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Date:   Sun,  9 Aug 2020 19:06:15 +0000
From:   Dmitry Monakhov <dmtrmonakhov@...dex-team.ru>
To:     linux-kernel@...r.kernel.org
Cc:     koct9i@...il.com, Dmitry Monakhov <dmtrmonakhov@...dex-team.ru>
Subject: [PATCH] lib/test_lockup.c: add parameters for cond_resched inside loop

call_cond_resched_before=Y  call cond_resched with resource before wait
call_cond_resched_after=Y   call cond_resched with resource after wait
measure_cond_resched=Y      measure maximum cond_resched time inside loop

This simulate situation where process call cond_resched() with lock held.

Example demonstrate priority inversion issue with epbf-program, where
low priority task sheduled out while holding cgroup_mutex for a long
periods of time which blocks others programs with high priority.

CGROUP_MUTEX=$(gawk '$3 == "cgroup_mutex" {print "0x"$1}' /proc/kallsyms)
# Emulate ebpf-application load which can hung inside cgroup_bpf_attach()
nice -20 modprobe lib/test_lockup.ko \
      time_nsecs=1000 cooldown_nsecs=100000 iterations=100000 \
      lock_mutex_ptr=$CGROUP_MUTEX \
      measure_lock_wait=Y call_cond_resched_after=Y &

stress-ng -c $(nproc) --timeout 10s&
time mkdir /sys/fs/cgroup/blkio/a

Signed-off-by: Dmitry Monakhov <dmtrmonakhov@...dex-team.ru>
---
 lib/test_lockup.c | 44 +++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 43 insertions(+), 1 deletion(-)

diff --git a/lib/test_lockup.c b/lib/test_lockup.c
index 0f81252..3e05d6e 100644
--- a/lib/test_lockup.c
+++ b/lib/test_lockup.c
@@ -77,6 +77,18 @@ static bool call_cond_resched;
 module_param(call_cond_resched, bool, 0600);
 MODULE_PARM_DESC(call_cond_resched, "call cond_resched() between iterations");
 
+static bool call_cond_resched_before;
+module_param(call_cond_resched_before, bool, 0600);
+MODULE_PARM_DESC(call_cond_resched_before, "call cond_resched() before wait");
+
+static bool call_cond_resched_after;
+module_param(call_cond_resched_after, bool, 0600);
+MODULE_PARM_DESC(call_cond_resched_after, "call cond_resched() after wait");
+
+static bool measure_cond_resched;
+module_param(measure_cond_resched, bool, 0400);
+MODULE_PARM_DESC(measure_cond_resched, "measure cond_resched time");
+
 static bool measure_lock_wait;
 module_param(measure_lock_wait, bool, 0400);
 MODULE_PARM_DESC(measure_lock_wait, "measure lock wait time");
@@ -162,6 +174,7 @@ MODULE_PARM_DESC(lock_sb_umount, "lock file -> sb -> s_umount");
 static atomic_t alloc_pages_failed = ATOMIC_INIT(0);
 
 static atomic64_t max_lock_wait = ATOMIC64_INIT(0);
+static atomic64_t max_cond_resched = ATOMIC64_INIT(0);
 
 static struct task_struct *main_task;
 static int master_cpu;
@@ -346,6 +359,22 @@ static void test_wait(unsigned int secs, unsigned int nsecs)
 	}
 }
 
+static void test_cond_resched(void)
+{
+	s64 cur, old_max;
+	s64 start = local_clock();
+
+	cond_resched();
+
+	cur  = local_clock() - start;
+	old_max = atomic64_read(&max_cond_resched);
+	do {
+		if (cur < old_max)
+			break;
+		old_max = atomic64_cmpxchg(&max_cond_resched, old_max, cur);
+	} while (old_max != cur);
+}
+
 static void test_lockup(bool master)
 {
 	u64 lockup_start = local_clock();
@@ -363,8 +392,14 @@ static void test_lockup(bool master)
 		if (iowait)
 			current->in_iowait = 1;
 
+		if (call_cond_resched_before)
+			test_cond_resched();
+
 		test_wait(time_secs, time_nsecs);
 
+		if (call_cond_resched_after)
+			test_cond_resched();
+
 		if (iowait)
 			current->in_iowait = 0;
 
@@ -497,6 +532,7 @@ static int __init test_lockup_init(void)
 
 	if ((wait_state != TASK_RUNNING ||
 	     (call_cond_resched && !reacquire_locks) ||
+	     call_cond_resched_before || call_cond_resched_after ||
 	     (alloc_pages_nr && gfpflags_allow_blocking(alloc_pages_gfp))) &&
 	    (test_disable_irq || disable_softirq || disable_preempt ||
 	     lock_rcu || lock_spinlock_ptr || lock_rwlock_ptr)) {
@@ -532,7 +568,7 @@ static int __init test_lockup_init(void)
 	if (test_lock_sb_umount && test_inode)
 		lock_rwsem_ptr = (unsigned long)&test_inode->i_sb->s_umount;
 
-	pr_notice("START pid=%d time=%u +%u ns cooldown=%u +%u ns iterations=%u state=%s %s%s%s%s%s%s%s%s%s%s%s\n",
+	pr_notice("START pid=%d time=%u +%u ns cooldown=%u +%u ns iterations=%u state=%s %s%s%s%s%s%s%s%s%s%s%s%s%s\n",
 		  main_task->pid, time_secs, time_nsecs,
 		  cooldown_secs, cooldown_nsecs, iterations, state,
 		  all_cpus ? "all_cpus " : "",
@@ -545,6 +581,8 @@ static int __init test_lockup_init(void)
 		  touch_softlockup ? "touch_softlockup " : "",
 		  touch_hardlockup ? "touch_hardlockup " : "",
 		  call_cond_resched ? "call_cond_resched " : "",
+		  call_cond_resched_before ? "call_cond_resched_before " : "",
+		  call_cond_resched_after ? "call_cond_resched_after " : "",
 		  reacquire_locks ? "reacquire_locks " : "");
 
 	if (alloc_pages_nr)
@@ -578,6 +616,10 @@ static int __init test_lockup_init(void)
 		pr_notice("Maximum lock wait: %lld ns\n",
 			  atomic64_read(&max_lock_wait));
 
+	if (measure_cond_resched)
+		pr_notice("Maximum cond resched time: %lld ns\n",
+			  atomic64_read(&max_cond_resched));
+
 	if (alloc_pages_nr)
 		pr_notice("Page allocation failed %u times\n",
 			  atomic_read(&alloc_pages_failed));
-- 
2.7.4

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