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Date: Fri, 7 Nov 2008 08:59:25 +0100
From: Ingo Molnar <mingo@...e.hu>
To: Alexey Dobriyan <adobriyan@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: Ken Chen <kenchen@...gle.com>, linux-kernel@...r.kernel.org,
Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [patch] add /proc/pid/stack to dump task's stack trace
* Ingo Molnar <mingo@...e.hu> wrote:
> > > + * buffer size used for proc read. See proc_info_read().
> > > + * 4K page size but our output routines use some slack for overruns
> > > + */
> > > +#define PROC_BLOCK_SIZE (3*1024)
>
> That sounds like a proper limit - the hard limit for this particular
> printout function is 4096-170, so we are well within the
> PROC_BLOCK_SIZE range.
ok, i've added Ken's patch to tip/core/stacktrace and started testing
it.
Alexey, i've added your Acked-by because you appeared to like the
patch - let me know if i should remove it.
i've done a few finishing touches to the patch as well - see the end
result below.
Andrew, i remember that you found some sort of problem (crashes?) with
stack-dumping tasks that are running on another CPU (or something like
that) - do you remember the specifics? Could we run into any of those
problems with the patch below, on some rare architecture?
Ingo
------------------->
>From d3d23f82adeb5ec8a9546747d1df058dcaad0589 Mon Sep 17 00:00:00 2001
From: Ken Chen <kenchen@...gle.com>
Date: Thu, 6 Nov 2008 16:30:23 -0800
Subject: [PATCH] stacktrace: add /proc/<pid>/stack to dump task's stack trace
Impact: add the new (root-only) /proc/<pid>/stack debug facility
This patch adds the ability to query a task's current stack trace via
/proc/<pid>/stack.
It is considered to be more useful than /proc/pid/wchan as it provides
full stack trace instead of single depth.
It is also more useful than sysrq-t because it does not overflow the
dmesg like sysrq-t often does, can be read in a finegrained per-task
way and can be read programmatically as well.
It works on sleeping and running tasks as well.
Also, move up PROC_BLOCK_SIZE a bit so that proc_pid_stack() can use it.
[ mingo@...e.hu: small cleanups, comments ]
Signed-off-by: Ken Chen <kenchen@...gle.com>
Acked-by: Alexey Dobriyan <adobriyan@...il.com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
Documentation/filesystems/proc.txt | 1 +
fs/proc/base.c | 52 ++++++++++++++++++++++++++++++++++-
2 files changed, 51 insertions(+), 2 deletions(-)
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index bcceb99..11f5b75 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -139,6 +139,7 @@ Table 1-1: Process specific entries in /proc
statm Process memory status information
status Process status in human readable form
wchan If CONFIG_KALLSYMS is set, a pre-decoded wchan
+ stack Report full stack trace, enable via CONFIG_STACKTRACE
smaps Extension based on maps, the rss size for each mapped file
..............................................................................
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 486cf3f..805e514 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -65,6 +65,7 @@
#include <linux/mm.h>
#include <linux/rcupdate.h>
#include <linux/kallsyms.h>
+#include <linux/stacktrace.h>
#include <linux/resource.h>
#include <linux/module.h>
#include <linux/mount.h>
@@ -130,6 +131,12 @@ struct pid_entry {
{ .proc_show = &proc_##OTYPE } )
/*
+ * buffer size used for proc read. See proc_info_read().
+ * 4K page size but our output routines use some slack for overruns
+ */
+#define PROC_BLOCK_SIZE (3*1024)
+
+/*
* Count the number of hardlinks for the pid_entry table, excluding the .
* and .. links.
*/
@@ -340,6 +347,46 @@ static int proc_pid_wchan(struct task_struct *task, char *buffer)
}
#endif /* CONFIG_KALLSYMS */
+#ifdef CONFIG_STACKTRACE
+
+#define MAX_STACK_TRACE_DEPTH 64
+
+static int proc_pid_stack(struct task_struct *task, char *buffer)
+{
+ struct stack_trace trace;
+ unsigned long *entries;
+ int i, len = 0;
+
+ entries = kmalloc(sizeof(*entries)*MAX_STACK_TRACE_DEPTH, GFP_KERNEL);
+ if (!entries)
+ return -ENOMEM;
+
+ trace.nr_entries = 0;
+ trace.max_entries = MAX_STACK_TRACE_DEPTH;
+ trace.entries = entries;
+ trace.skip = 0;
+
+ /*
+ * Protect against the task exiting (and deallocating its
+ * stack, etc.) while we save its backtrace:
+ */
+ read_lock(&tasklist_lock);
+ save_stack_trace_tsk(task, &trace);
+ read_unlock(&tasklist_lock);
+
+ for (i = 0; i < trace.nr_entries; i++) {
+ len += snprintf(buffer + len, PROC_BLOCK_SIZE - len,
+ "[<%p>] %pS\n",
+ (void *)entries[i], (void *)entries[i]);
+ if (!len)
+ break;
+ }
+ kfree(entries);
+
+ return len;
+}
+#endif
+
#ifdef CONFIG_SCHEDSTATS
/*
* Provides /proc/PID/schedstat
@@ -688,8 +735,6 @@ static const struct file_operations proc_mountstats_operations = {
.release = mounts_release,
};
-#define PROC_BLOCK_SIZE (3*1024) /* 4K page size but our output routines use some slack for overruns */
-
static ssize_t proc_info_read(struct file * file, char __user * buf,
size_t count, loff_t *ppos)
{
@@ -2491,6 +2536,9 @@ static const struct pid_entry tgid_base_stuff[] = {
#ifdef CONFIG_KALLSYMS
INF("wchan", S_IRUGO, pid_wchan),
#endif
+#ifdef CONFIG_STACKTRACE
+ INF("stack", S_IRUSR, pid_stack),
+#endif
#ifdef CONFIG_SCHEDSTATS
INF("schedstat", S_IRUGO, pid_schedstat),
#endif
--
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