linux-kernel - Re: [patch] add /proc/pid/stack to dump task's stack trace

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Message-ID: <20081108121054.GG8354@elte.hu>
Date:	Sat, 8 Nov 2008 13:10:54 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Ken Chen <kenchen@...gle.com>
Cc:	Alexey Dobriyan <adobriyan@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	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


* Ken Chen <kenchen@...gle.com> wrote:

> On Fri, Nov 7, 2008 at 12:32 AM, Ingo Molnar <mingo@...e.hu> wrote:
> > oh well - Ken, could you please switch it to seqfiles?
> 
> On Fri, Nov 7, 2008 at 12:49 AM, Alexey Dobriyan wrote:
> > Or you can do all of this in ->show(), without start/next/stop:
> >
> >        for (i = 0; i < N; i++)
> >                seq_printf(m, "[<%p>] %pS\n", x, x);
> 
> Here is a patch convert to seq_file using proc_single_show() helper. 
> I don't see it to be any superior than what was before using 
> snprintf().  seq_read also allocate one page for printf buffer, so 
> functionally it is the same (perhaps a little bit better because it 
> can use the whole page, compare to PROC_BLOCK_SIZE currently).  
> Ingo, it's your call whether to merge this patch or not.
> 
> I also agree that using full blown seqfile start/show/stop won't add 
> value because most valuable stack at the top are already printed.

Well, it removes 2 lines of code and makes the iteration slightly more 
resilient (as there's no 'ret' value to be maintained anymore), so 
i've applied your patch to tip/core/stacktrace - thanks Ken! (see the 
commit below)

Sidenote: it would still be nice if the procfs folks converted the 
old-style code there to the new seqfile APIs, before requiring 
everyone _else_ to follow those guidelines?

	Ingo

----------------->
>From 35f0b5fd7fab907a1119eaa614d9b24e5e225755 Mon Sep 17 00:00:00 2001
From: Ken Chen <kenchen@...gle.com>
Date: Fri, 7 Nov 2008 10:38:04 -0800
Subject: [PATCH] stacktrace: convert /proc/<pid>/stack to seqfiles

Here is a patch convert to seq_file using proc_single_show() helper.

Signed-off-by: Ken Chen <kenchen@...gle.com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 fs/proc/base.c |   16 +++++++---------
 1 files changed, 7 insertions(+), 9 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 805e514..6d294a4 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -351,11 +351,12 @@ static int proc_pid_wchan(struct task_struct *task, char *buffer)
 
 #define MAX_STACK_TRACE_DEPTH	64
 
-static int proc_pid_stack(struct task_struct *task, char *buffer)
+static int proc_pid_stack(struct seq_file *m, struct pid_namespace *ns,
+			  struct pid *pid, struct task_struct *task)
 {
 	struct stack_trace trace;
 	unsigned long *entries;
-	int i, len = 0;
+	int i;
 
 	entries = kmalloc(sizeof(*entries)*MAX_STACK_TRACE_DEPTH, GFP_KERNEL);
 	if (!entries)
@@ -375,15 +376,12 @@ static int proc_pid_stack(struct task_struct *task, char *buffer)
 	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;
+		seq_printf(m, "[<%p>] %pS\n",
+			   (void *)entries[i], (void *)entries[i]);
 	}
 	kfree(entries);
 
-	return len;
+	return 0;
 }
 #endif
 
@@ -2537,7 +2535,7 @@ static const struct pid_entry tgid_base_stuff[] = {
 	INF("wchan",      S_IRUGO, pid_wchan),
 #endif
 #ifdef CONFIG_STACKTRACE
-	INF("stack",      S_IRUSR, pid_stack),
+	ONE("stack",      S_IRUSR, pid_stack),
 #endif
 #ifdef CONFIG_SCHEDSTATS
 	INF("schedstat",  S_IRUGO, pid_schedstat),
--
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