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Date: Wed, 30 Apr 2014 09:55:32 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Jiri Slaby <jslaby@...e.cz>
Cc: linux-kernel@...r.kernel.org, jirislaby@...il.com,
Vojtech Pavlik <vojtech@...e.cz>, Michael Matz <matz@...e.de>,
Jiri Kosina <jkosina@...e.cz>,
Steven Rostedt <rostedt@...dmis.org>,
Frederic Weisbecker <fweisbec@...il.com>,
Ingo Molnar <mingo@...hat.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Theodore Ts'o" <tytso@....edu>,
Dipankar Sarma <dipankar@...ibm.com>, Tejun Heo <tj@...nel.org>
Subject: Re: [RFC 09/16] kgr: mark task_safe in some kthreads
On Wed, Apr 30, 2014 at 04:30:42PM +0200, Jiri Slaby wrote:
> Some threads do not use kthread_should_stop. Before we enable a
> kthread support in kgr, we must make sure all those mark themselves
> safe explicitly.
Would it make sense to bury kgr_task_safe() in wait_event_interruptible()
and friends? The kgr_task_safe() implementation looks pretty lightweight,
so it should not be a performance problem.
One reason might this might be a bad idea is that there are calls to
wait_event_interruptible() all over the place, which might therefore
constrain where grafting could be safely done. That would be fair enough,
but does that also imply new constraints on where kthread_should_stop()
can be invoked? Any new constraints might not be a big deal given that
a very large fraction of the kthreads (and maybe all of them) invoke
kthread_should_stop() from their top-level function, but would be good
to call out.
So, what is the story?
Thanx, Paul
> Signed-off-by: Jiri Slaby <jslaby@...e.cz>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: "Theodore Ts'o" <tytso@....edu>
> Cc: Dipankar Sarma <dipankar@...ibm.com>
> Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> Cc: Tejun Heo <tj@...nel.org>
> ---
> drivers/base/devtmpfs.c | 1 +
> fs/jbd2/journal.c | 2 ++
> fs/notify/mark.c | 5 ++++-
> kernel/hung_task.c | 5 ++++-
> kernel/kthread.c | 3 +++
> kernel/rcu/tree.c | 6 ++++--
> kernel/rcu/tree_plugin.h | 9 +++++++--
> kernel/workqueue.c | 1 +
> 8 files changed, 26 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/base/devtmpfs.c b/drivers/base/devtmpfs.c
> index 25798db14553..c7d52d1b8c9c 100644
> --- a/drivers/base/devtmpfs.c
> +++ b/drivers/base/devtmpfs.c
> @@ -387,6 +387,7 @@ static int devtmpfsd(void *p)
> sys_chroot(".");
> complete(&setup_done);
> while (1) {
> + kgr_task_safe(current);
> spin_lock(&req_lock);
> while (requests) {
> struct req *req = requests;
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index 67b8e303946c..1b9c4c2e014a 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -43,6 +43,7 @@
> #include <linux/backing-dev.h>
> #include <linux/bitops.h>
> #include <linux/ratelimit.h>
> +#include <linux/sched.h>
>
> #define CREATE_TRACE_POINTS
> #include <trace/events/jbd2.h>
> @@ -260,6 +261,7 @@ loop:
> write_lock(&journal->j_state_lock);
> }
> finish_wait(&journal->j_wait_commit, &wait);
> + kgr_task_safe(current);
> }
>
> jbd_debug(1, "kjournald2 wakes\n");
> diff --git a/fs/notify/mark.c b/fs/notify/mark.c
> index 923fe4a5f503..a74b6175e645 100644
> --- a/fs/notify/mark.c
> +++ b/fs/notify/mark.c
> @@ -82,6 +82,7 @@
> #include <linux/kthread.h>
> #include <linux/module.h>
> #include <linux/mutex.h>
> +#include <linux/sched.h>
> #include <linux/slab.h>
> #include <linux/spinlock.h>
> #include <linux/srcu.h>
> @@ -355,7 +356,9 @@ static int fsnotify_mark_destroy(void *ignored)
> fsnotify_put_mark(mark);
> }
>
> - wait_event_interruptible(destroy_waitq, !list_empty(&destroy_list));
> + wait_event_interruptible(destroy_waitq, ({
> + kgr_task_safe(current);
> + !list_empty(&destroy_list); }));
> }
>
> return 0;
> diff --git a/kernel/hung_task.c b/kernel/hung_task.c
> index 06bb1417b063..b5f85bff2509 100644
> --- a/kernel/hung_task.c
> +++ b/kernel/hung_task.c
> @@ -14,6 +14,7 @@
> #include <linux/kthread.h>
> #include <linux/lockdep.h>
> #include <linux/export.h>
> +#include <linux/sched.h>
> #include <linux/sysctl.h>
> #include <linux/utsname.h>
> #include <trace/events/sched.h>
> @@ -227,8 +228,10 @@ static int watchdog(void *dummy)
> for ( ; ; ) {
> unsigned long timeout = sysctl_hung_task_timeout_secs;
>
> - while (schedule_timeout_interruptible(timeout_jiffies(timeout)))
> + while (schedule_timeout_interruptible(timeout_jiffies(timeout))) {
> + kgr_task_safe(current);
> timeout = sysctl_hung_task_timeout_secs;
> + }
>
> if (atomic_xchg(&reset_hung_task, 0))
> continue;
> diff --git a/kernel/kthread.c b/kernel/kthread.c
> index 9a130ec06f7a..08b979dad619 100644
> --- a/kernel/kthread.c
> +++ b/kernel/kthread.c
> @@ -78,6 +78,8 @@ static struct kthread *to_live_kthread(struct task_struct *k)
> */
> bool kthread_should_stop(void)
> {
> + kgr_task_safe(current);
> +
> return test_bit(KTHREAD_SHOULD_STOP, &to_kthread(current)->flags);
> }
> EXPORT_SYMBOL(kthread_should_stop);
> @@ -497,6 +499,7 @@ int kthreadd(void *unused)
> if (list_empty(&kthread_create_list))
> schedule();
> __set_current_state(TASK_RUNNING);
> + kgr_task_safe(current);
>
> spin_lock(&kthread_create_lock);
> while (!list_empty(&kthread_create_list)) {
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 0c47e300210a..5dddedacfc06 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -1593,9 +1593,10 @@ static int __noreturn rcu_gp_kthread(void *arg)
> trace_rcu_grace_period(rsp->name,
> ACCESS_ONCE(rsp->gpnum),
> TPS("reqwait"));
> - wait_event_interruptible(rsp->gp_wq,
> + wait_event_interruptible(rsp->gp_wq, ({
> + kgr_task_safe(current);
> ACCESS_ONCE(rsp->gp_flags) &
> - RCU_GP_FLAG_INIT);
> + RCU_GP_FLAG_INIT; }));
> /* Locking provides needed memory barrier. */
> if (rcu_gp_init(rsp))
> break;
> @@ -1626,6 +1627,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
> (!ACCESS_ONCE(rnp->qsmask) &&
> !rcu_preempt_blocked_readers_cgp(rnp)),
> j);
> + kgr_task_safe(current);
> /* Locking provides needed memory barriers. */
> /* If grace period done, leave loop. */
> if (!ACCESS_ONCE(rnp->qsmask) &&
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 962d1d589929..8b383003b228 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -27,6 +27,7 @@
> #include <linux/delay.h>
> #include <linux/gfp.h>
> #include <linux/oom.h>
> +#include <linux/sched.h>
> #include <linux/smpboot.h>
> #include "../time/tick-internal.h"
>
> @@ -1273,7 +1274,8 @@ static int rcu_boost_kthread(void *arg)
> for (;;) {
> rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
> trace_rcu_utilization(TPS("End boost kthread@..._wait"));
> - rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
> + rcu_wait(({ kgr_task_safe(current);
> + rnp->boost_tasks || rnp->exp_tasks; }));
> trace_rcu_utilization(TPS("Start boost kthread@..._wait"));
> rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
> more2boost = rcu_boost(rnp);
> @@ -2283,11 +2285,14 @@ static int rcu_nocb_kthread(void *arg)
>
> /* Each pass through this loop invokes one batch of callbacks */
> for (;;) {
> + kgr_task_safe(current);
> /* If not polling, wait for next batch of callbacks. */
> if (!rcu_nocb_poll) {
> trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
> TPS("Sleep"));
> - wait_event_interruptible(rdp->nocb_wq, rdp->nocb_head);
> + wait_event_interruptible(rdp->nocb_wq, ({
> + kgr_task_safe(current);
> + rdp->nocb_head; }));
> /* Memory barrier provide by xchg() below. */
> } else if (firsttime) {
> firsttime = 0;
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 0ee63af30bd1..4b89f1dc0dd8 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -2369,6 +2369,7 @@ sleep:
> __set_current_state(TASK_INTERRUPTIBLE);
> spin_unlock_irq(&pool->lock);
> schedule();
> + kgr_task_safe(current);
> goto woke_up;
> }
>
> --
> 1.9.2
>
--
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