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From f521236471a577e15243b9cc9a7b705a00b68443 Mon Sep 17 00:00:00 2001
From: Anders Roxell <anders.roxell@linaro.org>
Date: Thu, 14 May 2015 17:52:17 +0200
Subject: [PATCH 263/323] arch/arm64: Add lazy preempt support
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.215-rt107.tar.xz
arm64 is missing support for PREEMPT_RT. The main feature which is
lacking is support for lazy preemption. The arch-specific entry code,
thread information structure definitions, and associated data tables
have to be extended to provide this support. Then the Kconfig file has
to be extended to indicate the support is available, and also to
indicate that support for full RT preemption is now available.
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>
---
arch/arm64/Kconfig | 1 +
arch/arm64/include/asm/preempt.h | 25 ++++++++++++++++++++++++-
arch/arm64/include/asm/thread_info.h | 6 +++++-
arch/arm64/kernel/asm-offsets.c | 1 +
arch/arm64/kernel/entry.S | 13 +++++++++++--
arch/arm64/kernel/signal.c | 2 +-
6 files changed, 43 insertions(+), 5 deletions(-)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 13cf137da999a..7681d7b65c7d4 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -173,6 +173,7 @@ config ARM64
select HAVE_PERF_EVENTS
select HAVE_PERF_REGS
select HAVE_PERF_USER_STACK_DUMP
+ select HAVE_PREEMPT_LAZY
select HAVE_REGS_AND_STACK_ACCESS_API
select HAVE_FUNCTION_ARG_ACCESS_API
select HAVE_FUTEX_CMPXCHG if FUTEX
diff --git a/arch/arm64/include/asm/preempt.h b/arch/arm64/include/asm/preempt.h
index f1486b32502c1..7a5770d825b91 100644
--- a/arch/arm64/include/asm/preempt.h
+++ b/arch/arm64/include/asm/preempt.h
@@ -70,13 +70,36 @@ static inline bool __preempt_count_dec_and_test(void)
* interrupt occurring between the non-atomic READ_ONCE/WRITE_ONCE
* pair.
*/
- return !pc || !READ_ONCE(ti->preempt_count);
+ if (!pc || !READ_ONCE(ti->preempt_count))
+ return true;
+#ifdef CONFIG_PREEMPT_LAZY
+ if ((pc & ~PREEMPT_NEED_RESCHED))
+ return false;
+ if (current_thread_info()->preempt_lazy_count)
+ return false;
+ return test_thread_flag(TIF_NEED_RESCHED_LAZY);
+#else
+ return false;
+#endif
}
static inline bool should_resched(int preempt_offset)
{
+#ifdef CONFIG_PREEMPT_LAZY
+ u64 pc = READ_ONCE(current_thread_info()->preempt_count);
+ if (pc == preempt_offset)
+ return true;
+
+ if ((pc & ~PREEMPT_NEED_RESCHED) != preempt_offset)
+ return false;
+
+ if (current_thread_info()->preempt_lazy_count)
+ return false;
+ return test_thread_flag(TIF_NEED_RESCHED_LAZY);
+#else
u64 pc = READ_ONCE(current_thread_info()->preempt_count);
return pc == preempt_offset;
+#endif
}
#ifdef CONFIG_PREEMPTION
diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
index cdcf307764aad..6eb36a2126e84 100644
--- a/arch/arm64/include/asm/thread_info.h
+++ b/arch/arm64/include/asm/thread_info.h
@@ -29,6 +29,7 @@ struct thread_info {
#ifdef CONFIG_ARM64_SW_TTBR0_PAN
u64 ttbr0; /* saved TTBR0_EL1 */
#endif
+ int preempt_lazy_count; /* 0 => preemptable, <0 => bug */
union {
u64 preempt_count; /* 0 => preemptible, <0 => bug */
struct {
@@ -74,6 +75,7 @@ void arch_release_task_struct(struct task_struct *tsk);
#define TIF_SYSCALL_TRACEPOINT 10 /* syscall tracepoint for ftrace */
#define TIF_SECCOMP 11 /* syscall secure computing */
#define TIF_SYSCALL_EMU 12 /* syscall emulation active */
+#define TIF_NEED_RESCHED_LAZY 13
#define TIF_MEMDIE 18 /* is terminating due to OOM killer */
#define TIF_FREEZE 19
#define TIF_RESTORE_SIGMASK 20
@@ -99,13 +101,15 @@ void arch_release_task_struct(struct task_struct *tsk);
#define _TIF_32BIT (1 << TIF_32BIT)
#define _TIF_SVE (1 << TIF_SVE)
#define _TIF_MTE_ASYNC_FAULT (1 << TIF_MTE_ASYNC_FAULT)
+#define _TIF_NEED_RESCHED_LAZY (1 << TIF_NEED_RESCHED_LAZY)
#define _TIF_NOTIFY_SIGNAL (1 << TIF_NOTIFY_SIGNAL)
#define _TIF_WORK_MASK (_TIF_NEED_RESCHED | _TIF_SIGPENDING | \
_TIF_NOTIFY_RESUME | _TIF_FOREIGN_FPSTATE | \
_TIF_UPROBE | _TIF_FSCHECK | _TIF_MTE_ASYNC_FAULT | \
- _TIF_NOTIFY_SIGNAL)
+ _TIF_NEED_RESCHED_LAZY | _TIF_NOTIFY_SIGNAL)
+#define _TIF_NEED_RESCHED_MASK (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY)
#define _TIF_SYSCALL_WORK (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
_TIF_SYSCALL_TRACEPOINT | _TIF_SECCOMP | \
_TIF_SYSCALL_EMU)
diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index 7d32fc959b1a0..b2f29bd2ae871 100644
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -30,6 +30,7 @@ int main(void)
BLANK();
DEFINE(TSK_TI_FLAGS, offsetof(struct task_struct, thread_info.flags));
DEFINE(TSK_TI_PREEMPT, offsetof(struct task_struct, thread_info.preempt_count));
+ DEFINE(TSK_TI_PREEMPT_LAZY, offsetof(struct task_struct, thread_info.preempt_lazy_count));
DEFINE(TSK_TI_ADDR_LIMIT, offsetof(struct task_struct, thread_info.addr_limit));
#ifdef CONFIG_ARM64_SW_TTBR0_PAN
DEFINE(TSK_TI_TTBR0, offsetof(struct task_struct, thread_info.ttbr0));
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 020a455824bed..d9dd46d7aa72d 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -527,9 +527,18 @@ alternative_if ARM64_HAS_IRQ_PRIO_MASKING
mrs x0, daif
orr x24, x24, x0
alternative_else_nop_endif
- cbnz x24, 1f // preempt count != 0 || NMI return path
- bl arm64_preempt_schedule_irq // irq en/disable is done inside
+
+ cbz x24, 1f // (need_resched + count) == 0
+ cbnz w24, 2f // count != 0
+
+ ldr w24, [tsk, #TSK_TI_PREEMPT_LAZY] // get preempt lazy count
+ cbnz w24, 2f // preempt lazy count != 0
+
+ ldr x0, [tsk, #TSK_TI_FLAGS] // get flags
+ tbz x0, #TIF_NEED_RESCHED_LAZY, 2f // needs rescheduling?
1:
+ bl arm64_preempt_schedule_irq // irq en/disable is done inside
+2:
#endif
mov x0, sp
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index b6fbbd527dd79..94eed0dc3afcd 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -921,7 +921,7 @@ asmlinkage void do_notify_resume(struct pt_regs *regs,
/* Check valid user FS if needed */
addr_limit_user_check();
- if (thread_flags & _TIF_NEED_RESCHED) {
+ if (thread_flags & _TIF_NEED_RESCHED_MASK) {
/* Unmask Debug and SError for the next task */
local_daif_restore(DAIF_PROCCTX_NOIRQ);
--
2.44.0
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