Re: [PATCH 4/5] UML - Simplify helper stack handling

Andrew Morton
2007-06-28T06:37:30Z

So I'm running the generic version of this on i386 with 8k stacks (below),
with a quick LTP run.

Holy cow, either we use a _lot_ of stack or these numbers are off:

vmm:/home/akpm> dmesg -s 1000000|grep 'bytes left'
khelper used greatest stack depth: 7176 bytes left
khelper used greatest stack depth: 7064 bytes left
khelper used greatest stack depth: 6840 bytes left
khelper used greatest stack depth: 6812 bytes left
hostname used greatest stack depth: 6636 bytes left
uname used greatest stack depth: 6592 bytes left
uname used greatest stack depth: 6284 bytes left
hotplug used greatest stack depth: 5568 bytes left
rpc.nfsd used greatest stack depth: 5136 bytes left
chown02 used greatest stack depth: 4956 bytes left
fchown01 used greatest stack depth: 4892 bytes left

That's the sum of process stack and interrupt stack, but I doubt if this
little box is using much interrupt stack space.

No wonder people are still getting stack overflows with 4k stacks...

From: Jeff Dike <jdike@addtoit.com>

Add generic exit-time stack-depth checking to CONFIG_DEBUG_STACK_USAGE.

This also adds UML support.

Tested on UML and i386.

[akpm@linux-foundation.org: cleanups, speedups, tweaks]
Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

arch/um/Kconfig.debug | 9 +++++++++
arch/um/defconfig | 1 +
include/asm-um/thread_info.h | 9 +++++++++
kernel/exit.c | 29 +++++++++++++++++++++++++++++
4 files changed, 48 insertions(+)

diff -puN arch/um/Kconfig.debug~add-generic-exit-time-stack-depth-checking-to-config_debug_stack_usage arch/um/Kconfig.debug
--- a/arch/um/Kconfig.debug~add-generic-exit-time-stack-depth-checking-to-config_debug_stack_usage
+++ a/arch/um/Kconfig.debug
@@ -47,4 +47,13 @@ config GCOV
If you're involved in UML kernel development and want to use gcov,
say Y. If you're unsure, say N.

+config DEBUG_STACK_USAGE
+ bool "Stack utilization instrumentation"
+ default N
+ help
+ Track the maximum kernel stack usage - this will look at each
+ kernel stack at process exit and log it if it's the deepest
+ stack seen so far.
+
+ This option will slow down process creation and destruction somewhat.
endmenu
diff -puN arch/um/defconfig~add-generic-exit-time-stack-depth-checking-to-config_debug_stack_usage arch/um/defconfig
--- a/arch/um/defconfig~add-generic-exit-time-stack-depth-checking-to-config_debug_stack_usage
+++ a/arch/um/defconfig
@@ -527,3 +527,4 @@ CONFIG_FORCED_INLINING=y
# CONFIG_RCU_TORTURE_TEST is not set
# CONFIG_GPROF is not set
# CONFIG_GCOV is not set
+# CONFIG_DEBUG_STACK_USAGE is not set
diff -puN include/asm-um/thread_info.h~add-generic-exit-time-stack-depth-checking-to-config_debug_stack_usage include/asm-um/thread_info.h
--- a/include/asm-um/thread_info.h~add-generic-exit-time-stack-depth-checking-to-config_debug_stack_usage
+++ a/include/asm-um/thread_info.h
@@ -52,10 +52,19 @@ static inline struct thread_info *curren
return ti;
}

+#ifdef CONFIG_DEBUG_STACK_USAGE
+
+#define alloc_thread_info(tsk) \
+ ((struct thread_info *) __get_free_pages(GFP_KERNEL | __GFP_ZERO, \
+ CONFIG_KERNEL_STACK_ORDER))
+#else
+
/* thread information allocation */
#define alloc_thread_info(tsk) \
((struct thread_info *) __get_free_pages(GFP_KERNEL, \
CONFIG_KERNEL_STACK_ORDER))
+#endif
+
#define free_thread_info(ti) \
free_pages((unsigned long)(ti),CONFIG_KERNEL_STACK_ORDER)

diff -puN kernel/exit.c~add-generic-exit-time-stack-depth-checking-to-config_debug_stack_usage kernel/exit.c
--- a/kernel/exit.c~add-generic-exit-time-stack-depth-checking-to-config_debug_stack_usage
+++ a/kernel/exit.c
@@ -868,6 +868,34 @@ static void exit_notify(struct task_stru
release_task(tsk);
}

+#ifdef CONFIG_DEBUG_STACK_USAGE
+static void check_stack_usage(void)
+{
+ static DEFINE_SPINLOCK(low_water_lock);
+ static int lowest_to_date = THREAD_SIZE;
+ unsigned long *n = end_of_stack(current);
+ unsigned long free;
+
+ while (*n == 0)
+ n++;
+ free = (unsigned long)n - (unsigned long)end_of_stack(current);
+
+ if (free >= lowest_to_date)
+ return;
+
+ spin_lock(&low_water_lock);
+ if (free < lowest_to_date) {
+ printk(KERN_WARNING "%s used greatest stack depth: %lu bytes "
+ "left\n",
+ current->comm, free);
+ lowest_to_date = free;
+ }
+ spin_unlock(&low_water_lock);
+}
+#else
+static inline void check_stack_usage(void) {}
+#endif
+
fastcall NORET_TYPE void do_exit(long code)
{
struct task_struct *tsk = current;
@@ -959,6 +987,7 @@ fastcall NORET_TYPE void do_exit(long co
exit_sem(tsk);
__exit_files(tsk);
__exit_fs(tsk);
+ check_stack_usage();
exit_thread();
cpuset_exit(tsk);
exit_keys(tsk);
_