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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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