0.5s.

Link: https://lkml.kernel.org/r/[email protected]

Tested-by: Anton Blanchard <[email protected]>
Acked-by: Paul E. McKenney <[email protected]>
Signed-off-by: Nicholas Piggin <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>

show more ...

ring-buffer/tracing: Have iterator acknowledge dropped events

Have the ring_buffer_iterator set a flag if events were dropped as it were
to go and peek at the next event. Have the trace file display

ring-buffer/tracing: Have iterator acknowledge dropped events

Have the ring_buffer_iterator set a flag if events were dropped as it were
to go and peek at the next event. Have the trace file display this fact if
it happened with a "LOST EVENTS" message.

Link: http://lkml.kernel.org/r/[email protected]

Signed-off-by: Steven Rostedt (VMware) <[email protected]>

show more ...

ring-buffer: Rename ring_buffer_read() to read_buffer_iter_advance()

When the ring buffer was first created, the iterator followed the normal
producer/consumer operations where it had both a peek()

ring-buffer: Rename ring_buffer_read() to read_buffer_iter_advance()

When the ring buffer was first created, the iterator followed the normal
producer/consumer operations where it had both a peek() operation, that just
returned the event at the current location, and a read(), that would return
the event at the current location and also increment the iterator such that
the next peek() or read() will return the next event.

The only use of the ring_buffer_read() is currently to move the iterator to
the next location and nothing now actually reads the event it returns.
Rename this function to its actual use case to ring_buffer_iter_advance(),
which also adds the "iter" part to the name, which is more meaningful. As
the timestamp returned by ring_buffer_read() was never used, there's no
reason that this new version should bother having returning it. It will also
become a void function.

Link: http://lkml.kernel.org/r/[email protected]

Signed-off-by: Steven Rostedt (VMware) <[email protected]>

show more ...

tracing: Make struct ring_buffer less ambiguous

As there's two struct ring_buffers in the kernel, it causes some confusion.
The other one being the perf ring buffer. It was agreed upon that as neith

tracing: Make struct ring_buffer less ambiguous

As there's two struct ring_buffers in the kernel, it causes some confusion.
The other one being the perf ring buffer. It was agreed upon that as neither
of the ring buffers are generic enough to be used globally, they should be
renamed as:

perf's ring_buffer -> perf_buffer
ftrace's ring_buffer -> trace_buffer

This implements the changes to the ring buffer that ftrace uses.

Link: https://lore.kernel.org/r/[email protected]

Signed-off-by: Steven Rostedt (VMware) <[email protected]>

show more ...

tracing: kdb: Fix ftdump to not sleep

As reported back in 2016-11 [1], the "ftdump" kdb command triggers a
BUG for "sleeping function called from invalid context".

kdb's "ftdump" command wants to c

tracing: kdb: Fix ftdump to not sleep

As reported back in 2016-11 [1], the "ftdump" kdb command triggers a
BUG for "sleeping function called from invalid context".

kdb's "ftdump" command wants to call ring_buffer_read_prepare() in
atomic context. A very simple solution for this is to add allocation
flags to ring_buffer_read_prepare() so kdb can call it without
triggering the allocation error. This patch does that.

Note that in the original email thread about this, it was suggested
that perhaps the solution for kdb was to either preallocate the buffer
ahead of time or create our own iterator. I'm hoping that this
alternative of adding allocation flags to ring_buffer_read_prepare()
can be considered since it means I don't need to duplicate more of the
core trace code into "trace_kdb.c" (for either creating my own
iterator or re-preparing a ring allocator whose memory was already
allocated).

NOTE: another option for kdb is to actually figure out how to make it
reuse the existing ftrace_dump() function and totally eliminate the
duplication. This sounds very appealing and actually works (the "sr
z" command can be seen to properly dump the ftrace buffer). The
downside here is that ftrace_dump() fully consumes the trace buffer.
Unless that is changed I'd rather not use it because it means "ftdump
| grep xyz" won't be very useful to search the ftrace buffer since it
will throw away the whole trace on the first grep. A future patch to
dump only the last few lines of the buffer will also be hard to
implement.

[1] https://lkml.kernel.org/r/[email protected]

Link: http://lkml.kernel.org/r/[email protected]

Reported-by: Brian Norris <[email protected]>
Signed-off-by: Douglas Anderson <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>

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ring-buffer: Remove unused function ring_buffer_page_len()

Commit 6b7e633fe9c2 ("tracing: Remove extra zeroing out of the ring
buffer page") removed the only caller of ring_buffer_page_len(). The
fu

ring-buffer: Remove unused function ring_buffer_page_len()

Commit 6b7e633fe9c2 ("tracing: Remove extra zeroing out of the ring
buffer page") removed the only caller of ring_buffer_page_len(). The
function is now unused and may be removed.

Link: http://lkml.kernel.org/r/[email protected]

Signed-off-by: Miroslav Benes <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>

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ring-buffer: Add percentage of ring buffer full to wake up reader

Instead of just waiting for a page to be full before waking up a pending
reader, allow the reader to pass in a "percentage" of pages

ring-buffer: Add percentage of ring buffer full to wake up reader

Instead of just waiting for a page to be full before waking up a pending
reader, allow the reader to pass in a "percentage" of pages that have
content before waking up a reader. This should help keep the process of
reading the events not cause wake ups that constantly cause reading of the
buffer.

Signed-off-by: Steven Rostedt (VMware) <[email protected]>

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