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rseq/membarrier: Add MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ

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This patchset is based on Google-internal RSEQ work done by Paul
Turner and Andrew Hunter.

When working with per-CPU RSEQ-based memory allocations, it is
sometimes important to make sure that a global memory location is no
longer accessed from RSEQ critical sections. For example, there can be
two per-CPU lists, one is "active" and accessed per-CPU, while another
one is inactive and worked on asynchronously "off CPU" (e.g.  garbage
collection is performed). Then at some point the two lists are
swapped, and a fast RCU-like mechanism is required to make sure that
the previously active list is no longer accessed.

This patch introduces such a mechanism: in short, membarrier() syscall
issues an IPI to a CPU, restarting a potentially active RSEQ critical
section on the CPU.

Signed-off-by: Peter Oskolkov <posk@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lkml.kernel.org/r/20200923233618.2572849-1-posk@google.com
This commit is contained in:
Peter Oskolkov 2020-09-23 16:36:16 -07:00 committed by Peter Zijlstra
parent 233e7aca4c
commit 2a36ab717e
4 changed files with 136 additions and 31 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
include/linux/sched/mm.h
View File

@ -348,10 +348,13 @@ enum {
MEMBARRIER_STATE_GLOBAL_EXPEDITED = (1U << 3),
MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY = (1U << 4),
MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE = (1U << 5),
MEMBARRIER_STATE_PRIVATE_EXPEDITED_RSEQ_READY = (1U << 6),
MEMBARRIER_STATE_PRIVATE_EXPEDITED_RSEQ = (1U << 7),
};
enum {
MEMBARRIER_FLAG_SYNC_CORE = (1U << 0),
MEMBARRIER_FLAG_RSEQ = (1U << 1),
};
#ifdef CONFIG_ARCH_HAS_MEMBARRIER_CALLBACKS

2
include/linux/syscalls.h
View File

@ -974,7 +974,7 @@ asmlinkage long sys_execveat(int dfd, const char __user *filename,
const char __user *const __user *argv,
const char __user *const __user *envp, int flags);
asmlinkage long sys_userfaultfd(int flags);
asmlinkage long sys_membarrier(int cmd, int flags);
asmlinkage long sys_membarrier(int cmd, unsigned int flags, int cpu_id);
asmlinkage long sys_mlock2(unsigned long start, size_t len, int flags);
asmlinkage long sys_copy_file_range(int fd_in, loff_t __user *off_in,
int fd_out, loff_t __user *off_out,

26
include/uapi/linux/membarrier.h
View File

@ -114,6 +114,26 @@
* If this command is not implemented by an
* architecture, -EINVAL is returned.
* Returns 0 on success.
* @MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ:
* Ensure the caller thread, upon return from
* system call, that all its running thread
* siblings have any currently running rseq
* critical sections restarted if @flags
* parameter is 0; if @flags parameter is
* MEMBARRIER_CMD_FLAG_CPU,
* then this operation is performed only
* on CPU indicated by @cpu_id. If this command is
* not implemented by an architecture, -EINVAL
* is returned. A process needs to register its
* intent to use the private expedited rseq
* command prior to using it, otherwise
* this command returns -EPERM.
* @MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ:
* Register the process intent to use
* MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ.
* If this command is not implemented by an
* architecture, -EINVAL is returned.
* Returns 0 on success.
* @MEMBARRIER_CMD_SHARED:
* Alias to MEMBARRIER_CMD_GLOBAL. Provided for
* header backward compatibility.
@ -131,9 +151,15 @@ enum membarrier_cmd {
MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED = (1 << 4),
MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE = (1 << 5),
MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE = (1 << 6),
MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ = (1 << 7),
MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ = (1 << 8),
/* Alias for header backward compatibility. */
MEMBARRIER_CMD_SHARED = MEMBARRIER_CMD_GLOBAL,
};
enum membarrier_cmd_flag {
MEMBARRIER_CMD_FLAG_CPU = (1 << 0),
};
#endif /* _UAPI_LINUX_MEMBARRIER_H */

136
kernel/sched/membarrier.c
View File

@ -18,6 +18,14 @@
#define MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK 0
#endif
#ifdef CONFIG_RSEQ
#define MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ_BITMASK \
(MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ \
| MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ_BITMASK)
#else
#define MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ_BITMASK 0
#endif
#define MEMBARRIER_CMD_BITMASK \
(MEMBARRIER_CMD_GLOBAL | MEMBARRIER_CMD_GLOBAL_EXPEDITED \
| MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED \
@ -30,6 +38,11 @@ static void ipi_mb(void *info)
smp_mb(); /* IPIs should be serializing but paranoid. */
}
static void ipi_rseq(void *info)
{
rseq_preempt(current);
}
static void ipi_sync_rq_state(void *info)
{
struct mm_struct *mm = (struct mm_struct *) info;
@ -129,19 +142,27 @@ static int membarrier_global_expedited(void)
return 0;
}
static int membarrier_private_expedited(int flags)
static int membarrier_private_expedited(int flags, int cpu_id)
{
int cpu;
cpumask_var_t tmpmask;
struct mm_struct *mm = current->mm;
smp_call_func_t ipi_func = ipi_mb;
if (flags & MEMBARRIER_FLAG_SYNC_CORE) {
if (flags == MEMBARRIER_FLAG_SYNC_CORE) {
if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE))
return -EINVAL;
if (!(atomic_read(&mm->membarrier_state) &
MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY))
return -EPERM;
} else if (flags == MEMBARRIER_FLAG_RSEQ) {
if (!IS_ENABLED(CONFIG_RSEQ))
return -EINVAL;
if (!(atomic_read(&mm->membarrier_state) &
MEMBARRIER_STATE_PRIVATE_EXPEDITED_RSEQ_READY))
return -EPERM;
ipi_func = ipi_rseq;
} else {
WARN_ON_ONCE(flags);
if (!(atomic_read(&mm->membarrier_state) &
MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY))
return -EPERM;
@ -156,35 +177,59 @@ static int membarrier_private_expedited(int flags)
*/
smp_mb(); /* system call entry is not a mb. */
if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL))
if (cpu_id < 0 && !zalloc_cpumask_var(&tmpmask, GFP_KERNEL))
return -ENOMEM;
cpus_read_lock();
rcu_read_lock();
for_each_online_cpu(cpu) {
if (cpu_id >= 0) {
struct task_struct *p;
/*
* Skipping the current CPU is OK even through we can be
* migrated at any point. The current CPU, at the point
* where we read raw_smp_processor_id(), is ensured to
* be in program order with respect to the caller
* thread. Therefore, we can skip this CPU from the
* iteration.
*/
if (cpu == raw_smp_processor_id())
continue;
p = rcu_dereference(cpu_rq(cpu)->curr);
if (p && p->mm == mm)
__cpumask_set_cpu(cpu, tmpmask);
if (cpu_id >= nr_cpu_ids || !cpu_online(cpu_id))
goto out;
if (cpu_id == raw_smp_processor_id())
goto out;
rcu_read_lock();
p = rcu_dereference(cpu_rq(cpu_id)->curr);
if (!p || p->mm != mm) {
rcu_read_unlock();
goto out;
}
rcu_read_unlock();
} else {
int cpu;
rcu_read_lock();
for_each_online_cpu(cpu) {
struct task_struct *p;
/*
* Skipping the current CPU is OK even through we can be
* migrated at any point. The current CPU, at the point
* where we read raw_smp_processor_id(), is ensured to
* be in program order with respect to the caller
* thread. Therefore, we can skip this CPU from the
* iteration.
*/
if (cpu == raw_smp_processor_id())
continue;
p = rcu_dereference(cpu_rq(cpu)->curr);
if (p && p->mm == mm)
__cpumask_set_cpu(cpu, tmpmask);
}
rcu_read_unlock();
}
rcu_read_unlock();
preempt_disable();
smp_call_function_many(tmpmask, ipi_mb, NULL, 1);
if (cpu_id >= 0)
smp_call_function_single(cpu_id, ipi_func, NULL, 1);
else
smp_call_function_many(tmpmask, ipi_func, NULL, 1);
preempt_enable();
free_cpumask_var(tmpmask);
out:
if (cpu_id < 0)
free_cpumask_var(tmpmask);
cpus_read_unlock();
/*
@ -283,11 +328,18 @@ static int membarrier_register_private_expedited(int flags)
set_state = MEMBARRIER_STATE_PRIVATE_EXPEDITED,
ret;
if (flags & MEMBARRIER_FLAG_SYNC_CORE) {
if (flags == MEMBARRIER_FLAG_SYNC_CORE) {
if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE))
return -EINVAL;
ready_state =
MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY;
} else if (flags == MEMBARRIER_FLAG_RSEQ) {
if (!IS_ENABLED(CONFIG_RSEQ))
return -EINVAL;
ready_state =
MEMBARRIER_STATE_PRIVATE_EXPEDITED_RSEQ_READY;
} else {
WARN_ON_ONCE(flags);
}
/*
@ -299,6 +351,8 @@ static int membarrier_register_private_expedited(int flags)
return 0;
if (flags & MEMBARRIER_FLAG_SYNC_CORE)
set_state |= MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE;
if (flags & MEMBARRIER_FLAG_RSEQ)
set_state |= MEMBARRIER_STATE_PRIVATE_EXPEDITED_RSEQ;
atomic_or(set_state, &mm->membarrier_state);
ret = sync_runqueues_membarrier_state(mm);
if (ret)
@ -310,8 +364,15 @@ static int membarrier_register_private_expedited(int flags)
/**
* sys_membarrier - issue memory barriers on a set of threads
* @cmd: Takes command values defined in enum membarrier_cmd.
* @flags: Currently needs to be 0. For future extensions.
* @cmd: Takes command values defined in enum membarrier_cmd.
* @flags: Currently needs to be 0 for all commands other than
* MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ: in the latter
* case it can be MEMBARRIER_CMD_FLAG_CPU, indicating that @cpu_id
* contains the CPU on which to interrupt (= restart)
* the RSEQ critical section.
* @cpu_id: if @flags == MEMBARRIER_CMD_FLAG_CPU, indicates the cpu on which
* RSEQ CS should be interrupted (@cmd must be
* MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ).
*
* If this system call is not implemented, -ENOSYS is returned. If the
* command specified does not exist, not available on the running
@ -337,10 +398,21 @@ static int membarrier_register_private_expedited(int flags)
* smp_mb() X O O
* sys_membarrier() O O O
*/
SYSCALL_DEFINE2(membarrier, int, cmd, int, flags)
SYSCALL_DEFINE3(membarrier, int, cmd, unsigned int, flags, int, cpu_id)
{
if (unlikely(flags))
return -EINVAL;
switch (cmd) {
case MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ:
if (unlikely(flags && flags != MEMBARRIER_CMD_FLAG_CPU))
return -EINVAL;
break;
default:
if (unlikely(flags))
return -EINVAL;
}
if (!(flags & MEMBARRIER_CMD_FLAG_CPU))
cpu_id = -1;
switch (cmd) {
case MEMBARRIER_CMD_QUERY:
{
@ -362,13 +434,17 @@ SYSCALL_DEFINE2(membarrier, int, cmd, int, flags)
case MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED:
return membarrier_register_global_expedited();
case MEMBARRIER_CMD_PRIVATE_EXPEDITED:
return membarrier_private_expedited(0);
return membarrier_private_expedited(0, cpu_id);
case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED:
return membarrier_register_private_expedited(0);
case MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE:
return membarrier_private_expedited(MEMBARRIER_FLAG_SYNC_CORE);
return membarrier_private_expedited(MEMBARRIER_FLAG_SYNC_CORE, cpu_id);
case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE:
return membarrier_register_private_expedited(MEMBARRIER_FLAG_SYNC_CORE);
case MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ:
return membarrier_private_expedited(MEMBARRIER_FLAG_RSEQ, cpu_id);
case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ:
return membarrier_register_private_expedited(MEMBARRIER_FLAG_RSEQ);
default:
return -EINVAL;
}