- Fix several tracefs files that did not take the trace_array reference
A trace instance can be created and destroyed in the tracefs "instances"
directory via mkdir and rmdir respectively. The instance is represented by
a trace_array descriptor. Most tracefs files pass the trace_array as the
private data of the inode to the open/read/write functions. Since there is
no locking between the time a task opens a file and the deletion of the
instance (and the freeing of the trace_array), each open needs to get a
reference to the trace_array and each close must remove it. A instance
can't be removed if there's any reference taken on its trace_array. The
open function uses trace_array_get() that takes a lock (preventing removal
of instances) and iterates the list of all existing trace_arrays and if it
finds a match, it takes the reference and releases the lock. If it doesn't
find a match, it causes the open to return -ENODEV.
There were some added files that did not take the trace_array reference
on open that needed to be fixed. Sashiko also correctly pointed out that
there were some files that took an address of an field or element of the
trace_array which had a pointer back to the trace_array to take its
reference on open. But this leaves a slight race between referencing this
element to get the trace_array as the element itself could be freed. To
solve this, some helper functions were created to look for trace_arrays
with this field or element in the search so that the element did not have
to be dereferenced before the trace_array's reference was taken.
- Add a lock around ftrace_ops initialization
When a ftrace_ops is first used by ftrace, some internal initialization is
performed on the ops. But if multiple tasks were calling functions that
did this initialization, it could race and perform doing the
initialization more than once, corrupting the internal data. Add a lock in
the initialization code to prevent this from happening.
- Fix splice reads on mmapped buffers
The logic in the ring buffer splice code for mmapped buffers is supposed
to do a copy of the memory as the mapped buffers can't be given to splice.
But there was an if statement within the copy code that would return a -1
if a request for a full page was done and it wasn't a partial read. This
is because this logic was written before mmapped buffers existed and this
case didn't make sense at the time. For mmapped buffers it makes perfect
sense and by returning early can drop a lot of pages unnecessarily.
- Have the persistent ring buffer validation check nr_subbufs
Sashiko reported that the validation code was relying on the saved
nr_subbufs to match the calculated nr_pages + 1 and if they were off, that
the code could cause corruption. Sashiko is correct, and the saved
nr_subbufs should be validated before assuming it is correct.
- Do not allow more than one instance with the same name on cmdline
If an admin were to add more than one trace instances with the same name
they all would be created, but only the first one would be accessible via
tracefs. This used to not be allowed but some restructuring of code has
since made it possible.
- Fix the race between subbuf resize and trace_pipe_raw readers
If a task was reading trace_pipe_raw while another task was changing the
ring buffer subbuf size, it could crash the reader. The trace_pipe_raw
readers do get their own copy of the page from the buffer, but the code
needs some restructuring to not have the resize of the subbuffers cause
issues.
- Cap the size of the mapped (static) ring buffer nr_pages
The meta data used for ring buffer mapped buffers is 32 bit in size. A
normal ring buffer could (in theory) have more than 4 billion pages.
But this is not allowed by mapped buffers, so enforce it.
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Merge tag 'trace-v7.3-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace
Pull tracing fixes from Steven Rostedt:
- Fix several tracefs files that did not take the trace_array reference
A trace instance can be created and destroyed in the tracefs
"instances" directory via mkdir and rmdir respectively. The instance
is represented by a trace_array descriptor.
Most tracefs files pass the trace_array as the private data of the
inode to the open/read/write functions. Since there is no locking
between the time a task opens a file and the deletion of the instance
(and the freeing of the trace_array), each open needs to get a
reference to the trace_array and each close must remove it.
An instance can't be removed if there's any reference taken on its
trace_array. The open function uses trace_array_get() that takes a
lock (preventing removal of instances) and iterates the list of all
existing trace_arrays and if it finds a match, it takes the reference
and releases the lock. If it doesn't find a match, it causes the open
to return -ENODEV.
There were some added files that did not take the trace_array
reference on open that needed to be fixed. Sashiko also correctly
pointed out that there were some files that took an address of an
field or element of the trace_array which had a pointer back to the
trace_array to take its reference on open. But this leaves a slight
race between referencing this element to get the trace_array as the
element itself could be freed. To solve this, some helper functions
were created to look for trace_arrays with this field or element in
the search so that the element did not have to be dereferenced before
the trace_array's reference was taken.
- Add a lock around ftrace_ops initialization
When a ftrace_ops is first used by ftrace, some internal
initialization is performed on the ops. But if multiple tasks were
calling functions that did this initialization, it could race and
perform doing the initialization more than once, corrupting the
internal data. Add a lock in the initialization code to prevent this
from happening.
- Fix splice reads on mmapped buffers
The logic in the ring buffer splice code for mmapped buffers is
supposed to do a copy of the memory as the mapped buffers can't be
given to splice. But there was an if statement within the copy code
that would return a -1 if a request for a full page was done and it
wasn't a partial read. This is because this logic was written before
mmapped buffers existed and this case didn't make sense at the time.
For mmapped buffers it makes perfect sense and by returning early can
drop a lot of pages unnecessarily.
- Have the persistent ring buffer validation check nr_subbufs
Sashiko reported that the validation code was relying on the saved
nr_subbufs to match the calculated nr_pages + 1 and if they were off,
that the code could cause corruption. Sashiko is correct, and the
saved nr_subbufs should be validated before assuming it is correct.
- Do not allow more than one instance with the same name on cmdline
If an admin were to add more than one trace instances with the same
name they all would be created, but only the first one would be
accessible via tracefs. This used to not be allowed but some
restructuring of code has since made it possible.
- Fix the race between subbuf resize and trace_pipe_raw readers
If a task was reading trace_pipe_raw while another task was changing
the ring buffer subbuf size, it could crash the reader. The
trace_pipe_raw readers do get their own copy of the page from the
buffer, but the code needs some restructuring to not have the resize
of the subbuffers cause issues.
- Cap the size of the mapped (static) ring buffer nr_pages
The meta data used for ring buffer mapped buffers is 32 bit in size.
A normal ring buffer could (in theory) have more than 4 billion
pages. But this is not allowed by mapped buffers, so enforce it.
* tag 'trace-v7.3-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
ring-buffer: Use a macro for static buffer bits
tracing: Fix comment in tracing_buffers_splice_read()
ring-buffer: Prevent truncation of nr_pages / nr_subbufs
ring-buffer: Cap static ring buffer nr_pages
tracing: Fix subbuf resize races with trace_pipe_raw readers
tracing: Fix to avoid creating trace instances with duplicate names
ring-buffer: Add checking nr_subbufs to persistent ring buffer validation
ring-buffer: Allow splice reads on static buffers
tracing: Take trace_array reference when opening options file
ftrace: Synchronize the initialization of ftrace_ops
ftrace: Take trace_array reference before accessing its ftrace_ops
tracing: Have show_event_filters/triggers files take trace array ref
