linux-kernel - [RFC] proc: get_wchan() stack unwind only makes sense for sleeping/non-self tasks

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Date:   Thu,  5 Nov 2020 15:11:32 -0800
From:   Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:     Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Alexey Gladkov <gladkov.alexey@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michel Lespinasse <walken@...gle.com>,
        Andrei Vagin <avagin@...il.com>,
        Bernd Edlinger <bernd.edlinger@...mail.de>,
        John Johansen <john.johansen@...onical.com>,
        Oleg Nesterov <oleg@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-snps-arc@...ts.infradead.org,
        Vineet Gupta <Vineet.Gupta1@...opsys.com>
Subject: [RFC] proc: get_wchan() stack unwind only makes sense for sleeping/non-self tasks

Most architectures currently check this in their get_wchan() implementation
(ARC doesn't hence this patch). However doing this in core code shows
the semantics better so move the check one level up (eventually remove
the boiler-plate code from arches)

Signed-off-by: Vineet Gupta <vgupta@...opsys.com>

 #	tools/perf/arch/arc/util/
---
 fs/proc/array.c | 4 +++-
 fs/proc/base.c  | 6 ++++--
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 65ec2029fa80..081fade5a361 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -519,8 +519,10 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
 		unlock_task_sighand(task, &flags);
 	}
 
-	if (permitted && (!whole || num_threads < 2))
+	if (task != current && task->state != TASK_RUNNING &&
+	    permitted && (!whole || num_threads < 2))
 		wchan = get_wchan(task);
+
 	if (!whole) {
 		min_flt = task->min_flt;
 		maj_flt = task->maj_flt;
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 0f707003dda5..abd7ec6324c5 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -385,13 +385,15 @@ static const struct file_operations proc_pid_cmdline_ops = {
 static int proc_pid_wchan(struct seq_file *m, struct pid_namespace *ns,
 			  struct pid *pid, struct task_struct *task)
 {
-	unsigned long wchan;
+	unsigned long wchan = 0;
 	char symname[KSYM_NAME_LEN];
 
 	if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS))
 		goto print0;
 
-	wchan = get_wchan(task);
+	if (task != current && task->state != TASK_RUNNING)
+		wchan = get_wchan(task);
+
 	if (wchan && !lookup_symbol_name(wchan, symname)) {
 		seq_puts(m, symname);
 		return 0;
-- 
2.25.1