Commit b88f5538 authored by Tetsuo Handa's avatar Tetsuo Handa Committed by Linus Torvalds
Browse files

profiling: remove profile=sleep support 



The kernel sleep profile is no longer working due to a recursive locking
bug introduced by commit 42a20f86 ("sched: Add wrapper for get_wchan()
to keep task blocked")

Booting with the 'profile=sleep' kernel command line option added or
executing

  # echo -n sleep > /sys/kernel/profiling

after boot causes the system to lock up.

Lockdep reports

  kthreadd/3 is trying to acquire lock:
  ffff93ac82e08d58 (&p->pi_lock){....}-{2:2}, at: get_wchan+0x32/0x70

  but task is already holding lock:
  ffff93ac82e08d58 (&p->pi_lock){....}-{2:2}, at: try_to_wake_up+0x53/0x370

with the call trace being

   lock_acquire+0xc8/0x2f0
   get_wchan+0x32/0x70
   __update_stats_enqueue_sleeper+0x151/0x430
   enqueue_entity+0x4b0/0x520
   enqueue_task_fair+0x92/0x6b0
   ttwu_do_activate+0x73/0x140
   try_to_wake_up+0x213/0x370
   swake_up_locked+0x20/0x50
   complete+0x2f/0x40
   kthread+0xfb/0x180

However, since nobody noticed this regression for more than two years,
let's remove 'profile=sleep' support based on the assumption that nobody
needs this functionality.

Fixes: 42a20f86 ("sched: Add wrapper for get_wchan() to keep task blocked")
Cc: stable@vger.kernel.org # v5.16+
Signed-off-by: default avatarTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent a5dbd76a

Documentation/admin-guide/kernel-parameters.txt

+1 −3
Original line number Diff line number Diff line
@@ -4798,11 +4798,9 @@ 


	profile=	[KNL] Enable kernel profiling via /proc/profile

			Format: [<profiletype>,]<number>

			Param: <profiletype>: "schedule", "sleep", or "kvm"

			Param: <profiletype>: "schedule" or "kvm"

				[defaults to kernel profiling]

			Param: "schedule" - profile schedule points.

			Param: "sleep" - profile D-state sleeping (millisecs).

				Requires CONFIG_SCHEDSTATS

			Param: "kvm" - profile VM exits.

			Param: <number> - step/bucket size as a power of 2 for

				statistical time based profiling.

include/linux/profile.h

+0 −1
Original line number Diff line number Diff line
@@ -10,7 +10,6 @@ 


#define CPU_PROFILING	1

#define SCHED_PROFILING	2

#define SLEEP_PROFILING	3

#define KVM_PROFILING	4



struct proc_dir_entry;

kernel/profile.c

+1 −10
Original line number Diff line number Diff line
@@ -50,20 +50,11 @@ EXPORT_SYMBOL_GPL(prof_on); 
int profile_setup(char *str)

{

	static const char schedstr[] = "schedule";

	static const char sleepstr[] = "sleep";

	static const char kvmstr[] = "kvm";

	const char *select = NULL;

	int par;



	if (!strncmp(str, sleepstr, strlen(sleepstr))) {

#ifdef CONFIG_SCHEDSTATS

		force_schedstat_enabled();

		prof_on = SLEEP_PROFILING;

		select = sleepstr;

#else

		pr_warn("kernel sleep profiling requires CONFIG_SCHEDSTATS\n");

#endif /* CONFIG_SCHEDSTATS */

	} else if (!strncmp(str, schedstr, strlen(schedstr))) {

	if (!strncmp(str, schedstr, strlen(schedstr))) {

		prof_on = SCHED_PROFILING;

		select = schedstr;

	} else if (!strncmp(str, kvmstr, strlen(kvmstr))) {

kernel/sched/stats.c

+0 −10
Original line number Diff line number Diff line
@@ -92,16 +92,6 @@ void __update_stats_enqueue_sleeper(struct rq *rq, struct task_struct *p, 


			trace_sched_stat_blocked(p, delta);



			/*

			 * Blocking time is in units of nanosecs, so shift by

			 * 20 to get a milliseconds-range estimation of the

			 * amount of time that the task spent sleeping:

			 */

			if (unlikely(prof_on == SLEEP_PROFILING)) {

				profile_hits(SLEEP_PROFILING,

					     (void *)get_wchan(p),

					     delta >> 20);

			}

			account_scheduler_latency(p, delta >> 10, 0);

		}

	}