[Devel] [PATCH vz7 4/5] ms/sched/x86: Add 'struct inactive_task_frame' to better document the sleeping task stack frame

[Konstantin Khorenko]

From: Brian Gerst <brgerst at gmail.com>

Add 'struct inactive_task_frame', which defines the layout of the stack for
a sleeping process.  For now, the only defined field is the BP register
(frame pointer).

Signed-off-by: Brian Gerst <brgerst at gmail.com>
Reviewed-by: Josh Poimboeuf <jpoimboe at redhat.com>
Cc: Andy Lutomirski <luto at kernel.org>
Cc: Borislav Petkov <bp at alien8.de>
Cc: Denys Vlasenko <dvlasenk at redhat.com>
Cc: H. Peter Anvin <hpa at zytor.com>
Cc: Linus Torvalds <torvalds at linux-foundation.org>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Thomas Gleixner <tglx at linutronix.de>
Link: http://lkml.kernel.org/r/1471106302-10159-4-git-send-email-brgerst@gmail.com
Signed-off-by: Ingo Molnar <mingo at kernel.org>

(cherry picked from commit 7b32aeadbc95d4a41402c1c0da6aa3ab51af4c10)
In the scope of https://jira.sw.ru/browse/HCI-171

Signed-off-by: Konstantin Khorenko <khorenko at virtuozzo.com>
---
 arch/x86/include/asm/stacktrace.h | 4 ++--
 arch/x86/include/asm/switch_to.h  | 5 +++++
 arch/x86/kernel/kgdb.c            | 3 ++-
 arch/x86/kernel/process.c         | 3 ++-
 4 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/stacktrace.h b/arch/x86/include/asm/stacktrace.h
index f8a383338352..a4fe84fd293c 100644
--- a/arch/x86/include/asm/stacktrace.h
+++ b/arch/x86/include/asm/stacktrace.h
@@ -8,6 +8,7 @@
 
 #include <linux/uaccess.h>
 #include <linux/ptrace.h>
+#include <asm/switch_to.h>
 
 enum stack_type {
 	STACK_TYPE_UNKNOWN,
@@ -58,8 +59,7 @@ get_frame_pointer(struct task_struct *task, struct pt_regs *regs)
 	if (task == current)
 		return __builtin_frame_address(0);
 
-	/* bp is the last reg pushed by switch_to */
-	return (unsigned long *)*(unsigned long *)task->thread.sp;
+	return ((struct inactive_task_frame *)task->thread.sp)->bp;
 }
 #else
 static inline unsigned long *
diff --git a/arch/x86/include/asm/switch_to.h b/arch/x86/include/asm/switch_to.h
index 4ec45b3abba1..c8950d57a8f3 100644
--- a/arch/x86/include/asm/switch_to.h
+++ b/arch/x86/include/asm/switch_to.h
@@ -8,6 +8,11 @@ struct tss_struct;
 void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
 		      struct tss_struct *tss);
 
+/* data that is pointed to by thread.sp */
+struct inactive_task_frame {
+	unsigned long bp;
+};
+
 #ifdef CONFIG_X86_32
 
 #ifdef CONFIG_CC_STACKPROTECTOR
diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
index 7ec1d5f8d283..9b4e1dd2e3aa 100644
--- a/arch/x86/kernel/kgdb.c
+++ b/arch/x86/kernel/kgdb.c
@@ -49,6 +49,7 @@
 #include <asm/apicdef.h>
 #include <asm/apic.h>
 #include <asm/nmi.h>
+#include <asm/switch_to.h>
 
 struct dbg_reg_def_t dbg_reg_def[DBG_MAX_REG_NUM] =
 {
@@ -165,7 +166,7 @@ void sleeping_thread_to_gdb_regs(unsigned long *gdb_regs, struct task_struct *p)
 	gdb_regs[GDB_DX]	= 0;
 	gdb_regs[GDB_SI]	= 0;
 	gdb_regs[GDB_DI]	= 0;
-	gdb_regs[GDB_BP]	= *(unsigned long *)p->thread.sp;
+	gdb_regs[GDB_BP]	= ((struct inactive_task_frame *)p->thread.sp)->bp;
 #ifdef CONFIG_X86_32
 	gdb_regs[GDB_DS]	= __KERNEL_DS;
 	gdb_regs[GDB_ES]	= __KERNEL_DS;
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 1f2f0d1545bc..79c941f4c72c 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -31,6 +31,7 @@
 #include <asm/nmi.h>
 #include <asm/mce.h>
 #include <asm/spec_ctrl.h>
+#include <asm/switch_to.h>
 
 /*
  * per-CPU TSS segments. Threads are completely 'soft' on Linux,
@@ -688,7 +689,7 @@ unsigned long get_wchan(struct task_struct *p)
 	if (sp < bottom || sp > top)
 		return 0;
 
-	fp = READ_ONCE_NOCHECK(*(unsigned long *)sp);
+	fp = READ_ONCE_NOCHECK(((struct inactive_task_frame *)sp)->bp);
 	do {
 		if (fp < bottom || fp > top)
 			return 0;
-- 
2.15.1