From: Huacai Chen <chenhuacai@kernel.org>
To: Tiezhu Yang <yangtiezhu@loongson.cn>
Cc: loongarch@lists.linux.dev, bpf@vger.kernel.org,
linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 1/3] LoongArch: Implement CONFIG_THREAD_INFO_IN_TASK
Date: Wed, 3 Jun 2026 22:24:05 +0800 [thread overview]
Message-ID: <CAAhV-H51mJpbYjQJYo_a_8mWuG9CSbvbvQNHrpV1G3jmp0Vkaw@mail.gmail.com> (raw)
In-Reply-To: <0def4127-3850-1114-d576-42748456f400@loongson.cn>
On Wed, Jun 3, 2026 at 10:30 AM Tiezhu Yang <yangtiezhu@loongson.cn> wrote:
>
> On 2026/6/1 下午9:46, Huacai Chen wrote:
> > Hi, Tiezhu,
>
> ...
>
> > First of all, you should update
> > Documentation/features/core/thread-info-in-task/arch-support.txt
> > together.
>
> OK, will do it.
>
> >> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> >> index 3b042dbb2c41..ea29d5d17588 100644
> >> --- a/arch/loongarch/Kconfig
> >> +++ b/arch/loongarch/Kconfig
> >> @@ -210,6 +210,7 @@ config LOONGARCH
> >> select SYSCTL_ARCH_UNALIGN_NO_WARN
> >> select SYSCTL_EXCEPTION_TRACE
> >> select SWIOTLB if 64BIT
> >> + select THREAD_INFO_IN_TASK
> >> select TRACE_IRQFLAGS_SUPPORT
> >> select USE_PERCPU_NUMA_NODE_ID
> >> select USER_STACKTRACE_SUPPORT
>
> ...
>
> >> +#define INIT_THREAD { \
> >> + .reg02 = (unsigned long)&init_task, \
> >> + .reg03 = (unsigned long)&init_stack + sizeof(init_stack), \
> >> }
> > Don't remove the old code, just adding reg02 is enough. Though the
> > result is the same, explicitly initialization can give more
> > information.
>
> After thinking it through, the introduction and initialization of
> thread_struct.reg02 (including the assignment in INIT_THREAD and
> p->thread.reg02 = (unsigned long)p; in copy_thread()) are redundant
> and should be removed. The reasons are as follows:
>
> 1. Direct update in __switch_to: In __switch_to within switch.S, the
> hardware $tp register is updated directly from the next argument
> (via register a1) using "move tp, a1".
>
> 2. No restoration path: The cpu_restore_nonscratch macro does not
> include any restoration logic for reg02. This means no assembly
> or C code ever reads thread_struct.reg02 across the entire context
> switch path, whether standard or non-standard.
>
> 3. Exception/Syscall recovery relies on per-CPU variables: At exception
> and system call entry points (e.g., in stackframe.h and entry.S),
> the recovery of the kernel-space $tp relies entirely on the per-CPU
> variable __entry_task, which is already properly and explicitly
> updated during entry_task_switch() and CPU initialization.
>
> Consequently, reg02 is a classic piece of dead code (write-only, never
> read), and trimming this field would keep the architecture code clean.
>
> Regarding the explicit zero-initialization, it is redundant in modern
> kernel development.
>
> For static structures like init_task, any uninitialized fields are
> automatically zeroed out by the compiler according to the C standard.
> Stripping away dozens of lines of ".field = 0" complies with modern
> Linux kernel code-cleaning standards. It makes the macro much shorter
> and highlights the only field that actually requires a special
> runtime value (the kernel stack top in .reg03).
I know it is the same for compilers, I mean the current way gives more
information for humans.
In addition, without reg02, this piece completely has no relationship
with CONFIG_THREAD_INFO_IN_TASK, so please drop it.
>
> For reference, please see how INIT_THREAD is defined in other major
> architectures, where they only initialize what is strictly necessary:
>
> x86
> #ifdef CONFIG_X86_32
> #define INIT_THREAD { \
> .sp0 = TOP_OF_INIT_STACK, \
> .sysenter_cs = __KERNEL_CS, \
> }
>
> #else
> extern unsigned long __top_init_kernel_stack[];
>
> #define INIT_THREAD { \
> .sp = (unsigned long)&__top_init_kernel_stack, \
> }
>
> #endif /* CONFIG_X86_64 */
>
> arm64:
> #define INIT_THREAD { \
> .fpsimd_cpu = NR_CPUS, \
> }
>
> riscv:
> #define INIT_THREAD { \
> .sp = sizeof(init_stack) + (long)&init_stack, \
> .align_ctl = PR_UNALIGN_NOPRINT, \
> }
>
> Therefore, a cleaner and more accurate approach is to drop
> reg02 entirely and adopt the slimmed-down INIT_THREAD for
> LoongArch.
>
> >> struct task_struct;
> >> diff --git a/arch/loongarch/include/asm/ptrace.h b/arch/loongarch/include/asm/ptrace.h
> >> index e5d21e836d99..37f53629d3c7 100644
> >> --- a/arch/loongarch/include/asm/ptrace.h
> >> +++ b/arch/loongarch/include/asm/ptrace.h
> >> @@ -170,12 +170,6 @@ static inline void die_if_kernel(const char *str, struct pt_regs *regs)
> >> die(str, regs);
> >> }
> >>
> >> -#define current_pt_regs() \
> >> -({ \
> >> - unsigned long sp = (unsigned long)__builtin_frame_address(0); \
> >> - (struct pt_regs *)((sp | (THREAD_SIZE - 1)) + 1) - 1; \
> >> -})
> >> -
> > This is still correct after CONFIG_THREAD_INFO_IN_TASK, so please keep
> > it. Especially CONFIG_THREAD_INFO_IN_TASK increases the cost of
> > exception/syscalls, keeping this can minimize the performance
> > impaction.
>
> Regarding the suggestion to keep the custom current_pt_regs() macro
> under CONFIG_THREAD_INFO_IN_TASK, it must be completely removed.
> Keeping it would be fundamentally incorrect and dangerous for the
> following reasons:
>
> 1. It becomes logically incorrect:
>
> The old macro relies on aligning up the $sp to the top of the stack
> via bitwise operations to locate the exact position of pt_regs.
>
> With CONFIG_THREAD_INFO_IN_TASK enabled, the thread_info is moved
> off the stack, and the strict coupling between the masked SP and
> the absolute position of pt_regs is broken (especially if features
> like VMAP_STACK are enabled in the future, where stacks are no
> longer naturally aligned to THREAD_SIZE).
>
> Keeping this macro will cause current_pt_regs() to return a
> corrupted/incorrect pointer, leading to inevitable kernel panics
> or silent data corruption.
I don't think so. CONFIG_THREAD_INFO_IN_TASK decouples TP
(thread_info) and SP (stack), but doesn't decouple SP and THREAD_SIZE,
even for the VMAP_STACK case. This is from RISC-V:
#ifdef CONFIG_VMAP_STACK
#define THREAD_ALIGN (2 * THREAD_SIZE)
#else
#define THREAD_ALIGN THREAD_SIZE
#endif
Stack is still aligned to THREAD_SIZE.
>
> 2. No real performance benefit:
>
> Once CONFIG_THREAD_INFO_IN_TASK is selected, current is simply
> the hardware $tp register. Fetching pt_regs via task_pt_regs()
> just compiles down to loading the stack pointer from $tp with
> a single memory access, followed by a constant offset adjustment.
>
> This is extremely fast and efficient on LoongArch, and it avoids
> multiple ALU operations (or, add, sub) required by the old
> SP-masking macro.
Do you have performance data for the two cases?
>
> 3. Alignment with other architectures:
>
> Other major architectures (such as x86, arm64, and riscv) all
> completely dropped their custom SP-masking current_pt_regs()
> implementations when moving to THREAD_INFO_IN_TASK, relying
> instead on the standard, safe, and generic task_pt_regs()
> provided by the core kernel wrapper.
>
> Therefore, this custom macro is both broken and insecure under
> the new standard, and it must be removed to ensure kernel
> stability and clean code alignment with upstream.
PowerPC, PA-RISC, ARM32 and UML are the latest archs that support
THREAD_INFO_IN_TASK.
PowerPC in 5.1:
ed1cd6deb013a11959d17a94e35ce159197632da powerpc: Activate
CONFIG_THREAD_INFO_IN_TASK.
PA-RISC in 5.16:
2214c0e77259b420402e279e9ab4277ef320d371 parisc: Move thread_info into
task struct.
ARM32 in 5.16:
18ed1c01a7dd3d7c780b06a49124da237a4c1790 ARM: smp: Enable THREAD_INFO_IN_TASK.
UML in 6.13:
2f681ba4b352cdd5658ed2a96062375a12839755 um: move thread info into task.
None of these commits remove current_pt_regs. Some of them has no
current_pt_regs before THREAD_INFO_IN_TASK, and ARM32 still has its
own implementations in arch/arm/include/asm/ptrace.h now which is
nearly the same as LoongArch.
>
> >> /* Helpers for working with the user stack pointer */
>
> ...
>
> >> diff --git a/arch/loongarch/include/asm/stackframe.h b/arch/loongarch/include/asm/stackframe.h
> >> index ecc8e50fffa8..eeda5dcc982e 100644
> >> --- a/arch/loongarch/include/asm/stackframe.h
> >> +++ b/arch/loongarch/include/asm/stackframe.h
> >> @@ -191,8 +191,13 @@
> >> andi t0, t0, 0x3 /* extract pplv bit */
> >> beqz t0, 9f
> >>
> >> - LONG_LI tp, ~_THREAD_MASK
> >> - and tp, tp, sp
> >> + la_abs t1, __entry_task
> >> +#ifdef CONFIG_SMP
> >> + csrrd t0, PERCPU_BASE_KS
> >> + LONG_ADD t1, t1, t0
> >> +#endif
> >> + LONG_L tp, t1, 0
> >> +
> >> cfi_st u0, PT_R21, \docfi
> >> csrrd u0, PERCPU_BASE_KS
> > Move these lines near to "cfi_st fp, PT_R22, \docfi", then the above
> > "csrrd t0, PERCPU_BASE_KS" can be removed.
>
> Regarding the suggestion for stackframe.h:
>
> Looking at the original macro context, this is an excellent and
> completely feasible assembly optimization.
>
> By moving the __entry_task restoration right after the preservation
> of u0, we can advance the "csrrd u0, PERCPU_BASE_KS" instruction and
> reuse the loaded u0 register directly for the LONG_ADD on SMP platforms.
> This completely eliminates the need for a duplicate csrrd instruction
> inside the #ifdef CONFIG_SMP block.
>
> The optimized code block would look like this:
>
> beqz t0, 9f
>
> cfi_st u0, PT_R21, \docfi
> csrrd u0, PERCPU_BASE_KS
>
> la_abs t1, __entry_task
> #ifdef CONFIG_SMP
> LONG_ADD t1, t1, u0
> #endif
> LONG_L tp, t1, 0
>
> 9:
>
> Thank you for catching this! I will gladly incorporate this assembly
> optimization into the next version.
>
> >> diff --git a/arch/loongarch/include/asm/switch_to.h b/arch/loongarch/include/asm/switch_to.h
> >> index 5b225aff3ba2..9932429cfe17 100644
> >> --- a/arch/loongarch/include/asm/switch_to.h
> >> +++ b/arch/loongarch/include/asm/switch_to.h
> >> @@ -5,17 +5,25 @@
> >> #ifndef _ASM_SWITCH_TO_H
> >> #define _ASM_SWITCH_TO_H
> >>
> >> +#include <linux/percpu.h>
> >> +
> >> #include <asm/cpu-features.h>
> >> #include <asm/fpu.h>
> >> #include <asm/lbt.h>
> >>
> >> struct task_struct;
> >>
> >> +DECLARE_PER_CPU(struct task_struct *, __entry_task);
> >> +
> >> +static inline void entry_task_switch(struct task_struct *next)
> >> +{
> >> + __this_cpu_write(__entry_task, next);
> >> +}
> > I love the UML naming, which means rename __entry_task to cpu_tasks
> > and rename entry_task_switch() to set_current(), then move them to
> > current.h.
>
> Regarding the suggestion to rename and move __entry_task and
> entry_task_switch():
>
> Thank you for the suggestion, but after checking the upstream
> kernel implementation, the current naming and placement are
> actually fully aligned with the multi-architecture standards
> established by ARM/ARM64.
>
> A quick grep in the kernel tree reveals that ARM and ARM64
> uses the exact same pattern:
>
> $ grep -rn entry_task arch
> arch/arm/kernel/process.c:40:DEFINE_PER_CPU(struct task_struct *,
> __entry_task);
> arch/arm/include/asm/switch_to.h:31: __this_cpu_write(__entry_task,
> next); \
> arch/arm/include/asm/thread_info.h:40:DECLARE_PER_CPU(struct task_struct
> *, __entry_task);
> arch/arm/include/asm/assembler.h:357: ldr_this_cpu \t1, __entry_task,
> \t1, \t2
> arch/arm64/kernel/process.c:609:DEFINE_PER_CPU(struct task_struct *,
> __entry_task);
> arch/arm64/kernel/process.c:611:static void entry_task_switch(struct
> task_struct *next)
> arch/arm64/kernel/process.c:613: __this_cpu_write(__entry_task, next);
> arch/arm64/kernel/process.c:777: entry_task_switch(next);
> arch/arm64/kernel/entry.S:223: ldr_this_cpu tsk, __entry_task, x20
> arch/arm64/kernel/entry.S:1033: ldr_this_cpu dst=x0, sym=__entry_task,
> tmp=x1
>
> As we can see:
> 1. Moving to current.h is heavily avoided: Both ARM and ARM64 place
> these definitions in process.c or switch_to.h, rather than
> current.h. <asm/current.h> is a highly sensitive, low-level header
> included almost everywhere. Putting per-CPU macros there would pull
> in <linux/percpu.h> and <linux/sched.h>, inevitably triggering
> catastrophic circular header dependency compile errors.
Frankly, I completely don't know what you are doing when I see
"__entry_task" for the first time. Then I see the UML naming and I
know everything immediately.
ARM64 introduces "__entry_task" and in
18ed1c01a7dd3d7c780b06a49124da237a4c1790 ARM32 follows it, and ARM32
only has __entry_task, but no entry_task_switch.
So you can think this naming is a only case rather than a common case.
>
> 2. "__entry_task" and "entry_task_switch" are the precise industry
> standards: Rather than adopting UML's historical naming style,
> following the ARM64 conventions makes the code much more canonical
> and easier for cross-architecture developers to maintain.
> It clearly expresses that this per-CPU pointer is strictly
> dedicated to the exception entry path for task recovery.
As said before, UML is the latest one that introduces
CONFIG_THREAD_INFO_IN_TASK, "cpu_tasks" is not a "historical style",
and x86 uses "current_task" rather than "__entry_task". Both
"cpu_tasks" and "current_task" are better than "__entry_task".
>
> 3. "set_current()" causes mental friction: Across the generic kernel,
> "current" is universally treated as a read-only concept. Introducing
> a set_current() helper might mislead developers into thinking they
> can modify the active task pointer at will, whereas
> "entry_task_switch" explicitly limits its semantics to the context
> switch boundary.
set_current() is a very good friend of get_current(). Though "$tp" is
enough for get_current(), from the x86 implementation we know that it
can also get from the per-cpu array (but suboptimal).
Move set_current() to current.h also don't need to include
<linux/percpu.h> and <linux/sched.h>, it only need to forwarding
declare "task_struct" and include <asm/percpu.h>, which is exactly
done in the x86 implementation.
And you needn't worry about the compiling, I have tested before I comment.
Huacai
>
> Therefore, I prefer to keep the current naming and structure in
> switch_to.h to remain consistent with ARM64 and keep the header
> dependencies perfectly clean.
>
> >> +
> >> /**
> >> * __switch_to - switch execution of a task
> >> * @prev: The task previously executed.
> >> * @next: The task to begin executing.
> >> - * @next_ti: task_thread_info(next).
> >> * @sched_ra: __schedule return address.
> >> * @sched_cfa: __schedule call frame address.
>
> ...
>
> >> struct thread_info {
> >> - struct task_struct *task; /* main task structure */
> >> unsigned long flags; /* low level flags */
> >> - unsigned long tp_value; /* thread pointer */
> > Don't remove tp_value, it has nothing to do with this patch, instead,
> > it is for future LBT tls.
>
> Regarding the suggestion to keep tp_value in thread_info:
>
> You are completely right. I walked into a misunderstanding that
> tp_value was strictly coupled with the kernel-space $tp tracking.
> Since its true purpose is to preserve the user-space TLS value
> for the LBT (Loongson Binary Translation) extension context,
> it should definitely be decoupled from this THREAD_INFO_IN_TASK
> migration.
>
> I will follow the "one patch does one thing" principle and keep
> tp_value untouched in struct thread_info to avoid breaking any
> future or existing LBT TLS logic.
>
> Thank you for clarifying this! I will restore this field in the
> next version.
>
> >> __u32 cpu; /* current CPU */
> >> int preempt_count; /* 0 => preemptible, <0 => BUG */
> >> struct pt_regs *regs;
> >> @@ -37,20 +35,11 @@ struct thread_info {
> >> */
> >> #define INIT_THREAD_INFO(tsk) \
> >> { \
> >> - .task = &tsk, \
> >> - .flags = _TIF_FIXADE, \
> >> + .flags = 0, \
> > Don't change flags.
>
> Regarding the suggestion to keep the flags initialization:
>
> You are completely right. Modifying the default flags (changing
> _TIF_FIXADE to 0) is an unrelated side-effect that goes beyond
> the scope of migrating thread_info.
>
> Changing this could alter the alignment error fixing behavior
> for the initial idle task and cause unexpected regressions.
>
> I will follow your advice, leave the flags logic untouched,
> and only remove the deleted ".task = &tsk" member.
>
> Thank you for your critical review!
>
> >> .cpu = 0, \
> >> .preempt_count = INIT_PREEMPT_COUNT, \
>
> ...
>
> >> @@ -223,6 +226,9 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
> >> if (clone_flags & CLONE_SETTLS)
> >> childregs->regs[2] = tls;
> >>
> >> + /* Set tp to the new task structure for context switching */
> >> + p->thread.reg02 = (unsigned long)p;
> > This should be before "if (unlikely(args->fn))" for kernel thread.
>
> Regarding the feedback on process.c and thread_struct:
>
> Actually, after double-checking the core architecture assembly,
> we don't need to worry about where to place
> "p->thread.reg02 = (unsigned long)p;"
> because this line can be completely deleted, and reg02 shouldn't
> be added to thread_struct at all.
>
> As analyzed previously, during context switch, the hardware $tp
> register is updated directly from the C argument "next" via
> "move tp, a1".
>
> Furthermore, the cpu_restore_nonscratch macro contains absolutely
> no logic to read or restore reg02. This means thread_struct.reg02
> has a write-only path and is never read anywhere (even for new
> processes or kernel threads). To keep the architecture code clean
> and avoid misleading future developers, I will completely drop
> reg02 and its assignment from the next version.
>
> >> +
> >> out:
> >> ptrace_hw_copy_thread(p);
> >> clear_tsk_thread_flag(p, TIF_USEDFPU);
>
> ...
>
> >> +
> >> + entry_task_switch(&init_task);
> > This should be as early as possible, I suggest moving it after unwind_init().
>
> Regarding the suggestion to move entry_task_switch() in setup.c:
>
> You are completely right, and this is a critical catch for early
> boot stability.
>
> Placing entry_task_switch(&init_task) at the very end of
> setup_arch() leaves a massive window during early initialization
> where __entry_task remains NULL.
>
> If any early exception, interrupt, or panic occurs before the end
> of setup_arch(), the exception entry path will load a NULL pointer
> into $tp, triggering an immediate double-fault and completely
> blinding the kernel's ability to print stack traces.
>
> Moving it immediately after unwind_init() ensures that the $tp
> recovery mechanism is armed as early as possible, providing robust
> exception handling support during the rest of the boot sequence.
>
> I will absolutely adopt this suggestion and move it right after
> unwind_init() in the next version. Thank you!
>
> >> }
> >> diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c
> >> index 64a048f1b880..e8b0d2fc2a9a 100644
> >> --- a/arch/loongarch/kernel/smp.c
> >> +++ b/arch/loongarch/kernel/smp.c
>
> ...
>
> >> + entry_task_switch(current);
> > This should be as early as possible, I suggest moving it after cpu_probe().
>
> Regarding the suggestion to move entry_task_switch() in smp.c:
>
> You are completely right, and this is another critical catch for
> early boot stability, this time on the secondary CPU path.
>
> Placing entry_task_switch(current) after complete(&cpu_running)
> leaves a dangerous window during the early C entry of
> start_secondary() where the secondary CPU's __entry_task remains
> uninitialized (NULL). If any early exception or kernel panic
> occurs during the secondary CPU initialization prior to the
> completion signal, the exception entry path will load a NULL
> pointer into $tp, inducing an immediate double-fault and
> completely blinding the kernel's early SMP debugging
> capabilities.
>
> Moving it immediately after cpu_probe() ensures that the
> secondary CPU arms its $tp recovery mechanism at the earliest
> possible stage in its C entry path.
>
> I will absolutely adopt this suggestion and move it right
> after cpu_probe() in the next version. Thank you!
>
> >> +
> >> /*
> >> * irq will be enabled in loongson_smp_finish(), enabling it too
> >> * early is dangerous.
> >> diff --git a/arch/loongarch/kernel/switch.S b/arch/loongarch/kernel/switch.S
> >> index f377d8f5c51a..644348e05f6a 100644
> >> --- a/arch/loongarch/kernel/switch.S
> >> +++ b/arch/loongarch/kernel/switch.S
>
> ...
>
> >> + LONG_LPTR t0, tp, TASK_STACK
> > This should be "LONG_LPTR t0, tp, (TASK_STACK -
> > TASK_STRUCT_OFFSET)", otherwise it is wrong for 32BIT.
>
> Regarding the suggestion for (TASK_STACK - TASK_STRUCT_OFFSET)
> in switch.S:
>
> Thank you for bringing this up! With the definition of
> TASK_STRUCT_OFFSET in mind:
>
> #ifdef CONFIG_64BIT
> #define TASK_STRUCT_OFFSET 0
> #else
> #define TASK_STRUCT_OFFSET 2000
> #endif
>
> This is an incredibly sharp and critical catch for 32BIT
> architecture compatibility.
>
> I will update this line to:
> "LONG_LPTR t0, tp, (TASK_STACK - TASK_STRUCT_OFFSET)"
> in the next version.
>
> This is the incremental diff based on the original patch:
>
> ----->8-----
> diff --git
> a/Documentation/features/core/thread-info-in-task/arch-support.txt
> b/Documentation/features/core/thread-info-in-task/arch-support.txt
> index f3d744c76061..e26efdfbb6b4 100644
> --- a/Documentation/features/core/thread-info-in-task/arch-support.txt
> +++ b/Documentation/features/core/thread-info-in-task/arch-support.txt
> @@ -12,7 +12,7 @@
> | arm64: | ok |
> | csky: | TODO |
> | hexagon: | TODO |
> - | loongarch: | TODO |
> + | loongarch: | ok |
> | m68k: | TODO |
> | microblaze: | TODO |
> | mips: | TODO |
> diff --git a/arch/loongarch/include/asm/processor.h
> b/arch/loongarch/include/asm/processor.h
> index df927a4318cc..5d8e82b1dce7 100644
> --- a/arch/loongarch/include/asm/processor.h
> +++ b/arch/loongarch/include/asm/processor.h
> @@ -109,7 +109,7 @@ struct loongarch_vdso_info;
> */
> struct thread_struct {
> /* Main processor registers. */
> - unsigned long reg01, reg02, reg03, reg22; /* ra tp sp fp */
> + unsigned long reg01, reg03, reg22; /* ra sp fp */
> unsigned long reg23, reg24, reg25, reg26; /* s0-s3 */
> unsigned long reg27, reg28, reg29, reg30, reg31; /* s4-s8 */
>
> @@ -146,7 +146,6 @@ struct thread_struct {
> #define thread_saved_fp(tsk) (tsk->thread.sched_cfa)
>
> #define INIT_THREAD { \
> - .reg02 = (unsigned long)&init_task, \
> .reg03 = (unsigned long)&init_stack + sizeof(init_stack), \
> }
>
> diff --git a/arch/loongarch/include/asm/stackframe.h
> b/arch/loongarch/include/asm/stackframe.h
> index eeda5dcc982e..770db1084e8d 100644
> --- a/arch/loongarch/include/asm/stackframe.h
> +++ b/arch/loongarch/include/asm/stackframe.h
> @@ -191,15 +191,15 @@
> andi t0, t0, 0x3 /* extract pplv bit */
> beqz t0, 9f
>
> + cfi_st u0, PT_R21, \docfi
> + csrrd u0, PERCPU_BASE_KS
> +
> la_abs t1, __entry_task
> #ifdef CONFIG_SMP
> - csrrd t0, PERCPU_BASE_KS
> - LONG_ADD t1, t1, t0
> + LONG_ADD t1, t1, u0
> #endif
> LONG_L tp, t1, 0
>
> - cfi_st u0, PT_R21, \docfi
> - csrrd u0, PERCPU_BASE_KS
> 9:
> #ifdef CONFIG_KGDB
> li.w t0, CSR_CRMD_WE
> diff --git a/arch/loongarch/include/asm/thread_info.h
> b/arch/loongarch/include/asm/thread_info.h
> index 2c95a5134976..41eabe4fb647 100644
> --- a/arch/loongarch/include/asm/thread_info.h
> +++ b/arch/loongarch/include/asm/thread_info.h
> @@ -23,6 +23,7 @@
> */
> struct thread_info {
> unsigned long flags; /* low level flags */
> + unsigned long tp_value; /* thread pointer */
> __u32 cpu; /* current CPU */
> int preempt_count; /* 0 => preemptible, <0
> => BUG */
> struct pt_regs *regs;
> @@ -35,7 +36,7 @@ struct thread_info {
> */
> #define INIT_THREAD_INFO(tsk) \
> { \
> - .flags = 0, \
> + .flags = _TIF_FIXADE, \
> .cpu = 0, \
> .preempt_count = INIT_PREEMPT_COUNT, \
> }
> diff --git a/arch/loongarch/kernel/process.c
> b/arch/loongarch/kernel/process.c
> index 71c9c6468e60..2f916c4e0e8f 100644
> --- a/arch/loongarch/kernel/process.c
> +++ b/arch/loongarch/kernel/process.c
> @@ -226,9 +226,6 @@ int copy_thread(struct task_struct *p, const struct
> kernel_clone_args *args)
> if (clone_flags & CLONE_SETTLS)
> childregs->regs[2] = tls;
>
> - /* Set tp to the new task structure for context switching */
> - p->thread.reg02 = (unsigned long)p;
> -
> out:
> ptrace_hw_copy_thread(p);
> clear_tsk_thread_flag(p, TIF_USEDFPU);
> diff --git a/arch/loongarch/kernel/setup.c b/arch/loongarch/kernel/setup.c
> index 5d434c5612ab..7065d195f2da 100644
> --- a/arch/loongarch/kernel/setup.c
> +++ b/arch/loongarch/kernel/setup.c
> @@ -594,6 +594,7 @@ void __init setup_arch(char **cmdline_p)
> {
> cpu_probe();
> unwind_init();
> + entry_task_switch(&init_task);
>
> init_environ();
> efi_init();
> @@ -618,6 +619,4 @@ void __init setup_arch(char **cmdline_p)
> #ifdef CONFIG_KASAN
> kasan_init();
> #endif
> -
> - entry_task_switch(&init_task);
> }
> diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c
> index e8b0d2fc2a9a..4b74409a98a3 100644
> --- a/arch/loongarch/kernel/smp.c
> +++ b/arch/loongarch/kernel/smp.c
> @@ -665,6 +665,7 @@ asmlinkage void start_secondary(void)
> set_my_cpu_offset(per_cpu_offset(cpu));
>
> cpu_probe();
> + entry_task_switch(current);
> constant_clockevent_init();
> loongson_init_secondary();
>
> @@ -688,8 +689,6 @@ asmlinkage void start_secondary(void)
> */
> complete(&cpu_running);
>
> - entry_task_switch(current);
> -
> /*
> * irq will be enabled in loongson_smp_finish(), enabling it too
> * early is dangerous.
> diff --git a/arch/loongarch/kernel/switch.S b/arch/loongarch/kernel/switch.S
> index 644348e05f6a..33a10221d73a 100644
> --- a/arch/loongarch/kernel/switch.S
> +++ b/arch/loongarch/kernel/switch.S
> @@ -24,8 +24,8 @@ SYM_FUNC_START(__switch_to)
> LONG_SPTR t1, a0, (THREAD_CSRPRMD - TASK_STRUCT_OFFSET)
>
> cpu_save_nonscratch a0
> - LONG_SPTR a3, a0, (THREAD_SCHED_RA - TASK_STRUCT_OFFSET)
> - LONG_SPTR a4, a0, (THREAD_SCHED_CFA - TASK_STRUCT_OFFSET)
> + LONG_SPTR a2, a0, (THREAD_SCHED_RA - TASK_STRUCT_OFFSET)
> + LONG_SPTR a3, a0, (THREAD_SCHED_CFA - TASK_STRUCT_OFFSET)
>
> #if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_SMP)
> la t7, __stack_chk_guard
> @@ -36,7 +36,7 @@ SYM_FUNC_START(__switch_to)
> move tp, a1
> cpu_restore_nonscratch a1
>
> - LONG_LPTR t0, tp, TASK_STACK
> + LONG_LPTR t0, tp, (TASK_STACK - TASK_STRUCT_OFFSET)
> PTR_LI t1, _THREAD_SIZE
> PTR_ADD t0, t0, t1
> set_saved_sp t0, t1, t2
>
> Here is a test script:
>
> $ cat stress_test.sh
> #!/bin/bash
> set -e # Exit immediately if any command exits with a non-zero status
>
> echo "=== Starting LoongArch THREAD_INFO_IN_TASK Extreme Stress Testing ==="
> START_TIME=$(date)
>
> # Clear existing dmesg buffer and back it up safely to /tmp
> dmesg -c > /tmp/init_dmesg.log
>
> # 1. Core Context Switch Stress Test
> # Validates __switch_to() assembly and the 32-bit/64-bit structural
> offset calculations.
> echo "Running: --context stressor (10 mins)..."
> stress-ng --context $(nproc) --timeout 10m --metrics-brief
>
> # 2. Bad System Calls and Exception Path Stress Test
> # Validates handle_syscall and the __entry_task recovery path during
> exception entry.
> # Fixed option to use the unambiguous '--sysbadaddr'
> echo "Running: --sysbadaddr stressor (10 mins)..."
> stress-ng --sysbadaddr $(nproc) --timeout 10m
>
> # 3. Page Fault and Stack Stress Test
> # Validates register reuse optimization (u0/PERCPU_BASE_KS) within the
> SAVE_SOME macro.
> echo "Running: --fault stressor (10 mins)..."
> stress-ng --fault $(nproc) --timeout 10m
>
> # 4. Multi-Thread Cloning and Destruction Stress Test
> # Validates the preservation of tp_value and the correctness of
> copy_thread().
> echo "Running: --pthread stressor (10 mins)..."
> stress-ng --pthread $(nproc) --timeout 10m
>
> # 5. Ultimate Mixed Scheduling Matrix Test
> # Simulates an extremely hostile system environment with high
> concurrency (20 mins).
> echo "Running: Mixed Matrix (--schedmix + --yield) (20 mins)..."
> stress-ng --schedmix $(nproc) --yield $(nproc) --timeout 20m --metrics
>
> END_TIME=$(date)
> echo "=== All stress-ng commands completed successfully ==="
> echo "Start Time: $START_TIME"
> echo "End Time: $END_TIME"
>
> # 2. Automated Kernlog Integrity Check
> # Scans dmesg for hidden kernel regressions, warnings, or silent corruption.
> echo "=== Analyzing kernel dmesg logs... ==="
> if sudo dmesg | grep -qEi "oops|panic|warning|bug|recursive|tainted"; then
> echo "❌ WARNING: System survived but dmesg contains kernel errors!
> Please check the logs below:"
> sudo dmesg | grep -Ei "oops|panic|warning|bug|recursive|tainted" -C 5
> else
> echo "✅ SUCCESS: dmesg remains perfectly silent! No Oops, Warnings,
> or Panics found."
> echo "The patch successfully passed the 1-hour stress testing suite!"
> fi
>
> Here are the test steps:
>
> sudo dnf install -y stress-ng
> chmod +x stress_test.sh
> sudo ./stress_test.sh
>
> Here is the test result:
>
> $ sudo ./stress_test.sh
> === Starting LoongArch THREAD_INFO_IN_TASK Extreme Stress Testing ===
> Running: --context stressor (10 mins)...
> stress-ng: info: [2719] setting to a 10 mins run per stressor
> stress-ng: info: [2719] dispatching hogs: 8 context
> stress-ng: metrc: [2719] stressor bogo ops real time usr time
> sys time bogo ops/s bogo ops/s
> stress-ng: metrc: [2719] (secs) (secs)
> (secs) (real time) (usr+sys time)
> stress-ng: metrc: [2719] context 41308615 600.00 2226.94
> 2571.93 68847.69 8607.98
> stress-ng: info: [2719] skipped: 0
> stress-ng: info: [2719] passed: 8: context (8)
> stress-ng: info: [2719] failed: 0
> stress-ng: info: [2719] metrics untrustworthy: 0
> stress-ng: info: [2719] successful run completed in 10 mins
> Running: --sysbadaddr stressor (10 mins)...
> stress-ng: info: [2742] setting to a 10 mins run per stressor
> stress-ng: info: [2742] dispatching hogs: 8 sysbadaddr
> stress-ng: info: [2742] skipped: 0
> stress-ng: info: [2742] passed: 8: sysbadaddr (8)
> stress-ng: info: [2742] failed: 0
> stress-ng: info: [2742] metrics untrustworthy: 0
> stress-ng: info: [2742] successful run completed in 10 mins
> Running: --fault stressor (10 mins)...
> stress-ng: info: [1090732] setting to a 10 mins run per stressor
> stress-ng: info: [1090732] dispatching hogs: 8 fault
> stress-ng: info: [1090732] skipped: 0
> stress-ng: info: [1090732] passed: 8: fault (8)
> stress-ng: info: [1090732] failed: 0
> stress-ng: info: [1090732] metrics untrustworthy: 0
> stress-ng: info: [1090732] successful run completed in 10 mins
> Running: --pthread stressor (10 mins)...
> stress-ng: info: [1090760] setting to a 10 mins run per stressor
> stress-ng: info: [1090760] dispatching hogs: 8 pthread
> stress-ng: info: [1090760] skipped: 0
> stress-ng: info: [1090760] passed: 8: pthread (8)
> stress-ng: info: [1090760] failed: 0
> stress-ng: info: [1090760] metrics untrustworthy: 0
> stress-ng: info: [1090760] successful run completed in 10 mins
> Running: Mixed Matrix (--schedmix + --yield) (20 mins)...
> stress-ng: info: [3131692] setting to a 20 mins run per stressor
> stress-ng: info: [3131692] dispatching hogs: 8 schedmix, 8 yield
> stress-ng: metrc: [3131692] stressor bogo ops real time usr time
> sys time bogo ops/s bogo ops/s CPU used per RSS Max
> stress-ng: metrc: [3131692] (secs) (secs)
> (secs) (real time) (usr+sys time) instance (%) (KB)
> stress-ng: metrc: [3131692] schedmix 6577020 1200.04 1817.35
> 5090.05 5480.67 952.17 71.95 3392
> stress-ng: metrc: [3131692] yield 2861718847 1200.00 733.75
> 1937.44 2384764.49 1071325.09 27.82 3360
> stress-ng: metrc: [3131692] miscellaneous metrics:
> stress-ng: metrc: [3131692] yield 6672.42 ns duration per
> sched_yield call (harmonic mean of 8 instances)
> stress-ng: info: [3131692] skipped: 0
> stress-ng: info: [3131692] passed: 16: schedmix (8) yield (8)
> stress-ng: info: [3131692] failed: 0
> stress-ng: info: [3131692] metrics untrustworthy: 0
> stress-ng: info: [3131692] successful run completed in 20 mins
> === All stress-ng commands completed successfully ===
> Start Time: Wed Jun 3 09:03:43 AM CST 2026
> End Time: Wed Jun 3 10:03:44 AM CST 2026
> === Analyzing kernel dmesg logs... ===
> ✅ SUCCESS: dmesg remains perfectly silent! No Oops, Warnings, or Panics
> found.
> The patch successfully passed the 1-hour stress testing suite!
>
> I will send formal patch v1 next week.
>
> Thanks,
> Tiezhu
>
>
next prev parent reply other threads:[~2026-06-03 14:24 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-28 7:20 [RFC PATCH 0/3] Move thread_info into task_struct for LoongArch Tiezhu Yang
2026-04-28 7:20 ` [RFC PATCH 1/3] LoongArch: Implement CONFIG_THREAD_INFO_IN_TASK Tiezhu Yang
2026-06-01 13:46 ` Huacai Chen
2026-06-03 2:30 ` Tiezhu Yang
2026-06-03 14:24 ` Huacai Chen [this message]
2026-06-04 2:26 ` Tiezhu Yang
2026-06-04 5:05 ` Tiezhu Yang
2026-06-04 6:26 ` Huacai Chen
2026-04-28 7:20 ` [RFC PATCH 2/3] LoongArch: BPF: Inline bpf_get_current_task{_btf}() helpers Tiezhu Yang
2026-04-28 7:20 ` [RFC PATCH 3/3] LoongArch: BPF: Inline bpf_get_smp_processor_id() helper Tiezhu Yang
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