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Message-ID: <1573504622.16850.1503869994880.JavaMail.zimbra@efficios.com>
Date: Sun, 27 Aug 2017 21:39:54 +0000 (UTC)
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
linux-kernel <linux-kernel@...r.kernel.org>,
Boqun Feng <boqun.feng@...il.com>,
Andrew Hunter <ahh@...gle.com>,
maged michael <maged.michael@...il.com>,
gromer <gromer@...gle.com>, Avi Kivity <avi@...lladb.com>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Paul Mackerras <paulus@...ba.org>,
Michael Ellerman <mpe@...erman.id.au>,
Dave Watson <davejwatson@...com>,
Andy Lutomirski <luto@...nel.org>,
Will Deacon <will.deacon@....com>,
Hans Boehm <hboehm@...gle.com>
Subject: Re: [RFC PATCH 2/2] membarrier: provide register sync core cmd
----- On Aug 27, 2017, at 2:00 PM, Paul E. McKenney paulmck@...ux.vnet.ibm.com wrote:
> On Sun, Aug 27, 2017 at 08:52:58PM +0000, Mathieu Desnoyers wrote:
>> ----- On Aug 27, 2017, at 1:35 PM, Paul E. McKenney paulmck@...ux.vnet.ibm.com
>> wrote:
>>
>> > On Sun, Aug 27, 2017 at 12:54:04PM -0700, Mathieu Desnoyers wrote:
>> >> Add a new MEMBARRIER_CMD_REGISTER_SYNC_CORE command to the membarrier
>> >> system call. It allows processes to register their intent to have their
>> >> threads issue core serializing barriers in addition to memory barriers
>> >> whenever a membarrier command is performed.
>> >>
>> >> It is relevant for reclaim of JIT code, which requires to issue core
>> >> serializing barriers on all threads running on behalf of a process
>> >> after ensuring the old code is not visible anymore, before re-using
>> >> memory for new code.
>> >>
>> >> When a processes returns from a MEMBARRIER_CMD_REGISTER_SYNC_CORE
>> >> command, it is guaranteed that all following MEMBARRIER_CMD_SHARED and
>> >> MEMBARRIER_CMD_PRIVATE_EXPEDITED issue core serializing barriers, in
>> >> addition to the memory barriers, on all of its running threads.
>> >
>> > I have queued both of these for testing and review:
>> >
>> > git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git
>> > f54cf5123eb9 ("membarrier: Speed up single-threaded private cmd")
>> > 0d6eb99818da ("membarrier: Provide register sync core cmd")
>> >
>> > Could the people who asked for this please test it? The second commit
>> > is non-obvious enough to need some careful review and intensive testing
>> > before I can in good conscious pass it upstream.
>>
>> Thanks Paul!
>>
>> Can you pick up my v2 instead ? I added benchmarks in the changelog and
>> documented the new command in the membarrier public header. No changes
>> otherwise.
>
> It looks like 0day Test Robot also wants some additional header files.
> Could you please send me a v3 with its complaints addressed?
I sent a separate patch implementing sync_core() on xtensa. It should
be applied before this patch.
Hopefully we can get some testing from people with xtensa testing
environments.
Thanks,
Mathieu
>
> Thanx, Paul
>
>> Thanks,
>>
>> Mathieu
>>
>> >
>> > Thanx, Paul
>> >
>> >> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
>> >> CC: Peter Zijlstra <peterz@...radead.org>
>> >> CC: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
>> >> CC: Boqun Feng <boqun.feng@...il.com>
>> >> CC: Andrew Hunter <ahh@...gle.com>
>> >> CC: Maged Michael <maged.michael@...il.com>
>> >> CC: gromer@...gle.com
>> >> CC: Avi Kivity <avi@...lladb.com>
>> >> CC: Benjamin Herrenschmidt <benh@...nel.crashing.org>
>> >> CC: Paul Mackerras <paulus@...ba.org>
>> >> CC: Michael Ellerman <mpe@...erman.id.au>
>> >> CC: Dave Watson <davejwatson@...com>
>> >> CC: Andy Lutomirski <luto@...nel.org>
>> >> CC: Will Deacon <will.deacon@....com>
>> >> CC: Hans Boehm <hboehm@...gle.com>
>> >> ---
>> >> fs/exec.c | 1 +
>> >> include/linux/sched.h | 52 +++++++++++++++++++++++++++++++++++++++++
>> >> include/uapi/linux/membarrier.h | 1 +
>> >> kernel/fork.c | 2 ++
>> >> kernel/sched/core.c | 3 +++
>> >> kernel/sched/membarrier.c | 37 ++++++++++++++++++++++++++---
>> >> 6 files changed, 93 insertions(+), 3 deletions(-)
>> >>
>> >> diff --git a/fs/exec.c b/fs/exec.c
>> >> index 62175cbcc801..a4ab3253bac7 100644
>> >> --- a/fs/exec.c
>> >> +++ b/fs/exec.c
>> >> @@ -1794,6 +1794,7 @@ static int do_execveat_common(int fd, struct filename
>> >> *filename,
>> >> /* execve succeeded */
>> >> current->fs->in_exec = 0;
>> >> current->in_execve = 0;
>> >> + membarrier_execve(current);
>> >> acct_update_integrals(current);
>> >> task_numa_free(current);
>> >> free_bprm(bprm);
>> >> diff --git a/include/linux/sched.h b/include/linux/sched.h
>> >> index 8337e2db0bb2..b1ecdc4e8b84 100644
>> >> --- a/include/linux/sched.h
>> >> +++ b/include/linux/sched.h
>> >> @@ -1086,6 +1086,9 @@ struct task_struct {
>> >> /* Used by LSM modules for access restriction: */
>> >> void *security;
>> >> #endif
>> >> +#ifdef CONFIG_MEMBARRIER
>> >> + int membarrier_sync_core;
>> >> +#endif
>> >>
>> >> /*
>> >> * New fields for task_struct should be added above here, so that
>> >> @@ -1623,4 +1626,53 @@ extern long sched_getaffinity(pid_t pid, struct cpumask
>> >> *mask);
>> >> #define TASK_SIZE_OF(tsk) TASK_SIZE
>> >> #endif
>> >>
>> >> +#ifdef CONFIG_MEMBARRIER
>> >> +static inline void membarrier_fork(struct task_struct *t,
>> >> + unsigned long clone_flags)
>> >> +{
>> >> + /*
>> >> + * Coherence of membarrier_sync_core against thread fork is
>> >> + * protected by siglock. membarrier_fork is called with siglock
>> >> + * held.
>> >> + */
>> >> + t->membarrier_sync_core = current->membarrier_sync_core;
>> >> +}
>> >> +static inline void membarrier_execve(struct task_struct *t)
>> >> +{
>> >> + t->membarrier_sync_core = 0;
>> >> +}
>> >> +static inline void membarrier_sched_out(struct task_struct *t)
>> >> +{
>> >> + /*
>> >> + * Core serialization is performed before the memory barrier
>> >> + * preceding the store to rq->curr.
>> >> + */
>> >> + if (unlikely(READ_ONCE(t->membarrier_sync_core)))
>> >> + sync_core();
>> >> +}
>> >> +static inline void membarrier_sched_in(struct task_struct *t)
>> >> +{
>> >> + /*
>> >> + * Core serialization is performed after the memory barrier
>> >> + * following the store to rq->curr.
>> >> + */
>> >> + if (unlikely(READ_ONCE(t->membarrier_sync_core)))
>> >> + sync_core();
>> >> +}
>> >> +#else
>> >> +static inline void membarrier_fork(struct task_struct *t,
>> >> + unsigned long clone_flags)
>> >> +{
>> >> +}
>> >> +static inline void membarrier_execve(struct task_struct *t)
>> >> +{
>> >> +}
>> >> +static inline void membarrier_sched_out(struct task_struct *t)
>> >> +{
>> >> +}
>> >> +static inline void membarrier_sched_in(struct task_struct *t)
>> >> +{
>> >> +}
>> >> +#endif
>> >> +
>> >> #endif
>> >> diff --git a/include/uapi/linux/membarrier.h b/include/uapi/linux/membarrier.h
>> >> index 6d47b3249d8a..bc26fcf8fb7b 100644
>> >> --- a/include/uapi/linux/membarrier.h
>> >> +++ b/include/uapi/linux/membarrier.h
>> >> @@ -67,6 +67,7 @@ enum membarrier_cmd {
>> >> /* reserved for MEMBARRIER_CMD_SHARED_EXPEDITED (1 << 1) */
>> >> /* reserved for MEMBARRIER_CMD_PRIVATE (1 << 2) */
>> >> MEMBARRIER_CMD_PRIVATE_EXPEDITED = (1 << 3),
>> >> + MEMBARRIER_CMD_REGISTER_SYNC_CORE = (1 << 4),
>> >> };
>> >>
>> >> #endif /* _UAPI_LINUX_MEMBARRIER_H */
>> >> diff --git a/kernel/fork.c b/kernel/fork.c
>> >> index 17921b0390b4..713b3c932671 100644
>> >> --- a/kernel/fork.c
>> >> +++ b/kernel/fork.c
>> >> @@ -1840,6 +1840,8 @@ static __latent_entropy struct task_struct *copy_process(
>> >> */
>> >> copy_seccomp(p);
>> >>
>> >> + membarrier_fork(p, clone_flags);
>> >> +
>> >> /*
>> >> * Process group and session signals need to be delivered to just the
>> >> * parent before the fork or both the parent and the child after the
>> >> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> >> index 0e36d9960d91..3ca27d066950 100644
>> >> --- a/kernel/sched/core.c
>> >> +++ b/kernel/sched/core.c
>> >> @@ -3292,6 +3292,8 @@ static void __sched notrace __schedule(bool preempt)
>> >> local_irq_disable();
>> >> rcu_note_context_switch(preempt);
>> >>
>> >> + membarrier_sched_out(prev);
>> >> +
>> >> /*
>> >> * Make sure that signal_pending_state()->signal_pending() below
>> >> * can't be reordered with __set_current_state(TASK_INTERRUPTIBLE)
>> >> @@ -3364,6 +3366,7 @@ static void __sched notrace __schedule(bool preempt)
>> >>
>> >> /* Also unlocks the rq: */
>> >> rq = context_switch(rq, prev, next, &rf);
>> >> + membarrier_sched_in(next);
>> >> } else {
>> >> rq->clock_update_flags &= ~(RQCF_ACT_SKIP|RQCF_REQ_SKIP);
>> >> rq_unlock_irq(rq, &rf);
>> >> diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
>> >> index 7eec6914d2d2..f128caf64b49 100644
>> >> --- a/kernel/sched/membarrier.c
>> >> +++ b/kernel/sched/membarrier.c
>> >> @@ -25,12 +25,16 @@
>> >> * Bitmask made from a "or" of all commands within enum membarrier_cmd,
>> >> * except MEMBARRIER_CMD_QUERY.
>> >> */
>> >> -#define MEMBARRIER_CMD_BITMASK \
>> >> - (MEMBARRIER_CMD_SHARED | MEMBARRIER_CMD_PRIVATE_EXPEDITED)
>> >> +#define MEMBARRIER_CMD_BITMASK \
>> >> + (MEMBARRIER_CMD_SHARED \
>> >> + | MEMBARRIER_CMD_PRIVATE_EXPEDITED \
>> >> + | MEMBARRIER_CMD_REGISTER_SYNC_CORE)
>> >>
>> >> static void ipi_mb(void *info)
>> >> {
>> >> - smp_mb(); /* IPIs should be serializing but paranoid. */
>> >> + /* IPIs should be serializing but paranoid. */
>> >> + smp_mb();
>> >> + sync_core();
>> >> }
>> >>
>> >> static void membarrier_private_expedited(void)
>> >> @@ -96,6 +100,30 @@ static void membarrier_private_expedited(void)
>> >> smp_mb(); /* exit from system call is not a mb */
>> >> }
>> >>
>> >> +static void membarrier_register_sync_core(void)
>> >> +{
>> >> + struct task_struct *p = current, *t;
>> >> +
>> >> + if (get_nr_threads(p) == 1) {
>> >> + p->membarrier_sync_core = 1;
>> >> + return;
>> >> + }
>> >> +
>> >> + /*
>> >> + * Coherence of membarrier_sync_core against thread fork is
>> >> + * protected by siglock.
>> >> + */
>> >> + spin_lock(&p->sighand->siglock);
>> >> + for_each_thread(p, t)
>> >> + WRITE_ONCE(t->membarrier_sync_core, 1);
>> >> + spin_unlock(&p->sighand->siglock);
>> >> + /*
>> >> + * Ensure all future scheduler execution will observe the new
>> >> + * membarrier_sync_core state for this process.
>> >> + */
>> >> + synchronize_sched();
>> >> +}
>> >> +
>> >> /**
>> >> * sys_membarrier - issue memory barriers on a set of threads
>> >> * @cmd: Takes command values defined in enum membarrier_cmd.
>> >> @@ -146,6 +174,9 @@ SYSCALL_DEFINE2(membarrier, int, cmd, int, flags)
>> >> case MEMBARRIER_CMD_PRIVATE_EXPEDITED:
>> >> membarrier_private_expedited();
>> >> return 0;
>> >> + case MEMBARRIER_CMD_REGISTER_SYNC_CORE:
>> >> + membarrier_register_sync_core();
>> >> + return 0;
>> >> default:
>> >> return -EINVAL;
>> >> }
>> >> --
>> >> 2.11.0
>>
>> --
>> Mathieu Desnoyers
>> EfficiOS Inc.
>> http://www.efficios.com
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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