tile: improve stack backtrace

This commit fixes a number of issues with the tile backtrace code.

- Don't try to identify userspace shared object or executable paths
  if we are doing a backtrace from an interrupt; it's not legal,
  and also unlikely to be interesting.  Likewise, don't try to do
  it for other address spaces, since d_path() assumes it is being
  called in "current" context.

- Move "in_backtrace" from thread_struct to thread_info.
  This way we can access it even if our stack thread_info has been
  clobbered, which makes backtracing more robust.

- Avoid using "current" directly when testing for is_sigreturn().
  Since "current" may be corrupt, we're better off using kbt->task
  explicitly to look up the vdso_base for the current task.
  Conveniently, this simplifies the internal APIs (we only need
  one is_sigreturn() function now).

- Avoid bogus "Odd fault" warning when pc/sp/ex1 are all zero,
  as is true for kernel threads above the last frame.

- Hook into Tejun Heo's dump_stack() framework in lib/dump_stack.c.

- Write last entry in save_stack_trace() as ULONG_MAX, not zero,
  since ftrace (at least) relies on finding that marker.

- Implement save_stack_trace_regs() and save_strack_trace_user(),
  and set CONFIG_USER_STACKTRACE_SUPPORT.

Signed-off-by: Chris Metcalf <cmetcalf@ezchip.com>

3 files changed, 6 insertions, 10 deletions

diff --git a/arch/tile/include/asm/processor.h b/arch/tile/include/asm/processor.h
index dd4f9f17e30a..139dfdee0134 100644
--- a/arch/tile/include/asm/processor.h
+++ b/arch/tile/include/asm/processor.h
@@ -111,8 +111,6 @@ struct thread_struct {
 	unsigned long long interrupt_mask;
 	/* User interrupt-control 0 state */
 	unsigned long intctrl_0;
-	/* Is this task currently doing a backtrace? */
-	bool in_backtrace;
 	/* Any other miscellaneous processor state bits */
 	unsigned long proc_status;
 #if !CHIP_HAS_FIXED_INTVEC_BASE()
diff --git a/arch/tile/include/asm/stack.h b/arch/tile/include/asm/stack.h
index 0e9d382a2d45..c3cb42615a9f 100644
--- a/arch/tile/include/asm/stack.h
+++ b/arch/tile/include/asm/stack.h
@@ -58,17 +58,14 @@ extern int KBacktraceIterator_end(struct KBacktraceIterator *kbt);
 /* Advance to the next frame. */
 extern void KBacktraceIterator_next(struct KBacktraceIterator *kbt);
 
+/* Dump just the contents of the pt_regs structure. */
+extern void tile_show_regs(struct pt_regs *);
+
 /*
  * Dump stack given complete register info. Use only from the
  * architecture-specific code; show_stack()
- * and dump_stack() (in entry.S) are architecture-independent entry points.
+ * and dump_stack() are architecture-independent entry points.
  */
-extern void tile_show_stack(struct KBacktraceIterator *, int headers);
-
-/* Dump stack of current process, with registers to seed the backtrace. */
-extern void dump_stack_regs(struct pt_regs *);
-
-/* Helper method for assembly dump_stack(). */
-extern void _dump_stack(int dummy, ulong pc, ulong lr, ulong sp, ulong r52);
+extern void tile_show_stack(struct KBacktraceIterator *);
 
 #endif /* _ASM_TILE_STACK_H */
diff --git a/arch/tile/include/asm/thread_info.h b/arch/tile/include/asm/thread_info.h
index f804c39a5e4d..dc1fb28d9636 100644
--- a/arch/tile/include/asm/thread_info.h
+++ b/arch/tile/include/asm/thread_info.h
@@ -42,6 +42,7 @@ struct thread_info {
 	unsigned long		unalign_jit_tmp[4]; /* temp r0..r3 storage */
 	void __user		*unalign_jit_base; /* unalign fixup JIT base */
 #endif
+	bool in_backtrace;			/* currently doing backtrace? */
 };
 
 /*