Messages in this thread Patch in this message | | | Date | Wed, 30 Aug 2017 17:53:53 +0000 (UTC) | From | Mathieu Desnoyers <> | Subject | Re: [RFC PATCH 2/2] membarrier: provide register sync core cmd |
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----- On Aug 28, 2017, at 1:49 PM, Paul E. McKenney paulmck@linux.vnet.ibm.com wrote:
> On Sun, Aug 27, 2017 at 09:39:54PM +0000, Mathieu Desnoyers wrote: >> ----- On Aug 27, 2017, at 2:00 PM, Paul E. McKenney paulmck@linux.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@linux.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. > > And it looks like we also need a sync_core() on every CPU family other > than x86, which already has one. Do we want to make this capability > depend on an ARCH_ kconfig option, or should we just bit the bullet and > implement sync_core() everywhere? > > (I had to drop this commit due to downstream complaints. Left to myself, > I would take the ARCH_ approach, then add it back in, but please let me > know how you would like to proceed.)
I plan to go with the ARCH_ approach indeed.
Thanks,
Mathieu
> > Thanx, Paul > >> 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@efficios.com> >> >> >> CC: Peter Zijlstra <peterz@infradead.org> >> >> >> CC: Paul E. McKenney <paulmck@linux.vnet.ibm.com> >> >> >> CC: Boqun Feng <boqun.feng@gmail.com> >> >> >> CC: Andrew Hunter <ahh@google.com> >> >> >> CC: Maged Michael <maged.michael@gmail.com> >> >> >> CC: gromer@google.com >> >> >> CC: Avi Kivity <avi@scylladb.com> >> >> >> CC: Benjamin Herrenschmidt <benh@kernel.crashing.org> >> >> >> CC: Paul Mackerras <paulus@samba.org> >> >> >> CC: Michael Ellerman <mpe@ellerman.id.au> >> >> >> CC: Dave Watson <davejwatson@fb.com> >> >> >> CC: Andy Lutomirski <luto@kernel.org> >> >> >> CC: Will Deacon <will.deacon@arm.com> >> >> >> CC: Hans Boehm <hboehm@google.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
-- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
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