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On 5/18/26 10:38 AM, Aboorva Devarajan wrote: > kexec_prepare_cpus_wait() calls get_cpu() internally to obtain the > current CPU id. kexec_prepare_cpus() calls kexec_prepare_cpus_wait() > twice -- once for KEXEC_STATE_IRQS_OFF and once for > KEXEC_STATE_REAL_MODE -- but only issues a single put_cpu() at the end, > leaving preempt_count elevated by one extra nesting level. > > In practice the imbalance does not trigger a 'scheduling while atomic' > splat because the kexec path is a one-way trip: IRQs are already > disabled, no schedule() occurs after the leak, and > default_machine_kexec() overwrites preempt_count with HARDIRQ_OFFSET > before jumping into kexec_sequence() which never returns. However the > bookkeeping is still wrong. > > Lift the get_cpu()/put_cpu() pair into kexec_prepare_cpus() so it is > called exactly once, and pass the CPU id to kexec_prepare_cpus_wait() > as a parameter. This keeps preempt_count correctly balanced. > > Fixes: 1fc711f7ffb01 ("powerpc/kexec: Fix race in kexec shutdown") > Signed-off-by: Aboorva Devarajan > --- > arch/powerpc/kexec/core_64.c | 15 ++++++++------- > 1 file changed, 8 insertions(+), 7 deletions(-) > > diff --git a/arch/powerpc/kexec/core_64.c b/arch/powerpc/kexec/core_64.c > index 825ab8a88f18e..9d7e5a1e6e5b8 100644 > --- a/arch/powerpc/kexec/core_64.c > +++ b/arch/powerpc/kexec/core_64.c > @@ -164,12 +164,11 @@ static void kexec_smp_down(void *arg) > /* NOTREACHED */ > } > > -static void kexec_prepare_cpus_wait(int wait_state) > +static void kexec_prepare_cpus_wait(int wait_state, int my_cpu) > { > - int my_cpu, i, notified=-1; > + int i, notified = -1; > > hw_breakpoint_disable(); > - my_cpu = get_cpu(); > /* Make sure each CPU has at least made it to the state we need. > * > * FIXME: There is a (slim) chance of a problem if not all of the CPUs > @@ -246,6 +245,8 @@ static void wake_offline_cpus(void) > > static void kexec_prepare_cpus(void) > { > + int my_cpu; > + > wake_offline_cpus(); > smp_call_function(kexec_smp_down, NULL, /* wait */0); > local_irq_disable(); > @@ -254,7 +255,8 @@ static void kexec_prepare_cpus(void) > mb(); /* make sure IRQs are disabled before we say they are */ > get_paca()->kexec_state = KEXEC_STATE_IRQS_OFF; > > - kexec_prepare_cpus_wait(KEXEC_STATE_IRQS_OFF); > + my_cpu = get_cpu(); raw_smp_processor_id() is better here. All it needs is get current cpu? caller does irq_disable above and that renders call for get_cpu un-necessary. > + kexec_prepare_cpus_wait(KEXEC_STATE_IRQS_OFF, my_cpu); > /* we are sure every CPU has IRQs off at this point */ > kexec_all_irq_disabled = 1; > > @@ -262,13 +264,12 @@ static void kexec_prepare_cpus(void) > * Before removing MMU mappings make sure all CPUs have entered real > * mode: > */ > - kexec_prepare_cpus_wait(KEXEC_STATE_REAL_MODE); > + kexec_prepare_cpus_wait(KEXEC_STATE_REAL_MODE, my_cpu); > + put_cpu(); > > /* after we tell the others to go down */ > if (ppc_md.kexec_cpu_down) > ppc_md.kexec_cpu_down(0, 0); > - > - put_cpu(); > } > > #else /* ! SMP */