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powerpc/kexec: fix double get_cpu() imbalance in kexec_prepare_cpus

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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.

kexec_prepare_cpus() calls local_irq_disable()/hard_irq_disable()
before invoking kexec_prepare_cpus_wait(), so the CPU is already pinned
and the get_cpu()/put_cpu() preempt_disable() bracketing is unnecessary.
Only the current CPU id is needed, so replace get_cpu() with
raw_smp_processor_id() and drop the now-unneeded put_cpu().

Fixes: 1fc711f7ff ("powerpc/kexec: Fix race in kexec shutdown")
Signed-off-by: Aboorva Devarajan <aboorvad@linux.ibm.com>
Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20260605082912.305100-4-aboorvad@linux.ibm.com
This commit is contained in:
Aboorva Devarajan 2026-06-05 13:59:12 +05:30 committed by Madhavan Srinivasan
parent 0ecd26e93e
commit 5c86f1c1f9
1 changed files with 1 additions and 3 deletions
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4
arch/powerpc/kexec/core_64.c
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@ -169,7 +169,7 @@ static void kexec_prepare_cpus_wait(int wait_state)
int my_cpu, i, notified=-1;
hw_breakpoint_disable();
my_cpu = get_cpu();
my_cpu = raw_smp_processor_id();
/* 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
@ -267,8 +267,6 @@ static void kexec_prepare_cpus(void)
/* 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 */