Makefile: tell gcc optimizer to never introduce new data races

We have been chasing a memory corruption bug, which turned out to be
caused by very old gcc (4.3.4), which happily turned conditional load
into a non-conditional one, and that broke correctness (the condition
was met only if lock was held) and corrupted memory.

This particular problem with that particular code did not happen when
never gccs were used.  I've brought this up with our gcc folks, as I
wanted to make sure that this can't really happen again, and it turns
out it actually can.

Quoting Martin Jambor <mjambor@suse.cz>:
 "More current GCCs are more careful when it comes to replacing a
  conditional load with a non-conditional one, most notably they check
  that a store happens in each iteration of _a_ loop but they assume
  loops are executed.  They also perform a simple check whether the
  store cannot trap which currently passes only for non-const
  variables.  A simple testcase demonstrating it on an x86_64 is for
  example the following:

  $ cat cond_store.c

  int g_1 = 1;

  int g_2[1024] __attribute__((section ("safe_section"), aligned (4096)));

  int c = 4;

  int __attribute__ ((noinline))
  foo (void)
  {
    int l;
    for (l = 0; (l != 4); l++) {
      if (g_1)
        return l;
      for (g_2[0] = 0; (g_2[0] >= 26); ++g_2[0])
        ;
    }
    return 2;
  }

  int main (int argc, char* argv[])
  {
    if (mprotect (g_2, sizeof(g_2), PROT_READ) == -1)
      {
        int e = errno;
        error (e, e, "mprotect error %i", e);
      }
    foo ();
    __builtin_printf("OK\n");
    return 0;
  }
  /* EOF */
  $ ~/gcc/trunk/inst/bin/gcc cond_store.c -O2 --param allow-store-data-races=0
  $ ./a.out
  OK
  $ ~/gcc/trunk/inst/bin/gcc cond_store.c -O2 --param allow-store-data-races=1
  $ ./a.out
  Segmentation fault

  The testcase fails the same at least with 4.9, 4.8 and 4.7.  Therefore
  I would suggest building kernels with this parameter set to zero. I
  also agree with Jikos that the default should be changed for -O2.  I
  have run most of the SPEC 2k6 CPU benchmarks (gamess and dealII
  failed, at -O2, not sure why) compiled with and without this option
  and did not see any real difference between respective run-times"

Hopefully the default will be changed in newer gccs, but let's force it
for kernel builds so that we are on a safe side even when older gcc are
used.

The code in question was out-of-tree printk-in-NMI (yeah, surprise
suprise, once again) patch written by Petr Mladek, let me quote his
comment from our internal bugzilla:

 "I have spent few days investigating inconsistent state of kernel ring buffer.
  It went out that it was caused by speculative store generated by
  gcc-4.3.4.

  The problem is in assembly generated for make_free_space(). The functions is
  called the following way:

  + vprintk_emit();
      + log = MAIN_LOG; // with logbuf_lock
         or
         log = NMI_LOG; // with nmi_logbuf_lock
         cont_add(log, ...);
          + cont_flush(log, ...);
              + log_store(log, ...);
                    + log_make_free_space(log, ...);

  If called with log = NMI_LOG then only nmi_log_* global variables are safe to
  modify but the generated code does store also into (main_)log_* global
  variables:

  <log_make_free_space>:
         55                      push   %rbp
         89 f6                   mov    %esi,%esi

         48 8b 05 03 99 51 01    mov    0x1519903(%rip),%rax       # ffffffff82620868 <nmi_log_next_id>
         44 8b 1d ec 98 51 01    mov    0x15198ec(%rip),%r11d      # ffffffff82620858 <log_next_idx>
         8b 35 36 60 14 01       mov    0x1146036(%rip),%esi       # ffffffff8224cfa8 <log_buf_len>
         44 8b 35 33 60 14 01    mov    0x1146033(%rip),%r14d      # ffffffff8224cfac <nmi_log_buf_len>
         4c 8b 2d d0 98 51 01    mov    0x15198d0(%rip),%r13       # ffffffff82620850 <log_next_seq>
         4c 8b 25 11 61 14 01    mov    0x1146111(%rip),%r12       # ffffffff8224d098 <log_buf>
         49 89 c2                mov    %rax,%r10
         48 21 c2                and    %rax,%rdx
         48 8b 1d 0c 99 55 01    mov    0x155990c(%rip),%rbx       # ffffffff826608a0 <nmi_log_buf>
         49 c1 ea 20             shr    $0x20,%r10
         48 89 55 d0             mov    %rdx,-0x30(%rbp)
         44 29 de                sub    %r11d,%esi
         45 29 d6                sub    %r10d,%r14d
         4c 8b 0d 97 98 51 01    mov    0x1519897(%rip),%r9	# ffffffff82620840 <log_first_seq>
         eb 7e                   jmp    ffffffff81107029	<log_make_free_space+0xe9>
  [...]
         85 ff                   test   %edi,%edi                  # edi = 1 for NMI_LOG
         4c 89 e8                mov    %r13,%rax
         4c 89 ca                mov    %r9,%rdx
         74 0a                   je     ffffffff8110703d	<log_make_free_space+0xfd>
         8b 15 27 98 51 01       mov    0x1519827(%rip),%edx       # ffffffff82620860 <nmi_log_first_id>
         48 8b 45 d0             mov    -0x30(%rbp),%rax
         48 39 c2                cmp    %rax,%rdx                  # end of loop
         0f 84 da 00 00 00       je     ffffffff81107120 <log_make_free_space+0x1e0>
  [...]
         85 ff                   test   %edi,%edi                  # edi = 1 for NMI_LOG
         4c 89 0d 17 97 51 01    mov    %r9,0x1519717(%rip)        # ffffffff82620840 <log_first_seq>
                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^
                                 KABOOOM
         74 35                   je     ffffffff81107160		 <log_make_free_space+0x220>

  It stores log_first_seq when edi == NMI_LOG. This instructions are used also
  when edi == MAIN_LOG but the store is done speculatively before the condition
  is decided.  It is unsafe because we do not have "logbuf_lock" in NMI context
  and some other process migh modify "log_first_seq" in parallel"

I believe that the best course of action is both

 - building kernel (and anything multi-threaded, I guess) with that
   optimization turned off
 - persuade gcc folks to change the default for future releases

Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Cc: Martin Jambor <mjambor@suse.cz>
Cc: Petr Mladek <pmladek@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Marek Polacek <polacek@redhat.com>
Cc: Jakub Jelinek <jakub@redhat.com>
Cc: Steven Noonan <steven@uplinklabs.net>
Cc: Richard Biener <richard.guenther@gmail.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Makefile: enable -Werror=implicit-int and -Werror=strict-prototypes by default

The common error found in forward-ported/backported patches is missing
headers.  One recent example (files and function names are mangled):

    void foo(){}
    EXPORT_SYMBOL(foo);

gave only warning

    foo.c:12345678:5: warning: function declaration isn't a prototype [-Wstrict-prototypes]
    void foo(){}
         ^

    foo.c:12345679:5: warning: data definition has no type or storage class [enabled by default]
    EXPORT_SYMBOL(foo);
    foo.c:12345679:5: warning: type defaults to 'int' in declaration of 'EXORT_SYMBOL' [-Werror=implicit-int]

Now it's a fatal error. Tested on x86_64 allyesconfig.

[akpm@linux-foundation.org: fix typos in comments]
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
cpufreq: interactive: Add max_freq_hysteresis feature

Previously known as sampling down factor, max_freq_hysteresis
extends the period that interactive governor will stay at policy->max.
This feature is to accomodate short idle periods in an otherwise very
intensive workload.

When the feature is enabled, it ensures that once a CPU goes to max
frequency, it doesn't reduce the frequency for max_freq_hysteresis
microseconds from the time it first goes to idle.

Change-Id: Ia54985cb554f63f8c22d0b554a0a0f2ed2be038f
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>
cpufreq: interactive: Exercise hispeed settings at a policy level

If a heavy task migrates between otherwise idle CPUs in a policy during
every sample window, the above hispeed delay window for the CPUs would get
restarted for every sample window. Due to the continuous restart of above
hispeed delay window, none of the CPUs would ever pick a target frequency
higher than hispeed frequency. This causes the policy's frequency to be
stuck at hispeed freq even if the load justifies a higher frequency.

To fix this, the above high speed delay window is restarted only when the
policy frequency changes. This ensures that tasks migrating between CPUs in
a policy are handled correctly.

Also, the hispeed load/frequency heuristic is only necessary when the
information is insufficient to determine if the load on the CPU needs at
least hispeed frequency. When the policy frequency is already at or above
hispeed frequency, if the CPU load% based on policy frequency is not above
hispeed load, then the information is clearly sufficient to determine that
the load on the CPU does not need hispeed frequency.

Therefore, compute CPU load% (which is used only to compare against hispeed
load) based on policy frequency instead of CPU target frequency.

Change-Id: I1749d663949e34753ecb5c426a16563796f8b0b2
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
cpufreq: hellsactive: Add max_freq_hysteresis feature

Previously known as sampling down factor, max_freq_hysteresis
extends the period that interactive governor will stay at policy->max.
This feature is to accomodate short idle periods in an otherwise very
intensive workload.

When the feature is enabled, it ensures that once a CPU goes to max
frequency, it doesn't reduce the frequency for max_freq_hysteresis
microseconds from the time it first goes to idle.

Change-Id: Ia54985cb554f63f8c22d0b554a0a0f2ed2be038f
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>
cpufreq: hellsactive: Exercise hispeed settings at a policy level

If a heavy task migrates between otherwise idle CPUs in a policy during
every sample window, the above hispeed delay window for the CPUs would get
restarted for every sample window. Due to the continuous restart of above
hispeed delay window, none of the CPUs would ever pick a target frequency
higher than hispeed frequency. This causes the policy's frequency to be
stuck at hispeed freq even if the load justifies a higher frequency.

To fix this, the above high speed delay window is restarted only when the
policy frequency changes. This ensures that tasks migrating between CPUs in
a policy are handled correctly.

Also, the hispeed load/frequency heuristic is only necessary when the
information is insufficient to determine if the load on the CPU needs at
least hispeed frequency. When the policy frequency is already at or above
hispeed frequency, if the CPU load% based on policy frequency is not above
hispeed load, then the information is clearly sufficient to determine that
the load on the CPU does not need hispeed frequency.

Therefore, compute CPU load% (which is used only to compare against hispeed
load) based on policy frequency instead of CPU target frequency.

Change-Id: I1749d663949e34753ecb5c426a16563796f8b0b2
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
msm_mpdecision: Remove boost framework
cpufreq: Add cpu-boost driver

When certain bursty and important events take place, it might take a while
for the current cpufreq governor to notice the new load and react to it.
That would result in poor user experience. To alleviate this, the cpu-boost
driver boosts the frequency of a CPU for a short duration to maintain good
user experience while the governor catches up.

Specifically, this commit deals with ensuring that when "important" tasks
migrate from a fast CPU to a slow CPU, the frequency of the slow CPU is
boosted to be at least as high as the fast CPU for a short duration.

Since this driver enforces the boost by hooking into standard cpufreq
ADJUST notifiers, it has several advantages:
- More portable across kernel versions where the cpufreq internals might
  have been rewritten.
- Governor agnostic and hence works with multiple governors like
  conservative, ondemand, interactive, etc.
- Does not affect the sampling period/logic of existing governors.
- Can have the boost period adjusted independent of governor sampling
  period.

Change-Id: Ibd814a20043d0aba64ee7637a4a79b9ffa1b0991
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
cpufreq: Add a sync limit to cpu-boost

Perform frequency synchronization only when source CPU's frequency
is less than sync_threshold, else sync to the sync_threshold.

Change-Id: I544c414568d4e015b80ce5891dd215275bac95da
Signed-off-by: Rohit Gupta <rohgup@codeaurora.org>
cpufreq: Add Input Boost feature to the cpu-boost driver

On incoming input events boost the frequency of all online cpus
for at least input_boost_ms ms. This is accomplished by changing
the policy->min of all the online cpus to input_boost_freq.

Change-Id: Idb0ab75d68ae4ceff259cbbaaec1a9bb3bc871d3
Signed-off-by: Rohit Gupta <rohgup@codeaurora.org>
cpufreq: Disable cpu-boost by default

Disable cpu-boost by default, so that it can be turned ON only by
setting the module parameter boost_ms through command prompt when
required.

Change-Id: Ia9bc280892f65ed1d2e8051d1951e51922ad13db
Signed-off-by: Rohit Gupta <rohgup@codeaurora.org>
cpufreq: cpu-boost: Fix queue_delayed_work_on() race with hotplug

Calling queue_delayed_work_on() on a CPU that's in the process of getting
hotplugged out can result in that CPU infinitely looping in
msm_pm_wait_cpu_shutdown(). If queue_delayed_work_on() is called after the
CPU is hotplugged out, it could wake up the CPU without going through the
hotplug path and cause instability. To avoid this, make sure the CPU is and
stays online while queuing a work on it.

Change-Id: I1b4aae3db803e476b1a7676d08f495c1f38bb154
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
cpufreq: cpu-boost: Fix deadlock in wake_up of sync threads

If wake_up() is called on the current task on a CPU, the call will wait
until the current task is switched out before it wakes it up again and
returns.

The sync notifier for a CPU always runs on that CPU.

These two together can result in a deadlock if the sync notifier on CPU A
tries to wake up the sync thread of CPU A as it goes to sleep (is the
current task). A previous commit fixed this by adding a check to the sync
notifier to not wake up the sync thread of CPU A if it's the current task.

But this is still not sufficient to prevent deadlocks.

Sync thread of CPU A could be the current task on CPU B and sync thread of
CPU B could be the current task on CPU A.  At this point, if sync notifier
of CPU A and B try to wake up the sync threads of CPU A and B, it will
result in CPU A waiting for the current task in CPU B to get switched out
and CPU B waiting for the current task in CPU A to get switched out.  This
will result in a deadlock.

Prevent this scenario from happening by pinning the sync threads of each
CPU to run on that CPU. By doing this, we guarantee that sync notifiers
will only try to wake up sync threads running on that CPU. The fix added by
"cpufreq: cpu-boost: Resolve deadlock when waking up sync thread" ensures a
deadlock doesn't happen when a sync notifier tries to wake up a sync thread
running on that CPU.

Change-Id: I864e545529722a23886dd5a82f66089155d2d193
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
cpufreq: cpu-boost: Don't register for cpufreq notifiers too early

The cpufreq notifiers should be registered only after all the data
structures used in the notifier callbacks have been initialized. So, move
the cpufreq notifier registration to a later point in the init function.

Change-Id: I043ab5bc0ebb98164c40549fe151a8d801c8c186
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
cpufreq: cpu-boost: Resolve deadlock when waking up sync thread

CPU boost driver receives notification from scheduler when threads
migrate towards a cpu and in turn wakes up a sync thread associated
with that cpu to handle any required frequency transitions. The wakeup
call however can lead to a deadlock inside scheduler under some
circumstance. The deadlock is seen when sync thread is the only thread
running on a cpu and goes to sleep (say by calling wait_event() ->
schedule()). Midway through this sleep (schedule()) call, while cpu is
still running in context of sync thread, scheduler attempts a load
balance (realizing that cpu is about to become idle) which can result
in tasks being migrated towards the cpu going idle. This will cause
migration notification to be issued and in turn a wakeup on sync
thread. The wakeup call however gets stuck in below while() loop
inside scheduler:

try_to_wake_up(struct task_struct *p, ...)
{

        /*
         * If the owning (remote) cpu is still in the middle of
	 * schedule() with this task as prev, wait until its done
	 * referencing the task.
         */
	while (p->on_cpu)
		cpu_relax();

}

A possible fix could be to teach try_to_wake_up() about this
special case. Another fix, implemented in this patch and that helps
minimize scheduler changes, is to have cpu boost driver not issue a
wakeup under this special circumstance, which was found to occur very
infrequently.

Change-Id: I92bc68a22d51595a208673fe2a1eedfa97004f9e
Signed-off-by: Srivatsa Vaddagiri <vatsa@codeaurora.org>
cpufreq: cpu-boost: Re-issue boosts above minimum frequency

Frequency boosts where the source CPU frequency is greater than CPU's
minimum frequency should always go through regardless of the destination
CPU's current frequency. This fixes a performance issue where the governor
lowers the CPU frequency shortly after a thread is migrated to it because
the boost wasn't re-issued.

Change-Id: I449545a688d84b0a6e834f5a51dcb499caa84d29
Signed-off-by: Patrick Cain <pcain@codeaurora.org>
cpufreq: Sync on thread migration optimizations

When threads migrate between CPUs the destination CPU will temporarily
have a boosted frequency and the source CPU will have a residual higher
frequency even though the load could have just been reduced. To avoid
leaving CPUs at a high frequencies notify the source CPU after a thread
migration and make the interactive governor's timer reschedule
conditionally.

Change-Id: Id55055f2a116ca7ffd2a34dc3d0ec519c888a111
Signed-off-by: Patrick Cain <pcain@codeaurora.org>
cpufreq: cpu-boost: Use interruptible wait to not affect load average

Using the function wait_event in cpu_boost puts the
process enter to 'D' state which contribute to the
high load average. This change will put the process
boost_sync in the 'S' state (interruptible sleep)

Change-Id: Ie121adbe1fac1d2862ac5342bb97c7c926f7d7a8
CRs-Fixed: 655484
Signed-off-by: Swetha Chikkaboraiah <schikk@codeaurora.org>
Signed-off-by: Raghavendra Ambadas <rambad@codeaurora.org>
cpufreq: interactive: Make window alignment optional

Make sampling window alignment optional when scheduler inputs
are not enabled.

Change-Id: If69c111a3efe219cdd1e38c1f46f03404789c0bb
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>
hells_defconfig: Refresh