summaryrefslogtreecommitdiff
diff options
context:
space:
mode:
authorMathieu Desnoyers <mathieu.desnoyers@efficios.com>2018-01-29 15:20:11 -0500
committerIngo Molnar <mingo@kernel.org>2018-02-05 21:34:02 +0100
commit3ccfebedd8cf54e291c809c838d8ad5cc00f5688 (patch)
tree1366b6cb9a9b7af1fa8f4eb8fc252f897eaf1ba8
parent667ca1ec7c9eb7ac3b80590b6597151b4c2a750b (diff)
powerpc, membarrier: Skip memory barrier in switch_mm()
Allow PowerPC to skip the full memory barrier in switch_mm(), and only issue the barrier when scheduling into a task belonging to a process that has registered to use expedited private. Threads targeting the same VM but which belong to different thread groups is a tricky case. It has a few consequences: It turns out that we cannot rely on get_nr_threads(p) to count the number of threads using a VM. We can use (atomic_read(&mm->mm_users) == 1 && get_nr_threads(p) == 1) instead to skip the synchronize_sched() for cases where the VM only has a single user, and that user only has a single thread. It also turns out that we cannot use for_each_thread() to set thread flags in all threads using a VM, as it only iterates on the thread group. Therefore, test the membarrier state variable directly rather than relying on thread flags. This means membarrier_register_private_expedited() needs to set the MEMBARRIER_STATE_PRIVATE_EXPEDITED flag, issue synchronize_sched(), and only then set MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY which allows private expedited membarrier commands to succeed. membarrier_arch_switch_mm() now tests for the MEMBARRIER_STATE_PRIVATE_EXPEDITED flag. Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Acked-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Alan Stern <stern@rowland.harvard.edu> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Andrea Parri <parri.andrea@gmail.com> Cc: Andrew Hunter <ahh@google.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Avi Kivity <avi@scylladb.com> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Dave Watson <davejwatson@fb.com> Cc: David Sehr <sehr@google.com> Cc: Greg Hackmann <ghackmann@google.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Maged Michael <maged.michael@gmail.com> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Paul Mackerras <paulus@samba.org> Cc: Russell King <linux@armlinux.org.uk> Cc: Will Deacon <will.deacon@arm.com> Cc: linux-api@vger.kernel.org Cc: linux-arch@vger.kernel.org Cc: linuxppc-dev@lists.ozlabs.org Link: http://lkml.kernel.org/r/20180129202020.8515-3-mathieu.desnoyers@efficios.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
-rw-r--r--MAINTAINERS1
-rw-r--r--arch/powerpc/Kconfig1
-rw-r--r--arch/powerpc/include/asm/membarrier.h26
-rw-r--r--arch/powerpc/mm/mmu_context.c7
-rw-r--r--include/linux/sched/mm.h13
-rw-r--r--init/Kconfig3
-rw-r--r--kernel/sched/core.c10
-rw-r--r--kernel/sched/membarrier.c8
8 files changed, 58 insertions, 11 deletions
diff --git a/MAINTAINERS b/MAINTAINERS
index 217a8759e897..8e96d4e9677b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -8944,6 +8944,7 @@ L: linux-kernel@vger.kernel.org
S: Supported
F: kernel/sched/membarrier.c
F: include/uapi/linux/membarrier.h
+F: arch/powerpc/include/asm/membarrier.h
MEMORY MANAGEMENT
L: linux-mm@kvack.org
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 2ed525a44734..a2380de50878 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -140,6 +140,7 @@ config PPC
select ARCH_HAS_FORTIFY_SOURCE
select ARCH_HAS_GCOV_PROFILE_ALL
select ARCH_HAS_PMEM_API if PPC64
+ select ARCH_HAS_MEMBARRIER_CALLBACKS
select ARCH_HAS_SCALED_CPUTIME if VIRT_CPU_ACCOUNTING_NATIVE
select ARCH_HAS_SG_CHAIN
select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
diff --git a/arch/powerpc/include/asm/membarrier.h b/arch/powerpc/include/asm/membarrier.h
new file mode 100644
index 000000000000..98ff4f1fcf2b
--- /dev/null
+++ b/arch/powerpc/include/asm/membarrier.h
@@ -0,0 +1,26 @@
+#ifndef _ASM_POWERPC_MEMBARRIER_H
+#define _ASM_POWERPC_MEMBARRIER_H
+
+static inline void membarrier_arch_switch_mm(struct mm_struct *prev,
+ struct mm_struct *next,
+ struct task_struct *tsk)
+{
+ /*
+ * Only need the full barrier when switching between processes.
+ * Barrier when switching from kernel to userspace is not
+ * required here, given that it is implied by mmdrop(). Barrier
+ * when switching from userspace to kernel is not needed after
+ * store to rq->curr.
+ */
+ if (likely(!(atomic_read(&next->membarrier_state) &
+ MEMBARRIER_STATE_PRIVATE_EXPEDITED) || !prev))
+ return;
+
+ /*
+ * The membarrier system call requires a full memory barrier
+ * after storing to rq->curr, before going back to user-space.
+ */
+ smp_mb();
+}
+
+#endif /* _ASM_POWERPC_MEMBARRIER_H */
diff --git a/arch/powerpc/mm/mmu_context.c b/arch/powerpc/mm/mmu_context.c
index d60a62bf4fc7..0ab297c4cfad 100644
--- a/arch/powerpc/mm/mmu_context.c
+++ b/arch/powerpc/mm/mmu_context.c
@@ -12,6 +12,7 @@
#include <linux/mm.h>
#include <linux/cpu.h>
+#include <linux/sched/mm.h>
#include <asm/mmu_context.h>
@@ -58,6 +59,10 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
*
* On the read side the barrier is in pte_xchg(), which orders
* the store to the PTE vs the load of mm_cpumask.
+ *
+ * This full barrier is needed by membarrier when switching
+ * between processes after store to rq->curr, before user-space
+ * memory accesses.
*/
smp_mb();
@@ -80,6 +85,8 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
if (new_on_cpu)
radix_kvm_prefetch_workaround(next);
+ else
+ membarrier_arch_switch_mm(prev, next, tsk);
/*
* The actual HW switching method differs between the various
diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
index 3d49b91b674d..26307cdc3969 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -215,14 +215,25 @@ static inline void memalloc_noreclaim_restore(unsigned int flags)
#ifdef CONFIG_MEMBARRIER
enum {
MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY = (1U << 0),
- MEMBARRIER_STATE_SWITCH_MM = (1U << 1),
+ MEMBARRIER_STATE_PRIVATE_EXPEDITED = (1U << 1),
};
+#ifdef CONFIG_ARCH_HAS_MEMBARRIER_CALLBACKS
+#include <asm/membarrier.h>
+#endif
+
static inline void membarrier_execve(struct task_struct *t)
{
atomic_set(&t->mm->membarrier_state, 0);
}
#else
+#ifdef CONFIG_ARCH_HAS_MEMBARRIER_CALLBACKS
+static inline void membarrier_arch_switch_mm(struct mm_struct *prev,
+ struct mm_struct *next,
+ struct task_struct *tsk)
+{
+}
+#endif
static inline void membarrier_execve(struct task_struct *t)
{
}
diff --git a/init/Kconfig b/init/Kconfig
index a9a2e2c86671..837adcf075d9 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1412,6 +1412,9 @@ config USERFAULTFD
Enable the userfaultfd() system call that allows to intercept and
handle page faults in userland.
+config ARCH_HAS_MEMBARRIER_CALLBACKS
+ bool
+
config EMBEDDED
bool "Embedded system"
option allnoconfig_y
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3da7a2444a91..ead0c2135d47 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2698,16 +2698,6 @@ static struct rq *finish_task_switch(struct task_struct *prev)
prev_state = prev->state;
vtime_task_switch(prev);
perf_event_task_sched_in(prev, current);
- /*
- * The membarrier system call requires a full memory barrier
- * after storing to rq->curr, before going back to user-space.
- *
- * TODO: This smp_mb__after_unlock_lock can go away if PPC end
- * up adding a full barrier to switch_mm(), or we should figure
- * out if a smp_mb__after_unlock_lock is really the proper API
- * to use.
- */
- smp_mb__after_unlock_lock();
finish_task(prev);
finish_lock_switch(rq);
finish_arch_post_lock_switch();
diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
index 9bcbacba82a8..678577267a9a 100644
--- a/kernel/sched/membarrier.c
+++ b/kernel/sched/membarrier.c
@@ -118,6 +118,14 @@ static void membarrier_register_private_expedited(void)
if (atomic_read(&mm->membarrier_state)
& MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY)
return;
+ atomic_or(MEMBARRIER_STATE_PRIVATE_EXPEDITED, &mm->membarrier_state);
+ if (!(atomic_read(&mm->mm_users) == 1 && get_nr_threads(p) == 1)) {
+ /*
+ * Ensure all future scheduler executions will observe the
+ * new thread flag state for this process.
+ */
+ synchronize_sched();
+ }
atomic_or(MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY,
&mm->membarrier_state);
}