Message ID | 1532038369-5159-1-git-send-email-vnkgutta@codeaurora.org (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
On Thu, Jul 19, 2018 at 03:12:49PM -0700, Venkata Narendra Kumar Gutta wrote: > Based on the 'commit <8b775be35e41b9f> ("ARM: smp: > BUG() if smp_send_reschedule() is called for an offline cpu")' This commit does not appear to exist in mainline. Which tree is it in? > Sending an IPI_RESCHEDULE to an offline CPU is incorrect and potentially > bad for both power and stability. On some sub-architectures such as MSM, > if a power-collapsed CPU is unexpectedly woken up by an IPI, it will be > begin executing without the preparations that would normally happen as > part of CPU_UP_PREPARE. If clocks, voltage regulators, or other hardware > configuration are not performed, the booting CPU may cause general > instability or (at best) poor power performance since the CPU would be > powered up but not utilized. > > One common cause for such issues is misuse of add_timer_on() or APIs > such as queue_work_on() which call it. If proper precautions are not > taken to block hotplug while these APIs are called then a race may > result in IPIs being sent to CPUs that are already offline. > > This same argument could be applied to other IPIs (with the exception > of IPI_WAKEUP), but the others are already restricted to only online > CPUs by existing mechanisms, so an explicit assertion is not useful. > > Signed-off-by: Matt Wagantall <mattw@codeaurora.org> > Signed-off-by: Trilok Soni <tsoni@codeaurora.org> > Signed-off-by: Venkata Narendra Kumar Gutta <vnkgutta@codeaurora.org> > --- > arch/arm64/kernel/smp.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c > index 2faa986..5e39030 100644 > --- a/arch/arm64/kernel/smp.c > +++ b/arch/arm64/kernel/smp.c > @@ -898,6 +898,7 @@ void handle_IPI(int ipinr, struct pt_regs *regs) > > void smp_send_reschedule(int cpu) > { > + BUG_ON(cpu_is_offline(cpu)); > smp_cross_call(cpumask_of(cpu), IPI_RESCHEDULE); > } Is BUG_ON() appropriate? Why not WARN_ON() and return? AFAICT, arm doesn't have this logic today either. Thanks, Mark.
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c index 2faa986..5e39030 100644 --- a/arch/arm64/kernel/smp.c +++ b/arch/arm64/kernel/smp.c @@ -898,6 +898,7 @@ void handle_IPI(int ipinr, struct pt_regs *regs) void smp_send_reschedule(int cpu) { + BUG_ON(cpu_is_offline(cpu)); smp_cross_call(cpumask_of(cpu), IPI_RESCHEDULE); }