Messages in this thread |  | | Subject | Re: [PATCH 1/1] ppc/crash: Skip spinlocks during crash | From | Christophe Leroy <> | Date | Fri, 27 Mar 2020 07:50:20 +0100 |
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Le 26/03/2020 à 23:28, Leonardo Bras a écrit : > 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;
You are adding a test that reads a global var in the middle of a so hot path ? That must kill performance. Can we do different ?
Christophe
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