linux-toradex.git/arch/arm/kernel/smp.c, branch v4.9.76

nmi_backtrace: do a local dump_stack() instead of a self-NMI

2016-10-08T01:46:30+00:00

Currently on arm there is code that checks whether it should call
dump_stack() explicitly, to avoid trying to raise an NMI when the
current context is not preemptible by the backtrace IPI.  Similarly, the
forthcoming arch/tile support uses an IPI mechanism that does not
support generating an NMI to self.

Accordingly, move the code that guards this case into the generic
mechanism, and invoke it unconditionally whenever we want a backtrace of
the current cpu.  It seems plausible that in all cases, dump_stack()
will generate better information than generating a stack from the NMI
handler.  The register state will be missing, but that state is likely
not particularly helpful in any case.

Or, if we think it is helpful, we should be capturing and emitting the
current register state in all cases when regs == NULL is passed to
nmi_cpu_backtrace().

Link: http://lkml.kernel.org/r/1472487169-14923-3-git-send-email-cmetcalf@mellanox.com
Signed-off-by: Chris Metcalf 
Tested-by: Daniel Thompson  [arm]
Reviewed-by: Petr Mladek 
Acked-by: Aaron Tomlin 
Cc: "Rafael J. Wysocki" 
Cc: Russell King 
Cc: Thomas Gleixner 
Cc: Ingo Molnar 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

nmi_backtrace: add more trigger_*_cpu_backtrace() methods

2016-10-08T01:46:30+00:00

Patch series "improvements to the nmi_backtrace code" v9.

This patch series modifies the trigger_xxx_backtrace() NMI-based remote
backtracing code to make it more flexible, and makes a few small
improvements along the way.

The motivation comes from the task isolation code, where there are
scenarios where we want to be able to diagnose a case where some cpu is
about to interrupt a task-isolated cpu.  It can be helpful to see both
where the interrupting cpu is, and also an approximation of where the
cpu that is being interrupted is.  The nmi_backtrace framework allows us
to discover the stack of the interrupted cpu.

I've tested that the change works as desired on tile, and build-tested
x86, arm, mips, and sparc64.  For x86 I confirmed that the generic
cpuidle stuff as well as the architecture-specific routines are in the
new cpuidle section.  For arm, mips, and sparc I just build-tested it
and made sure the generic cpuidle routines were in the new cpuidle
section, but I didn't attempt to figure out which the platform-specific
idle routines might be.  That might be more usefully done by someone
with platform experience in follow-up patches.

This patch (of 4):

Currently you can only request a backtrace of either all cpus, or all
cpus but yourself.  It can also be helpful to request a remote backtrace
of a single cpu, and since we want that, the logical extension is to
support a cpumask as the underlying primitive.

This change modifies the existing lib/nmi_backtrace.c code to take a
cpumask as its basic primitive, and modifies the linux/nmi.h code to use
the new "cpumask" method instead.

The existing clients of nmi_backtrace (arm and x86) are converted to
using the new cpumask approach in this change.

The other users of the backtracing API (sparc64 and mips) are converted
to use the cpumask approach rather than the all/allbutself approach.
The mips code ignored the "include_self" boolean but with this change it
will now also dump a local backtrace if requested.

Link: http://lkml.kernel.org/r/1472487169-14923-2-git-send-email-cmetcalf@mellanox.com
Signed-off-by: Chris Metcalf 
Tested-by: Daniel Thompson  [arm]
Reviewed-by: Aaron Tomlin 
Reviewed-by: Petr Mladek 
Cc: "Rafael J. Wysocki" 
Cc: Russell King 
Cc: Thomas Gleixner 
Cc: Ingo Molnar 
Cc: Ralf Baechle 
Cc: David Miller 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

ARM: 8595/2: apply more __ro_after_init

2016-08-12T15:47:06+00:00

Guided by grsecurity's analogous __read_only markings in arch/arm,
this applies several uses of __ro_after_init to structures that are
only updated during __init.

Signed-off-by: Kees Cook 
Signed-off-by: Russell King

Merge tag 'fixes-rcu-fiq-signed' of git://git.kernel.org/pub/scm/linux/kernel/git/tmlind/linux-omap into fixes

2016-06-19T05:21:52+00:00

Fixes for omaps for v4.7-rc cycle:

- Two boot warning fixes from the RCU tree that should have gotten
  merged several weeks ago already but did not because of issues
  with who merges them. Paul has now split the RCU warning fixes into
  sets for various maintainers.

- Fix ams-delta FIQ regression caused by omap1 sparse IRQ changes

- Fix PM for omap3 boards using timer12 and gptimer, like the
  original beagleboard

- Fix hangs on am437x-sk-evm by lowering the I2C bus speed

* tag 'fixes-rcu-fiq-signed' of git://git.kernel.org/pub/scm/linux/kernel/git/tmlind/linux-omap:
  ARM: dts: am437x-sk-evm: Reduce i2c0 bus speed for tps65218
  ARM: OMAP2+: timer: add probe for clocksources
  ARM: OMAP1: fix ams-delta FIQ handler to work with sparse IRQ
  arm: Use _rcuidle for smp_cross_call() tracepoints
  arm: Use _rcuidle tracepoint to allow use from idle

Signed-off-by: Olof Johansson

arm: Use _rcuidle for smp_cross_call() tracepoints

2016-06-14T23:29:31+00:00

Further testing with false negatives suppressed by commit 293e2421fe25
("rcu: Remove superfluous versions of rcu_read_lock_sched_held()")
identified another unprotected use of RCU from the idle loop.  Because RCU
actively ignores idle-loop code (for energy-efficiency reasons, among
other things), using RCU from the idle loop can result in too-short
grace periods, in turn resulting in arbitrary misbehavior.

The resulting lockdep-RCU splat is as follows:

------------------------------------------------------------------------

===============================
[ INFO: suspicious RCU usage. ]
4.6.0-rc5-next-20160426+ #1112 Not tainted
-------------------------------
include/trace/events/ipi.h:35 suspicious rcu_dereference_check() usage!

other info that might help us debug this:

RCU used illegally from idle CPU!
rcu_scheduler_active = 1, debug_locks = 0
RCU used illegally from extended quiescent state!
no locks held by swapper/0/0.

stack backtrace:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.6.0-rc5-next-20160426+ #1112
Hardware name: Generic OMAP4 (Flattened Device Tree)
[] (unwind_backtrace) from [] (show_stack+0x10/0x14)
[] (show_stack) from [] (dump_stack+0xb0/0xe4)
[] (dump_stack) from [] (smp_cross_call+0xbc/0x188)
[] (smp_cross_call) from [] (generic_exec_single+0x9c/0x15c)
[] (generic_exec_single) from [] (smp_call_function_single_async+0 x38/0x9c)
[] (smp_call_function_single_async) from [] (cpuidle_coupled_poke_others+0x8c/0xa8)
[] (cpuidle_coupled_poke_others) from [] (cpuidle_enter_state_coupled+0x26c/0x390)
[] (cpuidle_enter_state_coupled) from [] (cpu_startup_entry+0x198/0x3a0)
[] (cpu_startup_entry) from [] (start_kernel+0x354/0x3c8)
[] (start_kernel) from [<8000807c>] (0x8000807c)

------------------------------------------------------------------------

Reported-by: Tony Lindgren 
Signed-off-by: Paul E. McKenney 
Tested-by: Tony Lindgren 
Tested-by: Guenter Roeck 
Cc: Russell King 
Cc: Steven Rostedt 
Cc: 
Cc:

printk/nmi: generic solution for safe printk in NMI

2016-05-21T00:58:30+00:00

printk() takes some locks and could not be used a safe way in NMI
context.

The chance of a deadlock is real especially when printing stacks from
all CPUs.  This particular problem has been addressed on x86 by the
commit a9edc8809328 ("x86/nmi: Perform a safe NMI stack trace on all
CPUs").

The patchset brings two big advantages.  First, it makes the NMI
backtraces safe on all architectures for free.  Second, it makes all NMI
messages almost safe on all architectures (the temporary buffer is
limited.  We still should keep the number of messages in NMI context at
minimum).

Note that there already are several messages printed in NMI context:
WARN_ON(in_nmi()), BUG_ON(in_nmi()), anything being printed out from MCE
handlers.  These are not easy to avoid.

This patch reuses most of the code and makes it generic.  It is useful
for all messages and architectures that support NMI.

The alternative printk_func is set when entering and is reseted when
leaving NMI context.  It queues IRQ work to copy the messages into the
main ring buffer in a safe context.

__printk_nmi_flush() copies all available messages and reset the buffer.
Then we could use a simple cmpxchg operations to get synchronized with
writers.  There is also used a spinlock to get synchronized with other
flushers.

We do not longer use seq_buf because it depends on external lock.  It
would be hard to make all supported operations safe for a lockless use.
It would be confusing and error prone to make only some operations safe.

The code is put into separate printk/nmi.c as suggested by Steven
Rostedt.  It needs a per-CPU buffer and is compiled only on
architectures that call nmi_enter().  This is achieved by the new
HAVE_NMI Kconfig flag.

The are MN10300 and Xtensa architectures.  We need to clean up NMI
handling there first.  Let's do it separately.

The patch is heavily based on the draft from Peter Zijlstra, see

  https://lkml.org/lkml/2015/6/10/327

[arnd@arndb.de: printk-nmi: use %zu format string for size_t]
[akpm@linux-foundation.org: min_t->min - all types are size_t here]
Signed-off-by: Petr Mladek 
Suggested-by: Peter Zijlstra 
Suggested-by: Steven Rostedt 
Cc: Jan Kara 
Acked-by: Russell King 	[arm part]
Cc: Daniel Thompson 
Cc: Jiri Kosina 
Cc: Ingo Molnar 
Cc: Thomas Gleixner 
Cc: Ralf Baechle 
Cc: Benjamin Herrenschmidt 
Cc: Martin Schwidefsky 
Cc: David Miller 
Cc: Daniel Thompson 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

arch/hotplug: Call into idle with a proper state

2016-03-01T19:36:57+00:00

Let the non boot cpus call into idle with the corresponding hotplug state, so
the hotplug core can handle the further bringup. That's a first step to
convert the boot side of the hotplugged cpus to do all the synchronization
with the other side through the state machine. For now it'll only start the
hotplug thread and kick the full bringup of the cpu.

Signed-off-by: Thomas Gleixner 
Cc: linux-arch@vger.kernel.org
Cc: Rik van Riel 
Cc: Rafael Wysocki 
Cc: "Srivatsa S. Bhat" 
Cc: Peter Zijlstra 
Cc: Arjan van de Ven 
Cc: Sebastian Siewior 
Cc: Rusty Russell 
Cc: Steven Rostedt 
Cc: Oleg Nesterov 
Cc: Tejun Heo 
Cc: Andrew Morton 
Cc: Paul McKenney 
Cc: Linus Torvalds 
Cc: Paul Turner 
Link: http://lkml.kernel.org/r/20160226182341.614102639@linutronix.de
Signed-off-by: Thomas Gleixner

ARM: 8488/1: Make IPI_CPU_BACKTRACE a "non-secure" SGI

2015-12-22T12:09:44+00:00

Having IPI_CPU_BACKTRACE as SGI15 may not work if the kernel is
running in non-secure mode and that the secure firmware has
decided to follow ARM's recommendations that SGI8-15 should
be reserved for secure purpose.

Now that we are "only" using SGI0-6, change IPI_CPU_BACKTRACE
to use SGI7, which makes it more likely to work.

Signed-off-by: Marc Zyngier 
Signed-off-by: Russell King

ARM: 8487/1: Remove IPI_CALL_FUNC_SINGLE

2015-12-22T12:09:43+00:00

Since 9a46ad6d6df3 ("smp: make smp_call_function_many() use logic
similar to smp_call_function_single()"), the core IPI handling
has been simplified, and generic_smp_call_function_interrupt is
now the same as generic_smp_call_function_single_interrupt.

This means that one of IPI_CALL_FUNC and IPI_CALL_FUNC_SINGLE has
become redundant. We can then safely drop IPI_CALL_FUNC_SINGLE,
and use only IPI_CALL_FUNC.

This has the advantage of reducing the number of SGI IDs we're using
(a fairly scarse resource).

Tested on a dual A7 board.

Signed-off-by: Marc Zyngier 
Signed-off-by: Russell King

ARM: 8439/1: Fix backtrace generation when IPI is masked

2015-10-03T15:40:51+00:00

Currently on ARM when  is triggered from an interrupt handler
(e.g. a SysRq issued using UART or kbd) the main CPU will wedge for ten
seconds with interrupts masked before issuing a backtrace for every CPU
except itself.

The new backtrace code introduced by commit 96f0e00378d4 ("ARM: add
basic support for on-demand backtrace of other CPUs") does not work
correctly when run from an interrupt handler because IPI_CPU_BACKTRACE
is used to generate the backtrace on all CPUs but cannot preempt the
current calling context.

This can be fixed by detecting that the calling context cannot be
preempted and issuing the backtrace directly in this case. Issuing
directly leaves us without any pt_regs to pass to nmi_cpu_backtrace()
so we also modify the generic code to call dump_stack() when its
argument is NULL.

Acked-by: Hillf Danton 
Acked-by: Thomas Gleixner 
Signed-off-by: Daniel Thompson 
Signed-off-by: Russell King