2018-08-27 14:32:32 +00:00
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Subject: x86: Support for lazy preemption
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From: Thomas Gleixner <tglx@linutronix.de>
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Date: Thu, 01 Nov 2012 11:03:47 +0100
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2018-08-31 15:16:36 +00:00
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.18/older/patches-4.18.5-rt3.tar.xz
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2018-08-27 14:32:32 +00:00
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Implement the x86 pieces for lazy preempt.
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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---
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arch/x86/Kconfig | 1 +
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arch/x86/entry/common.c | 4 ++--
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arch/x86/entry/entry_32.S | 17 +++++++++++++++++
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arch/x86/entry/entry_64.S | 16 ++++++++++++++++
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arch/x86/include/asm/preempt.h | 31 ++++++++++++++++++++++++++++++-
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arch/x86/include/asm/thread_info.h | 11 +++++++++++
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arch/x86/kernel/asm-offsets.c | 2 ++
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7 files changed, 79 insertions(+), 3 deletions(-)
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--- a/arch/x86/Kconfig
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+++ b/arch/x86/Kconfig
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@@ -178,6 +178,7 @@ config X86
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select HAVE_HARDLOCKUP_DETECTOR_PERF if PERF_EVENTS && HAVE_PERF_EVENTS_NMI
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select HAVE_PERF_REGS
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select HAVE_PERF_USER_STACK_DUMP
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+ select HAVE_PREEMPT_LAZY
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select HAVE_RCU_TABLE_FREE
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2018-09-06 14:27:51 +00:00
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select HAVE_RCU_TABLE_INVALIDATE if HAVE_RCU_TABLE_FREE
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2018-08-27 14:32:32 +00:00
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select HAVE_REGS_AND_STACK_ACCESS_API
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--- a/arch/x86/entry/common.c
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+++ b/arch/x86/entry/common.c
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@@ -133,7 +133,7 @@ static long syscall_trace_enter(struct p
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#define EXIT_TO_USERMODE_LOOP_FLAGS \
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(_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
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- _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY | _TIF_PATCH_PENDING)
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+ _TIF_NEED_RESCHED_MASK | _TIF_USER_RETURN_NOTIFY | _TIF_PATCH_PENDING)
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static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
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{
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@@ -148,7 +148,7 @@ static void exit_to_usermode_loop(struct
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/* We have work to do. */
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local_irq_enable();
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- if (cached_flags & _TIF_NEED_RESCHED)
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+ if (cached_flags & _TIF_NEED_RESCHED_MASK)
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schedule();
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#ifdef ARCH_RT_DELAYS_SIGNAL_SEND
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--- a/arch/x86/entry/entry_32.S
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+++ b/arch/x86/entry/entry_32.S
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@@ -350,8 +350,25 @@ END(ret_from_exception)
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ENTRY(resume_kernel)
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DISABLE_INTERRUPTS(CLBR_ANY)
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.Lneed_resched:
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+ # preempt count == 0 + NEED_RS set?
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cmpl $0, PER_CPU_VAR(__preempt_count)
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+#ifndef CONFIG_PREEMPT_LAZY
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jnz restore_all
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+#else
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+ jz test_int_off
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+
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+ # atleast preempt count == 0 ?
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+ cmpl $_PREEMPT_ENABLED,PER_CPU_VAR(__preempt_count)
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+ jne restore_all
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+
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+ movl PER_CPU_VAR(current_task), %ebp
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+ cmpl $0,TASK_TI_preempt_lazy_count(%ebp) # non-zero preempt_lazy_count ?
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+ jnz restore_all
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+
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+ testl $_TIF_NEED_RESCHED_LAZY, TASK_TI_flags(%ebp)
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+ jz restore_all
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+test_int_off:
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+#endif
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testl $X86_EFLAGS_IF, PT_EFLAGS(%esp) # interrupts off (exception path) ?
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jz restore_all
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call preempt_schedule_irq
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--- a/arch/x86/entry/entry_64.S
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+++ b/arch/x86/entry/entry_64.S
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2018-09-06 14:27:51 +00:00
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@@ -704,7 +704,23 @@ retint_kernel:
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2018-08-27 14:32:32 +00:00
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bt $9, EFLAGS(%rsp) /* were interrupts off? */
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jnc 1f
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0: cmpl $0, PER_CPU_VAR(__preempt_count)
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+#ifndef CONFIG_PREEMPT_LAZY
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jnz 1f
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+#else
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+ jz do_preempt_schedule_irq
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+
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+ # atleast preempt count == 0 ?
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+ cmpl $_PREEMPT_ENABLED,PER_CPU_VAR(__preempt_count)
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+ jnz 1f
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+
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+ movq PER_CPU_VAR(current_task), %rcx
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+ cmpl $0, TASK_TI_preempt_lazy_count(%rcx)
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+ jnz 1f
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+
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+ bt $TIF_NEED_RESCHED_LAZY,TASK_TI_flags(%rcx)
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+ jnc 1f
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+do_preempt_schedule_irq:
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+#endif
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call preempt_schedule_irq
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jmp 0b
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1:
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--- a/arch/x86/include/asm/preempt.h
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+++ b/arch/x86/include/asm/preempt.h
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@@ -86,17 +86,46 @@ static __always_inline void __preempt_co
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* a decrement which hits zero means we have no preempt_count and should
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* reschedule.
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*/
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-static __always_inline bool __preempt_count_dec_and_test(void)
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+static __always_inline bool ____preempt_count_dec_and_test(void)
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{
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GEN_UNARY_RMWcc("decl", __preempt_count, __percpu_arg(0), e);
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}
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+static __always_inline bool __preempt_count_dec_and_test(void)
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+{
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+ if (____preempt_count_dec_and_test())
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+ return true;
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+#ifdef CONFIG_PREEMPT_LAZY
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+ if (current_thread_info()->preempt_lazy_count)
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+ return false;
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+ return test_thread_flag(TIF_NEED_RESCHED_LAZY);
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+#else
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+ return false;
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+#endif
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+}
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+
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/*
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* Returns true when we need to resched and can (barring IRQ state).
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*/
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static __always_inline bool should_resched(int preempt_offset)
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{
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+#ifdef CONFIG_PREEMPT_LAZY
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+ u32 tmp;
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+
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+ tmp = raw_cpu_read_4(__preempt_count);
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+ if (tmp == preempt_offset)
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+ return true;
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+
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+ /* preempt count == 0 ? */
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+ tmp &= ~PREEMPT_NEED_RESCHED;
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+ if (tmp)
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+ return false;
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+ if (current_thread_info()->preempt_lazy_count)
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+ return false;
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+ return test_thread_flag(TIF_NEED_RESCHED_LAZY);
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+#else
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return unlikely(raw_cpu_read_4(__preempt_count) == preempt_offset);
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+#endif
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}
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#ifdef CONFIG_PREEMPT
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--- a/arch/x86/include/asm/thread_info.h
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+++ b/arch/x86/include/asm/thread_info.h
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@@ -56,17 +56,24 @@ struct task_struct;
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struct thread_info {
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unsigned long flags; /* low level flags */
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u32 status; /* thread synchronous flags */
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+ int preempt_lazy_count; /* 0 => lazy preemptable
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+ <0 => BUG */
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};
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#define INIT_THREAD_INFO(tsk) \
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{ \
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.flags = 0, \
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+ .preempt_lazy_count = 0, \
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}
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#else /* !__ASSEMBLY__ */
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#include <asm/asm-offsets.h>
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+#define GET_THREAD_INFO(reg) \
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+ _ASM_MOV PER_CPU_VAR(cpu_current_top_of_stack),reg ; \
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+ _ASM_SUB $(THREAD_SIZE),reg ;
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+
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#endif
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/*
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@@ -83,6 +90,7 @@ struct thread_info {
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#define TIF_SYSCALL_EMU 6 /* syscall emulation active */
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#define TIF_SYSCALL_AUDIT 7 /* syscall auditing active */
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#define TIF_SECCOMP 8 /* secure computing */
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+#define TIF_NEED_RESCHED_LAZY 9 /* lazy rescheduling necessary */
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#define TIF_USER_RETURN_NOTIFY 11 /* notify kernel of userspace return */
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#define TIF_UPROBE 12 /* breakpointed or singlestepping */
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#define TIF_PATCH_PENDING 13 /* pending live patching update */
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@@ -110,6 +118,7 @@ struct thread_info {
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#define _TIF_SYSCALL_EMU (1 << TIF_SYSCALL_EMU)
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#define _TIF_SYSCALL_AUDIT (1 << TIF_SYSCALL_AUDIT)
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#define _TIF_SECCOMP (1 << TIF_SECCOMP)
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+#define _TIF_NEED_RESCHED_LAZY (1 << TIF_NEED_RESCHED_LAZY)
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#define _TIF_USER_RETURN_NOTIFY (1 << TIF_USER_RETURN_NOTIFY)
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#define _TIF_UPROBE (1 << TIF_UPROBE)
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#define _TIF_PATCH_PENDING (1 << TIF_PATCH_PENDING)
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@@ -151,6 +160,8 @@ struct thread_info {
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#define _TIF_WORK_CTXSW_PREV (_TIF_WORK_CTXSW|_TIF_USER_RETURN_NOTIFY)
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#define _TIF_WORK_CTXSW_NEXT (_TIF_WORK_CTXSW)
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+#define _TIF_NEED_RESCHED_MASK (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY)
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+
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#define STACK_WARN (THREAD_SIZE/8)
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/*
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--- a/arch/x86/kernel/asm-offsets.c
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+++ b/arch/x86/kernel/asm-offsets.c
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@@ -38,6 +38,7 @@ void common(void) {
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BLANK();
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OFFSET(TASK_TI_flags, task_struct, thread_info.flags);
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+ OFFSET(TASK_TI_preempt_lazy_count, task_struct, thread_info.preempt_lazy_count);
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OFFSET(TASK_addr_limit, task_struct, thread.addr_limit);
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BLANK();
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@@ -94,6 +95,7 @@ void common(void) {
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BLANK();
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DEFINE(PTREGS_SIZE, sizeof(struct pt_regs));
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+ DEFINE(_PREEMPT_ENABLED, PREEMPT_ENABLED);
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/* TLB state for the entry code */
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OFFSET(TLB_STATE_user_pcid_flush_mask, tlb_state, user_pcid_flush_mask);
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