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  1. Mar 15, 2019
  3. Mar 13, 2019
    • Douglas Anderson's avatar
      tracing: kdb: Fix ftdump to not sleep · 31b265b3
      Douglas Anderson authored 
      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/20161117191605.GA21459@google.com

Link: http://lkml.kernel.org/r/20190308193205.213659-1-dianders@chromium.org



Reported-by: default avatarBrian Norris <briannorris@chromium.org>
Signed-off-by: default avatarDouglas Anderson <dianders@chromium.org>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
      31b265b3
  5. Mar 12, 2019
  7. Mar 06, 2019
  9. Mar 05, 2019
  11. Feb 21, 2019
  13. Feb 16, 2019
    • Elena Reshetova's avatar
      uprobes: convert uprobe.ref to refcount_t · ce59b8e9
      Elena Reshetova authored 
      atomic_t variables are currently used to implement reference
counters with the following properties:
 - counter is initialized to 1 using atomic_set()
 - a resource is freed upon counter reaching zero
 - once counter reaches zero, its further
   increments aren't allowed
 - counter schema uses basic atomic operations
   (set, inc, inc_not_zero, dec_and_test, etc.)

Such atomic variables should be converted to a newly provided
refcount_t type and API that prevents accidental counter overflows
and underflows. This is important since overflows and underflows
can lead to use-after-free situation and be exploitable.

The variable uprobe.ref is used as pure reference counter.
Convert it to refcount_t and fix up the operations.

**Important note for maintainers:

Some functions from refcount_t API defined in lib/refcount.c
have different memory ordering guarantees than their atomic
counterparts.
The full comparison can be seen in
https://lkml.org/lkml/2017/11/15/57 and it is hopefully soon
in state to be merged to the documentation tree.
Normally the differences should not matter since refcount_t provides
enough guarantees to satisfy the refcounting use cases, but in
some rare cases it might matter.
Please double check that you don't have some undocumented
memory guarantees for this variable usage.

For the uprobe.ref it might make a difference
in following places:
 - put_uprobe(): decrement in refcount_dec_and_test() only
   provides RELEASE ordering and control dependency on success
   vs. fully ordered atomic counterpart

Link: http://lkml.kernel.org/r/1547637627-29526-1-git-send-email-elena.reshetova@intel.com



Suggested-by: default avatarKees Cook <keescook@chromium.org>
Acked-by: default avatarOleg Nesterov <oleg@redhat.com>
Reviewed-by: default avatarDavid Windsor <dwindsor@gmail.com>
Reviewed-by: default avatarHans Liljestrand <ishkamiel@gmail.com>
Reviewed-by: default avatarSrikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: default avatarElena Reshetova <elena.reshetova@intel.com>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
      ce59b8e9
    • Steven Rostedt (VMware)'s avatar
      ftrace: Allow enabling of filters via index of available_filter_functions · f79b3f33
      Steven Rostedt (VMware) authored 
      

Enabling of large number of functions by echoing in a large subset of the
functions in available_filter_functions can take a very long time. The
process requires testing all functions registered by the function tracer
(which is in the 10s of thousands), and doing a kallsyms lookup to convert
the ip address into a name, then comparing that name with the string passed
in.

When a function causes the function tracer to crash the system, a binary
bisect of the available_filter_functions can be done to find the culprit.
But this requires passing in half of the functions in
available_filter_functions over and over again, which makes it basically a
O(n^2) operation. With 40,000 functions, that ends up bing 1,600,000,000
opertions! And enabling this can take over 20 minutes.

As a quick speed up, if a number is passed into one of the filter files,
instead of doing a search, it just enables the function at the corresponding
line of the available_filter_functions file. That is:

 # echo 50 > set_ftrace_filter
 # cat set_ftrace_filter
 x86_pmu_commit_txn

 # head -50 available_filter_functions | tail -1
 x86_pmu_commit_txn

This allows setting of half the available_filter_functions to take place in
less than a second!

 # time seq 20000 > set_ftrace_filter
 real    0m0.042s
 user    0m0.005s
 sys     0m0.015s

 # wc -l set_ftrace_filter
 20000 set_ftrace_filter

Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
      f79b3f33
  15. Feb 12, 2019
    • Changbin Du's avatar
      tracing: Change the function format to display function names by perf · 85acbb21
      Changbin Du authored 
      Here is an example for this change.

$ sudo perf record -e 'ftrace:function' --filter='ip==schedule'
$ sudo perf report

The output of perf before this patch:

\# Samples: 100  of event 'ftrace:function'
\# Event count (approx.): 100
\#
\# Overhead  Trace output
\# ........  ......................................
\#
    51.00%   ffffffff81f6aaa0 <-- ffffffff81158e8d
    29.00%   ffffffff81f6aaa0 <-- ffffffff8116ccb2
     8.00%   ffffffff81f6aaa0 <-- ffffffff81f6f2ed
     4.00%   ffffffff81f6aaa0 <-- ffffffff811628db
     4.00%   ffffffff81f6aaa0 <-- ffffffff81f6ec5b
     2.00%   ffffffff81f6aaa0 <-- ffffffff81f6f21a
     1.00%   ffffffff81f6aaa0 <-- ffffffff811b04af
     1.00%   ffffffff81f6aaa0 <-- ffffffff8143ce17

After this patch:

\# Samples: 36  of event 'ftrace:function'
\# Event count (approx.): 36
\#
\# Overhead  Trace output
\# ........  ............................................
\#
    38.89%   schedule <-- schedule_hrtimeout_range_clock
    27.78%   schedule <-- worker_thread
    13.89%   schedule <-- schedule_timeout
    11.11%   schedule <-- smpboot_thread_fn
     5.56%   schedule <-- rcu_gp_kthread
     2.78%   schedule <-- exit_to_usermode_loop

Link: http://lkml.kernel.org/r/20190209161919.32350-1-changbin.du@gmail.com



Signed-off-by: default avatarChangbin Du <changbin.du@gmail.com>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
      85acbb21
  17. Feb 07, 2019