Subsystems that want to register CPU hotplug callbacks, as well as perform
initialization for the CPUs that are already online, often do it as shown
below:
get_online_cpus();
for_each_online_cpu(cpu)
init_cpu(cpu);
register_cpu_notifier(&foobar_cpu_notifier);
put_online_cpus();
This is wrong, since it is prone to ABBA deadlocks involving the
cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently
with CPU hotplug operations).
Instead, the correct and race-free way of performing the callback
registration is:
cpu_notifier_register_begin();
for_each_online_cpu(cpu)
init_cpu(cpu);
/* Note the use of the double underscored version of the API */
__register_cpu_notifier(&foobar_cpu_notifier);
cpu_notifier_register_done();
Fix the hw-breakpoint code in arm64 by using this latter form of callback
registration.
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
When a CPU resumes from low-power, it restores HW breakpoint and
watchpoint slots through a CPU PM notifier. Since we want to enable
debugging as early as possible in the resume path, the mdscr content
is restored along the general purpose registers in the cpu_suspend API
and debug exceptions are reenabled when cpu_suspend returns. Since the
CPU PM notifier is run after a CPU has been resumed, we cannot expect
HW breakpoint registers to contain sane values till the notifier is run,
since the HW breakpoints registers content is unknown at reset; this means
that the CPU might run with debug exceptions enabled, mdscr restored but HW
breakpoint registers containing junk values that can trigger spurious
debug exceptions.
This patch fixes current HW breakpoints restore by moving the HW breakpoints
registers restoration to the cpu_suspend API, before the debug exceptions are
enabled. This way, as soon as the cpu_suspend function returns the
kernel can resume debugging with sane values in HW breakpoint registers.
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
When a CPU is shutdown either through CPU idle or suspend to RAM, the
content of HW breakpoint registers must be reset or restored to proper
values when CPU resume from low power states. This patch adds debug register
restore operations to the HW breakpoint control function and implements a
CPU PM notifier that allows to restore the content of HW breakpoint registers
to allow proper suspend/resume operations.
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Most of the code executed to install and uninstall breakpoints is
common and can be factored out in a function that through a runtime
operations type provides the requested implementation.
This patch creates a common function that can be used to install/uninstall
breakpoints and defines the set of operations that can be carried out
through it.
Reviewed-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
This is the ARM part of Christoph's patchset cleaning up the various
uses of __get_cpu_var across the tree.
The idea is to convert __get_cpu_var into either an explicit address
calculation using this_cpu_ptr() or into a use of this_cpu operations
that use the offset. Thereby address calculations are avoided and fewer
registers are used when code is generated.
[will: fixed debug ref counting checks and pcpu array accesses]
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
The __cpuinit type of throwaway sections might have made sense
some time ago when RAM was more constrained, but now the savings
do not offset the cost and complications. For example, the fix in
commit 5e427ec2d0 ("x86: Fix bit corruption at CPU resume time")
is a good example of the nasty type of bugs that can be created
with improper use of the various __init prefixes.
After a discussion on LKML[1] it was decided that cpuinit should go
the way of devinit and be phased out. Once all the users are gone,
we can then finally remove the macros themselves from linux/init.h.
Note that some harmless section mismatch warnings may result, since
notify_cpu_starting() and cpu_up() are arch independent (kernel/cpu.c)
are flagged as __cpuinit -- so if we remove the __cpuinit from
arch specific callers, we will also get section mismatch warnings.
As an intermediate step, we intend to turn the linux/init.h cpuinit
content into no-ops as early as possible, since that will get rid
of these warnings. In any case, they are temporary and harmless.
This removes all the arch/arm64 uses of the __cpuinit macros from
all C files. Currently arm64 does not have any __CPUINIT used in
assembly files.
[1] https://lkml.org/lkml/2013/5/20/589
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Srivatsa S. Bhat