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SubjectRe: [PATCH 1/1] ppc/crash: Skip spinlocks during crash
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oops, forgot to EXPORT_SYMBOL. 
arch_spin_lock*() is used on modules.

Sending v2.

On Thu, 2020-03-26 at 19:28 -0300, Leonardo Bras wrote:
> During a crash, there is chance that the cpus that handle the NMI IPI
> are holding a spin_lock. If this spin_lock is needed by crashing_cpu it
> will cause a deadlock. (rtas_lock and printk logbuf_log as of today)
>
> This is a problem if the system has kdump set up, given if it crashes
> for any reason kdump may not be saved for crash analysis.
>
> Skip spinlocks after NMI IPI is sent to all other cpus.
>
> Signed-off-by: Leonardo Bras <leonardo@linux.ibm.com>
> ---
> arch/powerpc/include/asm/spinlock.h | 6 ++++++
> arch/powerpc/kexec/crash.c | 3 +++
> 2 files changed, 9 insertions(+)
>
> diff --git a/arch/powerpc/include/asm/spinlock.h b/arch/powerpc/include/asm/spinlock.h
> index 860228e917dc..a6381d110795 100644
> --- a/arch/powerpc/include/asm/spinlock.h
> +++ b/arch/powerpc/include/asm/spinlock.h
> @@ -111,6 +111,8 @@ static inline void splpar_spin_yield(arch_spinlock_t *lock) {};
> static inline void splpar_rw_yield(arch_rwlock_t *lock) {};
> #endif
>
> +extern bool crash_skip_spinlock __read_mostly;
> +
> static inline bool is_shared_processor(void)
> {
> #ifdef CONFIG_PPC_SPLPAR
> @@ -142,6 +144,8 @@ static inline void arch_spin_lock(arch_spinlock_t *lock)
> if (likely(__arch_spin_trylock(lock) == 0))
> break;
> do {
> + if (unlikely(crash_skip_spinlock))
> + return;
> HMT_low();
> if (is_shared_processor())
> splpar_spin_yield(lock);
> @@ -161,6 +165,8 @@ void arch_spin_lock_flags(arch_spinlock_t *lock, unsigned long flags)
> local_save_flags(flags_dis);
> local_irq_restore(flags);
> do {
> + if (unlikely(crash_skip_spinlock))
> + return;
> HMT_low();
> if (is_shared_processor())
> splpar_spin_yield(lock);
> diff --git a/arch/powerpc/kexec/crash.c b/arch/powerpc/kexec/crash.c
> index d488311efab1..8a522380027d 100644
> --- a/arch/powerpc/kexec/crash.c
> +++ b/arch/powerpc/kexec/crash.c
> @@ -66,6 +66,8 @@ static int handle_fault(struct pt_regs *regs)
>
> #ifdef CONFIG_SMP
>
> +bool crash_skip_spinlock;
> +
> static atomic_t cpus_in_crash;
> void crash_ipi_callback(struct pt_regs *regs)
> {
> @@ -129,6 +131,7 @@ static void crash_kexec_prepare_cpus(int cpu)
> /* Would it be better to replace the trap vector here? */
>
> if (atomic_read(&cpus_in_crash) >= ncpus) {
> + crash_skip_spinlock = true;
> printk(KERN_EMERG "IPI complete\n");
> return;
> }
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