diff options
| -rw-r--r-- | kernel/events/core.c | 151 |
1 files changed, 85 insertions, 66 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c index 3eaf91b104e9..9de4d352ba8c 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -148,6 +148,13 @@ static void perf_ctx_unlock(struct perf_cpu_context *cpuctx, raw_spin_unlock(&cpuctx->ctx.lock); } +#define TASK_TOMBSTONE ((void *)-1L) + +static bool is_kernel_event(struct perf_event *event) +{ + return event->owner == TASK_TOMBSTONE; +} + /* * On task ctx scheduling... * @@ -196,31 +203,21 @@ static int event_function(void *info) struct perf_event_context *ctx = event->ctx; struct perf_cpu_context *cpuctx = __get_cpu_context(ctx); struct perf_event_context *task_ctx = cpuctx->task_ctx; + int ret = 0; WARN_ON_ONCE(!irqs_disabled()); + perf_ctx_lock(cpuctx, task_ctx); /* * Since we do the IPI call without holding ctx->lock things can have * changed, double check we hit the task we set out to hit. - * - * If ctx->task == current, we know things must remain valid because - * we have IRQs disabled so we cannot schedule. */ if (ctx->task) { - if (ctx->task != current) - return -EAGAIN; - - WARN_ON_ONCE(task_ctx != ctx); - } else { - WARN_ON_ONCE(&cpuctx->ctx != ctx); - } + if (ctx->task != current) { + ret = -EAGAIN; + goto unlock; + } - perf_ctx_lock(cpuctx, task_ctx); - /* - * Now that we hold locks, double check state. Paranoia pays. - */ - if (task_ctx) { - WARN_ON_ONCE(task_ctx->task != current); /* * We only use event_function_call() on established contexts, * and event_function() is only ever called when active (or @@ -233,12 +230,16 @@ static int event_function(void *info) * And since we have ctx->is_active, cpuctx->task_ctx must * match. */ - WARN_ON_ONCE(cpuctx->task_ctx != task_ctx); + WARN_ON_ONCE(task_ctx != ctx); + } else { + WARN_ON_ONCE(&cpuctx->ctx != ctx); } + efs->func(event, cpuctx, ctx, efs->data); +unlock: perf_ctx_unlock(cpuctx, task_ctx); - return 0; + return ret; } static void event_function_local(struct perf_event *event, event_f func, void *data) @@ -256,7 +257,7 @@ static void event_function_local(struct perf_event *event, event_f func, void *d static void event_function_call(struct perf_event *event, event_f func, void *data) { struct perf_event_context *ctx = event->ctx; - struct task_struct *task = ctx->task; + struct task_struct *task = READ_ONCE(ctx->task); /* verified in event_function */ struct event_function_struct efs = { .event = event, .func = func, @@ -278,30 +279,28 @@ static void event_function_call(struct perf_event *event, event_f func, void *da } again: + if (task == TASK_TOMBSTONE) + return; + if (!task_function_call(task, event_function, &efs)) return; raw_spin_lock_irq(&ctx->lock); - if (ctx->is_active) { - /* - * Reload the task pointer, it might have been changed by - * a concurrent perf_event_context_sched_out(). - */ - task = ctx->task; - raw_spin_unlock_irq(&ctx->lock); - goto again; + /* + * Reload the task pointer, it might have been changed by + * a concurrent perf_event_context_sched_out(). + */ + task = ctx->task; + if (task != TASK_TOMBSTONE) { + if (ctx->is_active) { + raw_spin_unlock_irq(&ctx->lock); + goto again; + } + func(event, NULL, ctx, data); } - func(event, NULL, ctx, data); raw_spin_unlock_irq(&ctx->lock); } -#define EVENT_OWNER_KERNEL ((void *) -1) - -static bool is_kernel_event(struct perf_event *event) -{ - return event->owner == EVENT_OWNER_KERNEL; -} - #define PERF_FLAG_ALL (PERF_FLAG_FD_NO_GROUP |\ PERF_FLAG_FD_OUTPUT |\ PERF_FLAG_PID_CGROUP |\ @@ -1025,7 +1024,7 @@ static void put_ctx(struct perf_event_context *ctx) if (atomic_dec_and_test(&ctx->refcount)) { if (ctx->parent_ctx) put_ctx(ctx->parent_ctx); - if (ctx->task) + if (ctx->task && ctx->task != TASK_TOMBSTONE) put_task_struct(ctx->task); call_rcu(&ctx->rcu_head, free_ctx); } @@ -1186,6 +1185,7 @@ static u64 primary_event_id(struct perf_event *event) /* * Get the perf_event_context for a task and lock it. + * * This has to cope with with the fact that until it is locked, * the context could get moved to another task. */ @@ -1226,10 +1226,13 @@ retry: goto retry; } - if (!atomic_inc_not_zero(&ctx->refcount)) { + if (ctx->task == TASK_TOMBSTONE || + !atomic_inc_not_zero(&ctx->refcount)) { raw_spin_unlock(&ctx->lock); ctx = NULL; } + + WARN_ON_ONCE(ctx->task != task); } rcu_read_unlock(); if (!ctx) @@ -2140,23 +2143,27 @@ static int __perf_install_in_context(void *info) struct perf_cpu_context *cpuctx = __get_cpu_context(ctx); struct perf_event_context *task_ctx = cpuctx->task_ctx; + raw_spin_lock(&cpuctx->ctx.lock); if (ctx->task) { + raw_spin_lock(&ctx->lock); /* * If we hit the 'wrong' task, we've since scheduled and * everything should be sorted, nothing to do! */ + task_ctx = ctx; if (ctx->task != current) - return 0; + goto unlock; /* * If task_ctx is set, it had better be to us. */ WARN_ON_ONCE(cpuctx->task_ctx != ctx && cpuctx->task_ctx); - task_ctx = ctx; + } else if (task_ctx) { + raw_spin_lock(&task_ctx->lock); } - perf_ctx_lock(cpuctx, task_ctx); ctx_resched(cpuctx, task_ctx); +unlock: perf_ctx_unlock(cpuctx, task_ctx); return 0; @@ -2188,6 +2195,17 @@ perf_install_in_context(struct perf_event_context *ctx, * happened and that will have taken care of business. */ raw_spin_lock_irq(&ctx->lock); + task = ctx->task; + /* + * Worse, we cannot even rely on the ctx actually existing anymore. If + * between find_get_context() and perf_install_in_context() the task + * went through perf_event_exit_task() its dead and we should not be + * adding new events. + */ + if (task == TASK_TOMBSTONE) { + raw_spin_unlock_irq(&ctx->lock); + return; + } update_context_time(ctx); /* * Update cgrp time only if current cgrp matches event->cgrp. @@ -2195,7 +2213,6 @@ perf_install_in_context(struct perf_event_context *ctx, */ update_cgrp_time_from_event(event); add_event_to_ctx(event, ctx); - task = ctx->task; raw_spin_unlock_irq(&ctx->lock); if (task) @@ -2538,17 +2555,21 @@ static void perf_event_context_sched_out(struct task_struct *task, int ctxn, raw_spin_lock(&ctx->lock); raw_spin_lock_nested(&next_ctx->lock, SINGLE_DEPTH_NESTING); if (context_equiv(ctx, next_ctx)) { - /* - * XXX do we need a memory barrier of sorts - * wrt to rcu_dereference() of perf_event_ctxp - */ - task->perf_event_ctxp[ctxn] = next_ctx; - next->perf_event_ctxp[ctxn] = ctx; - ctx->task = next; - next_ctx->task = task; + WRITE_ONCE(ctx->task, next); + WRITE_ONCE(next_ctx->task, task); swap(ctx->task_ctx_data, next_ctx->task_ctx_data); + /* + * RCU_INIT_POINTER here is safe because we've not + * modified the ctx and the above modification of + * ctx->task and ctx->task_ctx_data are immaterial + * since those values are always verified under + * ctx->lock which we're now holding. + */ + RCU_INIT_POINTER(task->perf_event_ctxp[ctxn], next_ctx); + RCU_INIT_POINTER(next->perf_event_ctxp[ctxn], ctx); + do_switch = 0; perf_event_sync_stat(ctx, next_ctx); @@ -8545,7 +8566,7 @@ perf_event_create_kernel_counter(struct perf_event_attr *attr, int cpu, } /* Mark owner so we could distinguish it from user events. */ - event->owner = EVENT_OWNER_KERNEL; + event->owner = TASK_TOMBSTONE; account_event(event); @@ -8725,28 +8746,26 @@ __perf_event_exit_task(struct perf_event *child_event, static void perf_event_exit_task_context(struct task_struct *child, int ctxn) { - struct perf_event *child_event, *next; struct perf_event_context *child_ctx, *clone_ctx = NULL; + struct perf_event *child_event, *next; + unsigned long flags; - if (likely(!child->perf_event_ctxp[ctxn])) + WARN_ON_ONCE(child != current); + + child_ctx = perf_lock_task_context(child, ctxn, &flags); + if (!child_ctx) return; - local_irq_disable(); - WARN_ON_ONCE(child != current); - /* - * We can't reschedule here because interrupts are disabled, - * and child must be current. - */ - child_ctx = rcu_dereference_raw(child->perf_event_ctxp[ctxn]); + task_ctx_sched_out(__get_cpu_context(child_ctx), child_ctx); /* - * Take the context lock here so that if find_get_context is - * reading child->perf_event_ctxp, we wait until it has - * incremented the context's refcount before we do put_ctx below. + * Now that the context is inactive, destroy the task <-> ctx relation + * and mark the context dead. */ - raw_spin_lock(&child_ctx->lock); - task_ctx_sched_out(__get_cpu_context(child_ctx), child_ctx); - child->perf_event_ctxp[ctxn] = NULL; + RCU_INIT_POINTER(child->perf_event_ctxp[ctxn], NULL); + put_ctx(child_ctx); /* cannot be last */ + WRITE_ONCE(child_ctx->task, TASK_TOMBSTONE); + put_task_struct(current); /* cannot be last */ /* * If this context is a clone; unclone it so it can't get @@ -8755,7 +8774,7 @@ static void perf_event_exit_task_context(struct task_struct *child, int ctxn) */ clone_ctx = unclone_ctx(child_ctx); update_context_time(child_ctx); - raw_spin_unlock_irq(&child_ctx->lock); + raw_spin_unlock_irqrestore(&child_ctx->lock, flags); if (clone_ctx) put_ctx(clone_ctx); |