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Message-ID: <20201105154653.GB2656962@google.com>
Date: Thu, 5 Nov 2020 10:46:53 -0500
From: Joel Fernandes <joel@...lfernandes.org>
To: chris hyser <chris.hyser@...cle.com>
Cc: Nishanth Aravamudan <naravamudan@...italocean.com>,
Julien Desfossez <jdesfossez@...italocean.com>,
Peter Zijlstra <peterz@...radead.org>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Vineeth Pillai <viremana@...ux.microsoft.com>,
Aaron Lu <aaron.lwe@...il.com>,
Aubrey Li <aubrey.intel@...il.com>, tglx@...utronix.de,
linux-kernel@...r.kernel.org, mingo@...nel.org,
torvalds@...ux-foundation.org, fweisbec@...il.com,
keescook@...omium.org, kerrnel@...gle.com,
Phil Auld <pauld@...hat.com>,
Valentin Schneider <valentin.schneider@....com>,
Mel Gorman <mgorman@...hsingularity.net>,
Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
Paolo Bonzini <pbonzini@...hat.com>, vineeth@...byteword.org,
Chen Yu <yu.c.chen@...el.com>,
Christian Brauner <christian.brauner@...ntu.com>,
Agata Gruza <agata.gruza@...el.com>,
Antonio Gomez Iglesias <antonio.gomez.iglesias@...el.com>,
graf@...zon.com, konrad.wilk@...cle.com, dfaggioli@...e.com,
pjt@...gle.com, rostedt@...dmis.org, derkling@...gle.com,
benbjiang@...cent.com,
Alexandre Chartre <alexandre.chartre@...cle.com>,
James.Bottomley@...senpartnership.com, OWeisse@...ch.edu,
Dhaval Giani <dhaval.giani@...cle.com>,
Junaid Shahid <junaids@...gle.com>, jsbarnes@...gle.com,
Aubrey Li <aubrey.li@...ux.intel.com>,
"Paul E. McKenney" <paulmck@...nel.org>,
Tim Chen <tim.c.chen@...el.com>
Subject: Re: [PATCH v8 -tip 20/26] sched: Release references to the per-task
cookie on exit
On Wed, Nov 04, 2020 at 04:50:42PM -0500, chris hyser wrote:
> On 10/19/20 9:43 PM, Joel Fernandes (Google) wrote:
> > During exit, we have to free the references to a cookie that might be shared by
> > many tasks. This commit therefore ensures when the task_struct is released, any
> > references to cookies that it holds are also released.
> >
> > Tested-by: Julien Desfossez <jdesfossez@...italocean.com>
> > Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> > ---
> > include/linux/sched.h | 2 ++
> > kernel/fork.c | 1 +
> > kernel/sched/core.c | 8 ++++++++
> > 3 files changed, 11 insertions(+)
> >
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index 4cb76575afa8..eabd96beff92 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -2079,12 +2079,14 @@ void sched_core_unsafe_exit(void);
> > bool sched_core_wait_till_safe(unsigned long ti_check);
> > bool sched_core_kernel_protected(void);
> > int sched_core_share_pid(pid_t pid);
> > +void sched_tsk_free(struct task_struct *tsk);
> > #else
> > #define sched_core_unsafe_enter(ignore) do { } while (0)
> > #define sched_core_unsafe_exit(ignore) do { } while (0)
> > #define sched_core_wait_till_safe(ignore) do { } while (0)
> > #define sched_core_kernel_protected(ignore) do { } while (0)
> > #define sched_core_share_pid(pid_t pid) do { } while (0)
> > +#define sched_tsk_free(tsk) do { } while (0)
> > #endif
> > #endif
> > diff --git a/kernel/fork.c b/kernel/fork.c
> > index b9c289d0f4ef..a39248a02fdd 100644
> > --- a/kernel/fork.c
> > +++ b/kernel/fork.c
> > @@ -736,6 +736,7 @@ void __put_task_struct(struct task_struct *tsk)
> > exit_creds(tsk);
> > delayacct_tsk_free(tsk);
> > put_signal_struct(tsk->signal);
> > + sched_tsk_free(tsk);
> > if (!profile_handoff_task(tsk))
> > free_task(tsk);
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 42aa811eab14..61e1dcf11000 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -9631,6 +9631,14 @@ static int cpu_core_tag_color_write_u64(struct cgroup_subsys_state *css,
> > return 0;
> > }
> > +
> > +void sched_tsk_free(struct task_struct *tsk)
> > +{
> > + if (!tsk->core_task_cookie)
> > + return;
> > + sched_core_put_task_cookie(tsk->core_task_cookie);
> > + sched_core_put();
>
>
> sched_tsk_free() can be called under softirq. sched_core_put() is riddled with things that may want to sleep.
Right, that breaks. Can you try the diff I attached below and see if it does
not crash now?
> I tried a number of things like replacing the mutexes in put/get with spin_lock_bh() and just kept finding things like:
>
>
> [root@...ser-vm5 bin]# [ 1123.516209] BUG: sleeping function called from invalid context at include/linux/percpu-rwsem.h:49
Indeed, stop machine cannot be called from an atomic context, which is what
spin_lock_bh gives you.
---8<-----------------------
diff --git a/kernel/sched/coretag.c b/kernel/sched/coretag.c
index 6c008e5471d7..9967f37c5df0 100644
--- a/kernel/sched/coretag.c
+++ b/kernel/sched/coretag.c
@@ -16,6 +16,7 @@
*/
struct sched_core_cookie {
refcount_t refcnt;
+ struct work_struct work; /* to free in WQ context. */;
};
static DEFINE_MUTEX(sched_core_tasks_mutex);
@@ -54,21 +55,24 @@ void sched_core_tag_requeue(struct task_struct *p, unsigned long cookie, bool gr
}
/* Per-task interface: Used by fork(2) and prctl(2). */
+static void sched_core_put_cookie_work(struct work_struct *ws);
+
static unsigned long sched_core_alloc_task_cookie(void)
{
- struct sched_core_cookie *ptr =
+ struct sched_core_cookie *ck =
kmalloc(sizeof(struct sched_core_cookie), GFP_KERNEL);
- if (!ptr)
+ if (!ck)
return 0;
- refcount_set(&ptr->refcnt, 1);
+ refcount_set(&ck->refcnt, 1);
+ INIT_WORK(&ck->work, sched_core_put_cookie_work);
/*
* NOTE: sched_core_put() is not done by put_task_cookie(). Instead, it
* is done after the stopper runs.
*/
sched_core_get();
- return (unsigned long)ptr;
+ return (unsigned long)ck;
}
static bool sched_core_get_task_cookie(unsigned long cookie)
@@ -91,6 +95,15 @@ static void sched_core_put_task_cookie(unsigned long cookie)
kfree(ptr);
}
+static void sched_core_put_cookie_work(struct work_struct *ws)
+{
+ struct sched_core_cookie *ck =
+ container_of(ws, struct sched_core_cookie, work);
+
+ sched_core_put_task_cookie((unsigned long)ck);
+ sched_core_put();
+}
+
struct sched_core_task_write_tag {
struct task_struct *tasks[2];
unsigned long cookies[2];
@@ -461,8 +474,11 @@ int cpu_core_tag_color_write_u64(struct cgroup_subsys_state *css,
void sched_tsk_free(struct task_struct *tsk)
{
+ struct sched_core_cookie *ck;
+
if (!tsk->core_task_cookie)
return;
- sched_core_put_task_cookie(tsk->core_task_cookie);
- sched_core_put();
+
+ ck = (struct sched_core_cookie *)tsk->core_task_cookie;
+ queue_work(system_wq, &ck->work);
}
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