These are some minor changes to enable the __noreturn attribute for
arch_cpu_idle_dead(). (If there are no objections, I can merge the
entire set through the tip tree.)
Until recently [1], in Xen, when a previously offlined CPU was brought
back online, it unexpectedly resumed execution where it left off in the
middle of the idle loop by returning from play_dead() and its caller
arch_cpu_idle_dead().
There were some clever hacks to make that work, but the behavior was
surprising as do_idle() doesn't expect an offlined CPU to return from
the dead in the middle of the function.
Now that Xen has been fixed, make sure arch_cpu_idle_dead() never
returns by marking it __noreturn. This causes the compiler to complain
if an arch-specific implementation might return. It also improves code
generation for both caller and callee.
Patches 1-20 update the arch-specific implementations of the function so
they don't actually return (even in error cases), and make that visible
to the compiler. That's typically done by ending the function with a
call to another noreturn function, or with a BUG().
Patch 21 fixes the weak implementation.
Patch 22 actually adds the __noreturn attribute.
[1] 076cbf5d2163 ("x86/xen: don't let xen_pv_play_dead() return")
Josh Poimboeuf (22):
alpha/cpu: Expose arch_cpu_idle_dead()'s prototype declaration
alpha/cpu: Make sure arch_cpu_idle_dead() doesn't return
arm/cpu: Make sure arch_cpu_idle_dead() doesn't return
arm64/cpu: Mark cpu_die() __noreturn
csky/cpu: Make sure arch_cpu_idle_dead() doesn't return
ia64/cpu: Mark play_dead() __noreturn
loongarch/cpu: Make sure play_dead() doesn't return
loongarch/cpu: Mark play_dead() __noreturn
mips/cpu: Expose play_dead()'s prototype definition
mips/cpu: Make sure play_dead() doesn't return
mips/cpu: Mark play_dead() __noreturn
powerpc/cpu: Mark start_secondary_resume() __noreturn
sh/cpu: Make sure play_dead() doesn't return
sh/cpu: Mark play_dead() __noreturn
sh/cpu: Expose arch_cpu_idle_dead()'s prototype definition
sparc/cpu: Mark cpu_play_dead() __noreturn
x86/cpu: Make sure play_dead() doesn't return
x86/cpu: Mark play_dead() __noreturn
xtensa/cpu: Make sure cpu_die() doesn't return
xtensa/cpu: Mark cpu_die() __noreturn
sched/idle: Make sure weak version of arch_cpu_idle_dead() doesn't
return
sched/idle: Mark arch_cpu_idle_dead() __noreturn
arch/alpha/kernel/process.c | 2 ++
arch/arm/kernel/smp.c | 2 ++
arch/arm64/include/asm/smp.h | 2 +-
arch/csky/kernel/smp.c | 2 ++
arch/ia64/kernel/process.c | 4 ++--
arch/loongarch/include/asm/smp.h | 2 +-
arch/loongarch/kernel/smp.c | 2 +-
arch/mips/include/asm/smp.h | 2 +-
arch/mips/kernel/smp-bmips.c | 3 +++
arch/mips/loongson64/smp.c | 1 +
arch/powerpc/include/asm/smp.h | 2 +-
arch/sh/include/asm/smp-ops.h | 5 +++--
arch/sh/kernel/idle.c | 1 +
arch/sparc/include/asm/smp_64.h | 2 +-
arch/x86/include/asm/smp.h | 3 ++-
arch/x86/kernel/process.c | 2 +-
arch/xtensa/include/asm/smp.h | 2 +-
arch/xtensa/kernel/smp.c | 2 ++
include/linux/cpu.h | 2 +-
kernel/sched/idle.c | 2 +-
tools/objtool/check.c | 1 +
21 files changed, 31 insertions(+), 15 deletions(-)
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2.39.0
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