linux-toradex.git/kernel/hw_breakpoint.c, branch v2.6.37.2

perf,hw_breakpoint: Initialize hardware api earlier

2010-11-12T13:51:55+00:00

When using early debugging, the kernel does not initialize the
hw_breakpoint API early enough and causes the late initialization of
the kernel debugger to fail. The boot arguments are:

    earlyprintk=vga ekgdboc=kbd kgdbwait

Then simply type "go" at the kdb prompt and boot. The kernel will
later emit the message:

    kgdb: Could not allocate hwbreakpoints

And at that point the kernel debugger will cease to work correctly.

The solution is to initialize the hw_breakpoint at the same time that
all the other perf call backs are initialized instead of using a
core_initcall() initialization which happens well after the kernel
debugger can make use of hardware breakpoints.

Signed-off-by: Jason Wessel 
CC: Frederic Weisbecker 
CC: Ingo Molnar 
CC: Peter Zijlstra 
LKML-Reference: <4CD3396D.1090308@windriver.com>
Signed-off-by: Frederic Weisbecker

perf, hw_breakpoint: Fix crash in hw_breakpoint creation

2010-10-18T17:58:55+00:00

hw_breakpoint creation needs to account stuff per-task to ensure there
is always sufficient hardware resources to back these things due to
ptrace.

With the perf per pmu context changes the event initialization no
longer has access to the event context, for the simple reason that we
need to first find the pmu (result of initialization) before we can
find the context.

This makes hw_breakpoints unhappy, because it can no longer do per
task accounting, cure this by frobbing a task pointer in the event::hw
bits for now...

Signed-off-by: Peter Zijlstra 
Cc: Frederic Weisbecker 
LKML-Reference: <20101014203625.391543667@chello.nl>
Signed-off-by: Ingo Molnar

perf events: Clean up pid passing

2010-09-15T08:44:00+00:00

The kernel perf event creation path shouldn't use find_task_by_vpid()
because a vpid exists in a specific namespace. find_task_by_vpid() uses
current's pid namespace which isn't always the correct namespace to use
for the vpid in all the places perf_event_create_kernel_counter() (and
thus find_get_context()) is called.

The goal is to clean up pid namespace handling and prevent bugs like:

	https://bugzilla.kernel.org/show_bug.cgi?id=17281

Instead of using pids switch find_get_context() to use task struct
pointers directly. The syscall is responsible for resolving the pid to
a task struct. This moves the pid namespace resolution into the syscall
much like every other syscall that takes pid parameters.

Signed-off-by: Matt Helsley 
Signed-off-by: Peter Zijlstra 
Cc: Robin Green 
Cc: Prasad 
Cc: Arnaldo Carvalho de Melo 
Cc: Steven Rostedt 
Cc: Will Deacon 
Cc: Mahesh Salgaonkar 
LKML-Reference: 
Signed-off-by: Ingo Molnar

hw breakpoints: Fix pid namespace bug

2010-09-15T08:43:59+00:00

Hardware breakpoints can't be registered within pid namespaces
because tsk->pid is passed rather than the pid in the current
namespace.

(See https://bugzilla.kernel.org/show_bug.cgi?id=17281 )

This is a quick fix demonstrating the problem but is not the
best method of solving the problem since passing pids internally
is not the best way to avoid pid namespace bugs. Subsequent patches
will show a better solution.

Much thanks to Frederic Weisbecker  for doing the
bulk of the work finding this bug.

Signed-off-by: Matt Helsley 
Signed-off-by: Peter Zijlstra 
Cc: Robin Green 
Cc: Prasad 
Cc: Arnaldo Carvalho de Melo 
Cc: Steven Rostedt 
Cc: Will Deacon 
Cc: Mahesh Salgaonkar 
LKML-Reference: 
Signed-off-by: Ingo Molnar

perf: Provide a separate task context for swevents

2010-09-09T18:46:34+00:00

Since software events are always schedulable, mixing them up with
hardware events (who are not) can lead to funny scheduling oddities.

Giving them their own context solves this.

Signed-off-by: Peter Zijlstra 
Cc: paulus 
Cc: stephane eranian 
Cc: Robert Richter 
Cc: Frederic Weisbecker 
Cc: Lin Ming 
Cc: Yanmin 
LKML-Reference: 
Signed-off-by: Ingo Molnar

perf: Rework the PMU methods

2010-09-09T18:46:30+00:00

Replace pmu::{enable,disable,start,stop,unthrottle} with
pmu::{add,del,start,stop}, all of which take a flags argument.

The new interface extends the capability to stop a counter while
keeping it scheduled on the PMU. We replace the throttled state with
the generic stopped state.

This also allows us to efficiently stop/start counters over certain
code paths (like IRQ handlers).

It also allows scheduling a counter without it starting, allowing for
a generic frozen state (useful for rotating stopped counters).

The stopped state is implemented in two different ways, depending on
how the architecture implemented the throttled state:

 1) We disable the counter:
    a) the pmu has per-counter enable bits, we flip that
    b) we program a NOP event, preserving the counter state

 2) We store the counter state and ignore all read/overflow events

Signed-off-by: Peter Zijlstra 
Cc: paulus 
Cc: stephane eranian 
Cc: Robert Richter 
Cc: Will Deacon 
Cc: Paul Mundt 
Cc: Frederic Weisbecker 
Cc: Cyrill Gorcunov 
Cc: Lin Ming 
Cc: Yanmin 
Cc: Deng-Cheng Zhu 
Cc: David Miller 
Cc: Michael Cree 
LKML-Reference: 
Signed-off-by: Ingo Molnar

perf: Register PMU implementations

2010-09-09T18:46:28+00:00

Simple registration interface for struct pmu, this provides the
infrastructure for removing all the weak functions.

Signed-off-by: Peter Zijlstra 
Cc: paulus 
Cc: stephane eranian 
Cc: Robert Richter 
Cc: Will Deacon 
Cc: Paul Mundt 
Cc: Frederic Weisbecker 
Cc: Cyrill Gorcunov 
Cc: Lin Ming 
Cc: Yanmin 
Cc: Deng-Cheng Zhu 
Cc: David Miller 
Cc: Michael Cree 
LKML-Reference: 
Signed-off-by: Ingo Molnar

Merge branch 'perf-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

2010-08-06T16:30:52+00:00

* 'perf-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: (162 commits)
  tracing/kprobes: unregister_trace_probe needs to be called under mutex
  perf: expose event__process function
  perf events: Fix mmap offset determination
  perf, powerpc: fsl_emb: Restore setting perf_sample_data.period
  perf, powerpc: Convert the FSL driver to use local64_t
  perf tools: Don't keep unreferenced maps when unmaps are detected
  perf session: Invalidate last_match when removing threads from rb_tree
  perf session: Free the ref_reloc_sym memory at the right place
  x86,mmiotrace: Add support for tracing STOS instruction
  perf, sched migration: Librarize task states and event headers helpers
  perf, sched migration: Librarize the GUI class
  perf, sched migration: Make the GUI class client agnostic
  perf, sched migration: Make it vertically scrollable
  perf, sched migration: Parameterize cpu height and spacing
  perf, sched migration: Fix key bindings
  perf, sched migration: Ignore unhandled task states
  perf, sched migration: Handle ignored migrate out events
  perf: New migration tool overview
  tracing: Drop cpparg() macro
  perf: Use tracepoint_synchronize_unregister() to flush any pending tracepoint call
  ...

Fix up trivial conflicts in Makefile and drivers/cpufreq/cpufreq.c

hw_breakpoints: Fix per task breakpoint tracking

2010-06-24T21:33:40+00:00

Freeing a perf event can happen in several ways. A task
calls perf_event_exit_task() right before exiting. This helper
will detach all the events from the task context and queue their
removal through free_event() if they are child tasks. The task
also loses its context reference there.

Releasing the breakpoint slot from the constraint table is made
from free_event() that calls release_bp_slot(). We count the number
of breakpoints this task is running by looking at the task's
perf_event_ctxp and iterating through its attached events.
But at this time, the reference to this context has been cleaned up
already.

So looking at the event->ctx instead of task->perf_event_ctxp
to count the remaining breakpoints should solve the problem.
At least it would for child breakpoints, but not for parent ones.
If the parent exits before the child, it will remove all its
events from the context but free_event() will be called later,
on fd release time. And checking the number of breakpoints the
task has attached to its context at this time is unreliable as all
events have been removed from the context.

To solve this, we keep track of the list of per task breakpoints.
On top of it, we maintain our array of numbers of breakpoints used
by the tasks. We use the context address as a task id.

So, instead of looking at the number of events attached to a context,
we walk through our list of per task breakpoints and count the number
of breakpoints that use the same ctx than the one to be reserved or
released from the constraint table, and update the count on top of this
result.

In the meantime it solves a bad refcounting, it also solves a warning,
reported by Paul.

Badness at /home/paulus/kernel/perf/kernel/hw_breakpoint.c:114
NIP: c0000000000cb470 LR: c0000000000cb46c CTR: c00000000032d9b8
REGS: c000000118e7b570 TRAP: 0700   Not tainted  (2.6.35-rc3-perf-00008-g76b0f13
)
MSR: 9000000000029032   CR: 44004424  XER: 000fffff
TASK = c0000001187dcad0[3143] 'perf' THREAD: c000000118e78000 CPU: 1
GPR00: c0000000000cb46c c000000118e7b7f0 c0000000009866a0 0000000000000020
GPR04: 0000000000000000 000000000000001d 0000000000000000 0000000000000001
GPR08: c0000000009bed68 c00000000086dff8 c000000000a5bf10 0000000000000001
GPR12: 0000000024004422 c00000000ffff200 0000000000000000 0000000000000000
GPR16: 0000000000000000 0000000000000000 0000000000000018 00000000101150f4
GPR20: 0000000010206b40 0000000000000000 0000000000000000 00000000101150f4
GPR24: c0000001199090c0 0000000000000001 0000000000000000 0000000000000001
GPR28: 0000000000000000 0000000000000000 c0000000008ec290 0000000000000000
NIP [c0000000000cb470] .task_bp_pinned+0x5c/0x12c
LR [c0000000000cb46c] .task_bp_pinned+0x58/0x12c
Call Trace:
[c000000118e7b7f0] [c0000000000cb46c] .task_bp_pinned+0x58/0x12c (unreliable)
[c000000118e7b8a0] [c0000000000cb584] .toggle_bp_task_slot+0x44/0xe4
[c000000118e7b940] [c0000000000cb6c8] .toggle_bp_slot+0xa4/0x164
[c000000118e7b9f0] [c0000000000cbafc] .release_bp_slot+0x44/0x6c
[c000000118e7ba80] [c0000000000c4178] .bp_perf_event_destroy+0x10/0x24
[c000000118e7bb00] [c0000000000c4aec] .free_event+0x180/0x1bc
[c000000118e7bbc0] [c0000000000c54c4] .perf_event_release_kernel+0x14c/0x170

Reported-by: Paul Mackerras 
Signed-off-by: Frederic Weisbecker 
Cc: Ingo Molnar 
Cc: Peter Zijlstra 
Cc: Arnaldo Carvalho de Melo 
Cc: Prasad 
Cc: Mahesh Salgaonkar 
Cc: Will Deacon 
Cc: Jason Wessel

hw_breakpoints: Allow arch-specific cleanup before breakpoint unregistration

2010-06-22T09:40:50+00:00

Certain architectures (such as PowerPC) have a need to clean up data
structures before a breakpoint is unregistered.  This introduces an
arch-specific hook in release_bp_slot() along with a weak definition
in the form of a stub function.

Signed-off-by: K.Prasad 
Acked-by: Frederic Weisbecker 
Signed-off-by: Paul Mackerras