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    Subject[PATCH 8/9] stacktrace: implement save_stack_trace_quick()
    Date
    Implement save_stack_trace_quick() which only considers the usual
    contexts (ie. thread and irq) and doesn't handle links between
    different contexts - if %current is in irq context, only backtrace in
    the irq stack is considered.

    This is subset of dump_trace() done in much simpler way. It's
    intended to be used in hot paths where the overhead of dump_trace()
    can be too heavy.

    Signed-off-by: Tejun Heo <tj@kernel.org>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: "H. Peter Anvin" <hpa@zytor.com>
    ---
    arch/x86/include/asm/stacktrace.h | 2 +
    arch/x86/kernel/stacktrace.c | 40 +++++++++++++++++++++++++++++++++++++
    include/linux/stacktrace.h | 6 +++++
    kernel/stacktrace.c | 6 +++++
    4 files changed, 54 insertions(+), 0 deletions(-)

    diff --git a/arch/x86/include/asm/stacktrace.h b/arch/x86/include/asm/stacktrace.h
    index 70bbe39..06bbdfc 100644
    --- a/arch/x86/include/asm/stacktrace.h
    +++ b/arch/x86/include/asm/stacktrace.h
    @@ -50,9 +50,11 @@ void dump_trace(struct task_struct *tsk, struct pt_regs *regs,
    #ifdef CONFIG_X86_32
    #define STACKSLOTS_PER_LINE 8
    #define get_bp(bp) asm("movl %%ebp, %0" : "=r" (bp) :)
    +#define get_irq_stack_end() 0
    #else
    #define STACKSLOTS_PER_LINE 4
    #define get_bp(bp) asm("movq %%rbp, %0" : "=r" (bp) :)
    +#define get_irq_stack_end() (unsigned long)this_cpu_read(irq_stack_ptr)
    #endif

    #ifdef CONFIG_FRAME_POINTER
    diff --git a/arch/x86/kernel/stacktrace.c b/arch/x86/kernel/stacktrace.c
    index fdd0c64..f53ec547 100644
    --- a/arch/x86/kernel/stacktrace.c
    +++ b/arch/x86/kernel/stacktrace.c
    @@ -81,6 +81,46 @@ void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
    }
    EXPORT_SYMBOL_GPL(save_stack_trace_tsk);

    +#ifdef CONFIG_FRAME_POINTER
    +void save_stack_trace_quick(struct stack_trace *trace)
    +{
    + const unsigned long stk_sz = THREAD_SIZE - sizeof(struct stack_frame);
    + unsigned long tstk = (unsigned long)current_thread_info();
    + unsigned long istk = get_irq_stack_end();
    + unsigned long last_bp = 0;
    + unsigned long bp, stk;
    +
    + get_bp(bp);
    +
    + if (bp > tstk && bp <= tstk + stk_sz)
    + stk = tstk;
    + else if (istk && (bp > istk && bp <= stk_sz))
    + stk = istk;
    + else
    + goto out;
    +
    + while (bp > last_bp && bp <= stk + stk_sz) {
    + struct stack_frame *frame = (struct stack_frame *)bp;
    + unsigned long ret_addr = frame->return_address;
    +
    + if (!trace->skip) {
    + if (trace->nr_entries >= trace->max_entries)
    + return;
    + trace->entries[trace->nr_entries++] = ret_addr;
    + } else {
    + trace->skip--;
    + }
    +
    + last_bp = bp;
    + bp = (unsigned long)frame->next_frame;
    + }
    +out:
    + if (trace->nr_entries < trace->max_entries)
    + trace->entries[trace->nr_entries++] = ULONG_MAX;
    +}
    +EXPORT_SYMBOL_GPL(save_stack_trace_quick);
    +#endif
    +
    /* Userspace stacktrace - based on kernel/trace/trace_sysprof.c */

    struct stack_frame_user {
    diff --git a/include/linux/stacktrace.h b/include/linux/stacktrace.h
    index 115b570..d5b16c4 100644
    --- a/include/linux/stacktrace.h
    +++ b/include/linux/stacktrace.h
    @@ -19,6 +19,12 @@ extern void save_stack_trace_regs(struct pt_regs *regs,
    extern void save_stack_trace_tsk(struct task_struct *tsk,
    struct stack_trace *trace);

    +/*
    + * Saves only trace from the current context. Doesn't handle exception
    + * stacks or verify text address.
    + */
    +extern void save_stack_trace_quick(struct stack_trace *trace);
    +
    extern void print_stack_trace(struct stack_trace *trace, int spaces);

    #ifdef CONFIG_USER_STACKTRACE_SUPPORT
    diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c
    index 00fe55c..4760949 100644
    --- a/kernel/stacktrace.c
    +++ b/kernel/stacktrace.c
    @@ -31,6 +31,12 @@ EXPORT_SYMBOL_GPL(print_stack_trace);
    * (whenever this facility is utilized - for example by procfs):
    */
    __weak void
    +save_stack_trace_quick(struct stack_trace *trace)
    +{
    + WARN_ONCE(1, KERN_INFO "save_stack_trace_quick() not implemented yet.\n");
    +}
    +
    +__weak void
    save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
    {
    WARN_ONCE(1, KERN_INFO "save_stack_trace_tsk() not implemented yet.\n");
    --
    1.7.3.1


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