Export kernel backtrace in /proc/<pid>/task/<tid>/stack. Useful when debugging
deadlocks.

This somewhat duplicates functionality of SysRq-T, but is less intrusive to
the system operation and can be used in the scripts.

Exporting kernel stack of a thread is probably unsound security-wise. Use with
care.

Instead of adding yet another architecture specific function to output thread
stack through seq_file API, it introduces "iterator"

void do_with_stack(struct task_struct *tsk, 
		   int (*actor)(int, void *, void *, void *), void *opaque)

that has to be implemented by each architecture, so that generic code can
iterate over stack frames in architecture-independent way.

lib/do_with_stack.c is provided for archituctures that don't implement their
own. It is based on __builtin_{frame,return}_address().




 arch/i386/Kconfig.debug  |    9 ++++++
 arch/i386/kernel/traps.c |   42 ++++++++++++++++++++++++++++
 fs/proc/base.c           |   69 +++++++++++++++++++++++++++++++++++++++++++++++
 lib/Makefile             |    2 -
 lib/do_with_stack.c      |   14 +++++++++
 5 files changed, 135 insertions(+), 1 deletion(-)

diff -puN fs/proc/base.c~proc-stack fs/proc/base.c
--- bk-linux/fs/proc/base.c~proc-stack	2004-11-08 15:08:14.397853776 +0300
+++ bk-linux-nikita/fs/proc/base.c	2004-11-08 15:08:14.571827328 +0300
@@ -96,6 +96,9 @@ enum pid_directory_inos {
 	PROC_TID_ATTR_EXEC,
 	PROC_TID_ATTR_FSCREATE,
 #endif
+#ifdef CONFIG_PROC_STACK
+	PROC_TID_STACK,
+#endif
 	PROC_TID_FD_DIR = 0x8000,	/* 0x8000-0xffff */
 };
 
@@ -157,6 +160,9 @@ static struct pid_entry tid_base_stuff[]
 #ifdef CONFIG_SCHEDSTATS
 	E(PROC_TID_SCHEDSTAT, "schedstat",S_IFREG|S_IRUGO),
 #endif
+#ifdef CONFIG_PROC_STACK
+	E(PROC_TID_STACK,      "stack",   S_IFREG|S_IRUGO),
+#endif
 	{0,0,NULL,0}
 };
 
@@ -425,6 +431,63 @@ static int proc_pid_schedstat(struct tas
 }
 #endif
 
+#ifdef CONFIG_PROC_STACK
+extern void do_with_stack(struct task_struct *tsk,
+			  int (*actor)(int, void *, void *, void *),
+			  void *opaque);
+
+struct print_stack_arg {
+	char *buf;
+	int   off;
+};
+
+#define PRINT(buf, off, format, ...)				\
+	(off) += snprintf((buf) + (off),			\
+			  max_t(int, PAGE_SIZE - (off), 0), 	\
+			  (format) , ## __VA_ARGS__)
+
+static int stack_actor(int frameno, void *frame, void *address, void *cookie)
+{
+	struct print_stack_arg *arg;
+	int off;
+
+	char         *modname;
+	const char   *name;
+	unsigned long size;
+	unsigned long offset;
+	char          namebuf[128];
+
+	arg = cookie;
+
+	if (arg->off > PAGE_SIZE)
+		return 0;
+
+	name = kallsyms_lookup((unsigned long)address,
+			       &size, &offset, &modname, namebuf);
+	off = arg->off;
+	PRINT(arg->buf, off, "%02i: %p %p", frameno, frame, address);
+	if (name != NULL)
+		PRINT(arg->buf, off, " %s+%#lx/%#lx", name, offset, size);
+	PRINT(arg->buf, off, "\n");
+	arg->off = min_t(int, off, PAGE_SIZE);
+	return 0;
+}
+
+#undef PRINT
+
+static int proc_pid_stack(struct task_struct *task, char *buffer)
+{
+	struct print_stack_arg cookie;
+
+	cookie.buf = buffer;
+	cookie.off = 0;
+
+	do_with_stack(task, stack_actor, &cookie);
+	return cookie.off;
+}
+/* CONFIG_PROC_STACK */
+#endif
+
 /************************************************************************/
 /*                       Here the fs part begins                        */
 /************************************************************************/
@@ -1382,6 +1445,12 @@ static struct dentry *proc_pident_lookup
 			ei->op.proc_read = proc_pid_schedstat;
 			break;
 #endif
+#ifdef CONFIG_PROC_STACK
+		case PROC_TID_STACK:
+			inode->i_fop = &proc_info_file_operations;
+			ei->op.proc_read = proc_pid_stack;
+			break;
+#endif
 		default:
 			printk("procfs: impossible type (%d)",p->type);
 			iput(inode);
diff -puN arch/i386/kernel/traps.c~proc-stack arch/i386/kernel/traps.c
--- bk-linux/arch/i386/kernel/traps.c~proc-stack	2004-11-08 15:08:14.422849976 +0300
+++ bk-linux-nikita/arch/i386/kernel/traps.c	2004-11-08 15:08:14.573827024 +0300
@@ -170,6 +170,48 @@ static inline unsigned long print_contex
 	return ebp;
 }
 
+/*
+ * do_with_stack()
+ *
+ * Iterate over stack frames of @tsk from innermost upward.
+ *
+ * @tsk task which stack is traversed
+ *
+ * @actor is called on each stack frame with 4 parameters:
+ *
+ *    frameno,   1-based, starting from innermost.
+ *
+ *    frameaddr, address on the stack
+ *
+ *    address,   return address
+ *
+ *    cookie,    arbitrary cookie passed to the do_with_stack()
+ *
+ * @cookie to be passed to the @actor
+ *
+ */
+void do_with_stack(struct task_struct *tsk,
+		   int (*actor)(int, void *, void *, void *), void *opaque)
+{
+	unsigned long *esp = (unsigned long *)tsk->thread.esp;
+	unsigned long  addr;
+	int i;
+
+	/* User space on another CPU? */
+	if ((tsk->thread.esp ^ (unsigned long)tsk->thread_info) & (PAGE_MASK<<1))
+		return;
+	i = 1;
+	while (((long) esp & (THREAD_SIZE-1)) != 0) {
+		addr = *esp;
+		if (kernel_text_address(addr)) {
+			actor(i, esp, (void *)addr, opaque);
+			i ++;
+		}
+		esp ++;
+	}
+}
+
+
 void show_trace(struct task_struct *task, unsigned long * stack)
 {
 	unsigned long ebp;
diff -puN lib/Makefile~proc-stack lib/Makefile
--- bk-linux/lib/Makefile~proc-stack	2004-11-08 15:08:14.447846176 +0300
+++ bk-linux-nikita/lib/Makefile	2004-11-08 15:08:14.573827024 +0300
@@ -5,7 +5,7 @@
 lib-y := errno.o ctype.o string.o vsprintf.o cmdline.o \
 	 bust_spinlocks.o rbtree.o radix-tree.o dump_stack.o \
 	 kobject.o kref.o idr.o div64.o parser.o int_sqrt.o \
-	 bitmap.o extable.o kobject_uevent.o
+	 bitmap.o extable.o kobject_uevent.o do_with_stack.o
 
 ifeq ($(CONFIG_DEBUG_KOBJECT),y)
 CFLAGS_kobject.o += -DDEBUG
diff -puN /dev/null lib/do_with_stack.c
--- /dev/null	2004-04-06 17:27:52.000000000 +0400
+++ bk-linux-nikita/lib/do_with_stack.c	2004-11-08 15:08:14.573827024 +0300
@@ -0,0 +1,14 @@
+/*
+ * Provide a default do_with_stack() function for architectures
+ * which don't implement their own.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+
+void do_with_stack(struct task_struct *tsk, 
+		   int (*actor)(int, void *, void *, void *), void *o)
+{
+	actor(1, __builtin_frame_address(0), __builtin_return_address(0), o);
+	actor(2, __builtin_frame_address(1), __builtin_return_address(1), o);
+}
diff -puN arch/i386/Kconfig~proc-stack arch/i386/Kconfig
diff -puN lib/Kconfig.debug~proc-stack lib/Kconfig.debug
diff -puN arch/i386/Kconfig.debug~proc-stack arch/i386/Kconfig.debug
--- bk-linux/arch/i386/Kconfig.debug~proc-stack	2004-11-08 15:08:14.567827936 +0300
+++ bk-linux-nikita/arch/i386/Kconfig.debug	2004-11-08 15:08:14.591824288 +0300
@@ -67,4 +67,13 @@ config X86_MPPARSE
 
 source "arch/i386/Kconfig.kgdb"
 
+config PROC_STACK
+	bool "Export kernel stack in the /proc/pid/stack"
+	depends on DEBUG_KERNEL
+    default n
+    help
+      If you say Y here, new file /proc/pid/stack will appear that contains
+      current kernel backtrace of given process. This may have security
+      implications. If unsure say N.
+
 endmenu

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