On Fri, 2014-04-11 at 20:57 +0200, Sebastian Andrzej Siewior wrote: > This -RT series didn't crashed within ~4h testing on my ARM and > x86-32. > x86-64 crashed after I started hackbench. I figured out that the crash > does not happen with lazy-preempt disabled. Therefore the last but one > patch in the queue disables lazy preempt on x86-64. With this change the > test box survived ~2h without a crash. I look at this later but it looks > good now.
I think the below fixes it (in a more or less minimalist way), but it's not very pretty. Methinks it would be prettier to either clone the x86 percpu + fold logic, or neutralize that optimization completely when PREEMPT_LAZY is enabled. x86_32 bit is completely untested, x86_64 hasn't exploded.. yet :) --- include/linux/preempt.h | 3 +-- arch/x86/include/asm/preempt.h | 8 ++++++++ arch/x86/kernel/asm-offsets.c | 1 + arch/x86/kernel/entry_32.S | 9 ++++++--- arch/x86/kernel/entry_64.S | 7 +++++-- 5 files changed, 21 insertions(+), 7 deletions(-) --- a/include/linux/preempt.h +++ b/include/linux/preempt.h @@ -126,8 +126,7 @@ do { \ #define preempt_enable_notrace() \ do { \ barrier(); \ - if (unlikely(__preempt_count_dec_and_test() || \ - test_thread_flag(TIF_NEED_RESCHED_LAZY))) \ + if (unlikely(__preempt_count_dec_and_test())) \ __preempt_schedule_context(); \ } while (0) #else --- a/arch/x86/include/asm/preempt.h +++ b/arch/x86/include/asm/preempt.h @@ -94,7 +94,11 @@ static __always_inline bool __preempt_co { if (____preempt_count_dec_and_test()) return true; +#ifdef CONFIG_PREEMPT_LAZY return test_thread_flag(TIF_NEED_RESCHED_LAZY); +#else + return false; +#endif } /* @@ -102,8 +106,12 @@ static __always_inline bool __preempt_co */ static __always_inline bool should_resched(void) { +#ifdef CONFIG_PREEMPT_LAZY return unlikely(!__this_cpu_read_4(__preempt_count) || \ test_thread_flag(TIF_NEED_RESCHED_LAZY)); +#else + return unlikely(!__this_cpu_read_4(__preempt_count)); +#endif } #ifdef CONFIG_PREEMPT --- a/arch/x86/kernel/asm-offsets.c +++ b/arch/x86/kernel/asm-offsets.c @@ -72,4 +72,5 @@ void common(void) { BLANK(); DEFINE(PTREGS_SIZE, sizeof(struct pt_regs)); + DEFINE(_PREEMPT_ENABLED, PREEMPT_ENABLED); } --- a/arch/x86/kernel/entry_32.S +++ b/arch/x86/kernel/entry_32.S @@ -365,19 +365,22 @@ ENTRY(resume_kernel) need_resched: # preempt count == 0 + NEED_RS set? cmpl $0,PER_CPU_VAR(__preempt_count) +#ifndef CONFIG_PREEMPT_LAZY + jnz restore_all +#else jz test_int_off # atleast preempt count == 0 ? - cmpl $_TIF_NEED_RESCHED,PER_CPU_VAR(__preempt_count) + cmpl $_PREEMPT_ENABLED,PER_CPU_VAR(__preempt_count) jne restore_all cmpl $0,TI_preempt_lazy_count(%ebp) # non-zero preempt_lazy_count ? jnz restore_all - testl $_TIF_NEED_RESCHED_LAZY, %ecx + testl $_TIF_NEED_RESCHED_LAZY, TI_flags(%ebp) jz restore_all - test_int_off: +#endif testl $X86_EFLAGS_IF,PT_EFLAGS(%esp) # interrupts off (exception path) ? jz restore_all call preempt_schedule_irq --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -1104,10 +1104,13 @@ ENTRY(native_iret) /* rcx: threadinfo. interrupts off. */ ENTRY(retint_kernel) cmpl $0,PER_CPU_VAR(__preempt_count) +#ifndef CONFIG_PREEMPT_LAZY + jnz retint_restore_args +#else jz check_int_off # atleast preempt count == 0 ? - cmpl $_TIF_NEED_RESCHED,PER_CPU_VAR(__preempt_count) + cmpl $_PREEMPT_ENABLED,PER_CPU_VAR(__preempt_count) jnz retint_restore_args cmpl $0, TI_preempt_lazy_count(%rcx) @@ -1115,8 +1118,8 @@ ENTRY(retint_kernel) bt $TIF_NEED_RESCHED_LAZY,TI_flags(%rcx) jnc retint_restore_args - check_int_off: +#endif bt $9,EFLAGS-ARGOFFSET(%rsp) /* interrupts off? */ jnc retint_restore_args call preempt_schedule_irq -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/