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perf: Cure task_oncpu_function_call() races

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Oleg reported that on architectures with
__ARCH_WANT_INTERRUPTS_ON_CTXSW the IPI from
task_oncpu_function_call() can land before perf_event_task_sched_in()
and cause interesting situations for eg. perf_install_in_context().

This patch reworks the task_oncpu_function_call() interface to give a
more usable primitive as well as rework all its users to hopefully be
more obvious as well as remove the races.

While looking at the code I also found a number of races against
perf_event_task_sched_out() which can flip contexts between tasks so
plug those too.

Reported-and-reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2011-02-02 13:19:09 +01:00 committed by Ingo Molnar
parent b84defe603
commit fe4b04fa31
3 changed files with 172 additions and 124 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
include/linux/sched.h
View File

@ -2578,13 +2578,6 @@ static inline void inc_syscw(struct task_struct *tsk)
#define TASK_SIZE_OF(tsk) TASK_SIZE
#endif
/*
* Call the function if the target task is executing on a CPU right now:
*/
extern void task_oncpu_function_call(struct task_struct *p,
void (*func) (void *info), void *info);
#ifdef CONFIG_MM_OWNER
extern void mm_update_next_owner(struct mm_struct *mm);
extern void mm_init_owner(struct mm_struct *mm, struct task_struct *p);

260
kernel/perf_event.c
View File

@ -38,6 +38,79 @@
#include <asm/irq_regs.h>
struct remote_function_call {
struct task_struct *p;
int (*func)(void *info);
void *info;
int ret;
};
static void remote_function(void *data)
{
struct remote_function_call *tfc = data;
struct task_struct *p = tfc->p;
if (p) {
tfc->ret = -EAGAIN;
if (task_cpu(p) != smp_processor_id() || !task_curr(p))
return;
}
tfc->ret = tfc->func(tfc->info);
}
/**
* task_function_call - call a function on the cpu on which a task runs
* @p: the task to evaluate
* @func: the function to be called
* @info: the function call argument
*
* Calls the function @func when the task is currently running. This might
* be on the current CPU, which just calls the function directly
*
* returns: @func return value, or
* -ESRCH - when the process isn't running
* -EAGAIN - when the process moved away
*/
static int
task_function_call(struct task_struct *p, int (*func) (void *info), void *info)
{
struct remote_function_call data = {
.p = p,
.func = func,
.info = info,
.ret = -ESRCH, /* No such (running) process */
};
if (task_curr(p))
smp_call_function_single(task_cpu(p), remote_function, &data, 1);
return data.ret;
}
/**
* cpu_function_call - call a function on the cpu
* @func: the function to be called
* @info: the function call argument
*
* Calls the function @func on the remote cpu.
*
* returns: @func return value or -ENXIO when the cpu is offline
*/
static int cpu_function_call(int cpu, int (*func) (void *info), void *info)
{
struct remote_function_call data = {
.p = NULL,
.func = func,
.info = info,
.ret = -ENXIO, /* No such CPU */
};
smp_call_function_single(cpu, remote_function, &data, 1);
return data.ret;
}
enum event_type_t {
EVENT_FLEXIBLE = 0x1,
EVENT_PINNED = 0x2,
@ -254,7 +327,6 @@ static void perf_unpin_context(struct perf_event_context *ctx)
raw_spin_lock_irqsave(&ctx->lock, flags);
--ctx->pin_count;
raw_spin_unlock_irqrestore(&ctx->lock, flags);
put_ctx(ctx);
}
/*
@ -618,35 +690,24 @@ __get_cpu_context(struct perf_event_context *ctx)
* We disable the event on the hardware level first. After that we
* remove it from the context list.
*/
static void __perf_event_remove_from_context(void *info)
static int __perf_remove_from_context(void *info)
{
struct perf_event *event = info;
struct perf_event_context *ctx = event->ctx;
struct perf_cpu_context *cpuctx = __get_cpu_context(ctx);
/*
* If this is a task context, we need to check whether it is
* the current task context of this cpu. If not it has been
* scheduled out before the smp call arrived.
*/
if (ctx->task && cpuctx->task_ctx != ctx)
return;
raw_spin_lock(&ctx->lock);
event_sched_out(event, cpuctx, ctx);
list_del_event(event, ctx);
raw_spin_unlock(&ctx->lock);
return 0;
}
/*
* Remove the event from a task's (or a CPU's) list of events.
*
* Must be called with ctx->mutex held.
*
* CPU events are removed with a smp call. For task events we only
* call when the task is on a CPU.
*
@ -657,49 +718,48 @@ static void __perf_event_remove_from_context(void *info)
* When called from perf_event_exit_task, it's OK because the
* context has been detached from its task.
*/
static void perf_event_remove_from_context(struct perf_event *event)
static void perf_remove_from_context(struct perf_event *event)
{
struct perf_event_context *ctx = event->ctx;
struct task_struct *task = ctx->task;
lockdep_assert_held(&ctx->mutex);
if (!task) {
/*
* Per cpu events are removed via an smp call and
* the removal is always successful.
*/
smp_call_function_single(event->cpu,
__perf_event_remove_from_context,
event, 1);
cpu_function_call(event->cpu, __perf_remove_from_context, event);
return;
}
retry:
task_oncpu_function_call(task, __perf_event_remove_from_context,
event);
if (!task_function_call(task, __perf_remove_from_context, event))
return;
raw_spin_lock_irq(&ctx->lock);
/*
* If the context is active we need to retry the smp call.
* If we failed to find a running task, but find the context active now
* that we've acquired the ctx->lock, retry.
*/
if (ctx->nr_active && !list_empty(&event->group_entry)) {
if (ctx->is_active) {
raw_spin_unlock_irq(&ctx->lock);
goto retry;
}
/*
* The lock prevents that this context is scheduled in so we
* can remove the event safely, if the call above did not
* succeed.
* Since the task isn't running, its safe to remove the event, us
* holding the ctx->lock ensures the task won't get scheduled in.
*/
if (!list_empty(&event->group_entry))
list_del_event(event, ctx);
list_del_event(event, ctx);
raw_spin_unlock_irq(&ctx->lock);
}
/*
* Cross CPU call to disable a performance event
*/
static void __perf_event_disable(void *info)
static int __perf_event_disable(void *info)
{
struct perf_event *event = info;
struct perf_event_context *ctx = event->ctx;
@ -708,9 +768,12 @@ static void __perf_event_disable(void *info)
/*
* If this is a per-task event, need to check whether this
* event's task is the current task on this cpu.
*
* Can trigger due to concurrent perf_event_context_sched_out()
* flipping contexts around.
*/
if (ctx->task && cpuctx->task_ctx != ctx)
return;
return -EINVAL;
raw_spin_lock(&ctx->lock);
@ -729,6 +792,8 @@ static void __perf_event_disable(void *info)
}
raw_spin_unlock(&ctx->lock);
return 0;
}
/*
@ -753,13 +818,13 @@ void perf_event_disable(struct perf_event *event)
/*
* Disable the event on the cpu that it's on
*/
smp_call_function_single(event->cpu, __perf_event_disable,
event, 1);
cpu_function_call(event->cpu, __perf_event_disable, event);
return;
}
retry:
task_oncpu_function_call(task, __perf_event_disable, event);
if (!task_function_call(task, __perf_event_disable, event))
return;
raw_spin_lock_irq(&ctx->lock);
/*
@ -767,6 +832,11 @@ void perf_event_disable(struct perf_event *event)
*/
if (event->state == PERF_EVENT_STATE_ACTIVE) {
raw_spin_unlock_irq(&ctx->lock);
/*
* Reload the task pointer, it might have been changed by
* a concurrent perf_event_context_sched_out().
*/
task = ctx->task;
goto retry;
}
@ -778,7 +848,6 @@ void perf_event_disable(struct perf_event *event)
update_group_times(event);
event->state = PERF_EVENT_STATE_OFF;
}
raw_spin_unlock_irq(&ctx->lock);
}
@ -928,12 +997,14 @@ static void add_event_to_ctx(struct perf_event *event,
event->tstamp_stopped = tstamp;
}
static void perf_event_context_sched_in(struct perf_event_context *ctx);
/*
* Cross CPU call to install and enable a performance event
*
* Must be called with ctx->mutex held
*/
static void __perf_install_in_context(void *info)
static int __perf_install_in_context(void *info)
{
struct perf_event *event = info;
struct perf_event_context *ctx = event->ctx;
@ -942,17 +1013,12 @@ static void __perf_install_in_context(void *info)
int err;
/*
* If this is a task context, we need to check whether it is
* the current task context of this cpu. If not it has been
* scheduled out before the smp call arrived.
* Or possibly this is the right context but it isn't
* on this cpu because it had no events.
* In case we're installing a new context to an already running task,
* could also happen before perf_event_task_sched_in() on architectures
* which do context switches with IRQs enabled.
*/
if (ctx->task && cpuctx->task_ctx != ctx) {
if (cpuctx->task_ctx || ctx->task != current)
return;
cpuctx->task_ctx = ctx;
}
if (ctx->task && !cpuctx->task_ctx)
perf_event_context_sched_in(ctx);
raw_spin_lock(&ctx->lock);
ctx->is_active = 1;
@ -997,6 +1063,8 @@ static void __perf_install_in_context(void *info)
unlock:
raw_spin_unlock(&ctx->lock);
return 0;
}
/*
@ -1008,8 +1076,6 @@ static void __perf_install_in_context(void *info)
* If the event is attached to a task which is on a CPU we use a smp
* call to enable it in the task context. The task might have been
* scheduled away, but we check this in the smp call again.
*
* Must be called with ctx->mutex held.
*/
static void
perf_install_in_context(struct perf_event_context *ctx,
@ -1018,6 +1084,8 @@ perf_install_in_context(struct perf_event_context *ctx,
{
struct task_struct *task = ctx->task;
lockdep_assert_held(&ctx->mutex);
event->ctx = ctx;
if (!task) {
@ -1025,31 +1093,29 @@ perf_install_in_context(struct perf_event_context *ctx,
* Per cpu events are installed via an smp call and
* the install is always successful.
*/
smp_call_function_single(cpu, __perf_install_in_context,
event, 1);
cpu_function_call(cpu, __perf_install_in_context, event);
return;
}
retry:
task_oncpu_function_call(task, __perf_install_in_context,
event);
if (!task_function_call(task, __perf_install_in_context, event))
return;
raw_spin_lock_irq(&ctx->lock);
/*
* we need to retry the smp call.
* If we failed to find a running task, but find the context active now
* that we've acquired the ctx->lock, retry.
*/
if (ctx->is_active && list_empty(&event->group_entry)) {
if (ctx->is_active) {
raw_spin_unlock_irq(&ctx->lock);
goto retry;
}
/*
* The lock prevents that this context is scheduled in so we
* can add the event safely, if it the call above did not
* succeed.
* Since the task isn't running, its safe to add the event, us holding
* the ctx->lock ensures the task won't get scheduled in.
*/
if (list_empty(&event->group_entry))
add_event_to_ctx(event, ctx);
add_event_to_ctx(event, ctx);
raw_spin_unlock_irq(&ctx->lock);
}
@ -1078,7 +1144,7 @@ static void __perf_event_mark_enabled(struct perf_event *event,
/*
* Cross CPU call to enable a performance event
*/
static void __perf_event_enable(void *info)
static int __perf_event_enable(void *info)
{
struct perf_event *event = info;
struct perf_event_context *ctx = event->ctx;
@ -1086,18 +1152,10 @@ static void __perf_event_enable(void *info)
struct perf_cpu_context *cpuctx = __get_cpu_context(ctx);
int err;
/*
* If this is a per-task event, need to check whether this
* event's task is the current task on this cpu.
*/
if (ctx->task && cpuctx->task_ctx != ctx) {
if (cpuctx->task_ctx || ctx->task != current)
return;
cpuctx->task_ctx = ctx;
}
if (WARN_ON_ONCE(!ctx->is_active))
return -EINVAL;
raw_spin_lock(&ctx->lock);
ctx->is_active = 1;
update_context_time(ctx);
if (event->state >= PERF_EVENT_STATE_INACTIVE)
@ -1138,6 +1196,8 @@ static void __perf_event_enable(void *info)
unlock:
raw_spin_unlock(&ctx->lock);
return 0;
}
/*
@ -1158,8 +1218,7 @@ void perf_event_enable(struct perf_event *event)
/*
* Enable the event on the cpu that it's on
*/
smp_call_function_single(event->cpu, __perf_event_enable,
event, 1);
cpu_function_call(event->cpu, __perf_event_enable, event);
return;
}
@ -1178,8 +1237,15 @@ void perf_event_enable(struct perf_event *event)
event->state = PERF_EVENT_STATE_OFF;
retry:
if (!ctx->is_active) {
__perf_event_mark_enabled(event, ctx);
goto out;
}
raw_spin_unlock_irq(&ctx->lock);
task_oncpu_function_call(task, __perf_event_enable, event);
if (!task_function_call(task, __perf_event_enable, event))
return;
raw_spin_lock_irq(&ctx->lock);
@ -1187,15 +1253,14 @@ void perf_event_enable(struct perf_event *event)
* If the context is active and the event is still off,
* we need to retry the cross-call.
*/
if (ctx->is_active && event->state == PERF_EVENT_STATE_OFF)
if (ctx->is_active && event->state == PERF_EVENT_STATE_OFF) {
/*
* task could have been flipped by a concurrent
* perf_event_context_sched_out()
*/
task = ctx->task;
goto retry;
/*
* Since we have the lock this context can't be scheduled
* in, so we can change the state safely.
*/
if (event->state == PERF_EVENT_STATE_OFF)
__perf_event_mark_enabled(event, ctx);
}
out:
raw_spin_unlock_irq(&ctx->lock);
@ -1339,8 +1404,8 @@ static void perf_event_sync_stat(struct perf_event_context *ctx,
}
}
void perf_event_context_sched_out(struct task_struct *task, int ctxn,
struct task_struct *next)
static void perf_event_context_sched_out(struct task_struct *task, int ctxn,
struct task_struct *next)
{
struct perf_event_context *ctx = task->perf_event_ctxp[ctxn];
struct perf_event_context *next_ctx;
@ -1533,7 +1598,7 @@ static void task_ctx_sched_in(struct perf_event_context *ctx,
{
struct perf_cpu_context *cpuctx;
cpuctx = __get_cpu_context(ctx);
cpuctx = __get_cpu_context(ctx);
if (cpuctx->task_ctx == ctx)
return;
@ -1541,7 +1606,7 @@ static void task_ctx_sched_in(struct perf_event_context *ctx,
cpuctx->task_ctx = ctx;
}
void perf_event_context_sched_in(struct perf_event_context *ctx)
static void perf_event_context_sched_in(struct perf_event_context *ctx)
{
struct perf_cpu_context *cpuctx;
@ -1627,7 +1692,7 @@ static u64 perf_calculate_period(struct perf_event *event, u64 nsec, u64 count)
* Reduce accuracy by one bit such that @a and @b converge
* to a similar magnitude.
*/
#define REDUCE_FLS(a, b) \
#define REDUCE_FLS(a, b) \
do { \
if (a##_fls > b##_fls) { \
a >>= 1; \
@ -2213,6 +2278,9 @@ find_lively_task_by_vpid(pid_t vpid)
}
/*
* Returns a matching context with refcount and pincount.
*/
static struct perf_event_context *
find_get_context(struct pmu *pmu, struct task_struct *task, int cpu)
{
@ -2237,6 +2305,7 @@ find_get_context(struct pmu *pmu, struct task_struct *task, int cpu)
cpuctx = per_cpu_ptr(pmu->pmu_cpu_context, cpu);
ctx = &cpuctx->ctx;
get_ctx(ctx);
++ctx->pin_count;
return ctx;
}
@ -2250,6 +2319,7 @@ find_get_context(struct pmu *pmu, struct task_struct *task, int cpu)
ctx = perf_lock_task_context(task, ctxn, &flags);
if (ctx) {
unclone_ctx(ctx);
++ctx->pin_count;
raw_spin_unlock_irqrestore(&ctx->lock, flags);
}
@ -2271,8 +2341,10 @@ find_get_context(struct pmu *pmu, struct task_struct *task, int cpu)
err = -ESRCH;
else if (task->perf_event_ctxp[ctxn])
err = -EAGAIN;
else
else {
++ctx->pin_count;
rcu_assign_pointer(task->perf_event_ctxp[ctxn], ctx);
}
mutex_unlock(&task->perf_event_mutex);
if (unlikely(err)) {
@ -5950,10 +6022,10 @@ SYSCALL_DEFINE5(perf_event_open,
struct perf_event_context *gctx = group_leader->ctx;
mutex_lock(&gctx->mutex);
perf_event_remove_from_context(group_leader);
perf_remove_from_context(group_leader);
list_for_each_entry(sibling, &group_leader->sibling_list,
group_entry) {
perf_event_remove_from_context(sibling);
perf_remove_from_context(sibling);
put_ctx(gctx);
}
mutex_unlock(&gctx->mutex);
@ -5976,6 +6048,7 @@ SYSCALL_DEFINE5(perf_event_open,
perf_install_in_context(ctx, event, cpu);
++ctx->generation;
perf_unpin_context(ctx);
mutex_unlock(&ctx->mutex);
event->owner = current;
@ -6001,6 +6074,7 @@ SYSCALL_DEFINE5(perf_event_open,
return event_fd;
err_context:
perf_unpin_context(ctx);
put_ctx(ctx);
err_alloc:
free_event(event);
@ -6051,6 +6125,7 @@ perf_event_create_kernel_counter(struct perf_event_attr *attr, int cpu,
mutex_lock(&ctx->mutex);
perf_install_in_context(ctx, event, cpu);
++ctx->generation;
perf_unpin_context(ctx);
mutex_unlock(&ctx->mutex);
return event;
@ -6104,7 +6179,7 @@ __perf_event_exit_task(struct perf_event *child_event,
{
struct perf_event *parent_event;
perf_event_remove_from_context(child_event);
perf_remove_from_context(child_event);
parent_event = child_event->parent;
/*
@ -6411,7 +6486,7 @@ inherit_task_group(struct perf_event *event, struct task_struct *parent,
return 0;
}
child_ctx = child->perf_event_ctxp[ctxn];
child_ctx = child->perf_event_ctxp[ctxn];
if (!child_ctx) {
/*
* This is executed from the parent task context, so
@ -6526,6 +6601,7 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
mutex_unlock(&parent_ctx->mutex);
perf_unpin_context(parent_ctx);
put_ctx(parent_ctx);
return ret;
}
@ -6595,9 +6671,9 @@ static void __perf_event_exit_context(void *__info)
perf_pmu_rotate_stop(ctx->pmu);
list_for_each_entry_safe(event, tmp, &ctx->pinned_groups, group_entry)
__perf_event_remove_from_context(event);
__perf_remove_from_context(event);
list_for_each_entry_safe(event, tmp, &ctx->flexible_groups, group_entry)
__perf_event_remove_from_context(event);
__perf_remove_from_context(event);
}
static void perf_event_exit_cpu_context(int cpu)

29
kernel/sched.c
View File

@ -2265,27 +2265,6 @@ void kick_process(struct task_struct *p)
EXPORT_SYMBOL_GPL(kick_process);
#endif /* CONFIG_SMP */
/**
* task_oncpu_function_call - call a function on the cpu on which a task runs
* @p: the task to evaluate
* @func: the function to be called
* @info: the function call argument
*
* Calls the function @func when the task is currently running. This might
* be on the current CPU, which just calls the function directly
*/
void task_oncpu_function_call(struct task_struct *p,
void (*func) (void *info), void *info)
{
int cpu;
preempt_disable();
cpu = task_cpu(p);
if (task_curr(p))
smp_call_function_single(cpu, func, info, 1);
preempt_enable();
}
#ifdef CONFIG_SMP
/*
* ->cpus_allowed is protected by either TASK_WAKING or rq->lock held.
@ -2776,9 +2755,12 @@ static inline void
prepare_task_switch(struct rq *rq, struct task_struct *prev,
struct task_struct *next)
{
sched_info_switch(prev, next);
perf_event_task_sched_out(prev, next);
fire_sched_out_preempt_notifiers(prev, next);
prepare_lock_switch(rq, next);
prepare_arch_switch(next);
trace_sched_switch(prev, next);
}
/**
@ -2911,7 +2893,7 @@ context_switch(struct rq *rq, struct task_struct *prev,
struct mm_struct *mm, *oldmm;
prepare_task_switch(rq, prev, next);
trace_sched_switch(prev, next);
mm = next->mm;
oldmm = prev->active_mm;
/*
@ -3989,9 +3971,6 @@ asmlinkage void __sched schedule(void)
rq->skip_clock_update = 0;
if (likely(prev != next)) {
sched_info_switch(prev, next);
perf_event_task_sched_out(prev, next);
rq->nr_switches++;
rq->curr = next;
++*switch_count;