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perf: Enqueue SIGTRAP always via task_work.

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A signal is delivered by raising irq_work() which works from any context
including NMI. irq_work() can be delayed if the architecture does not
provide an interrupt vector. In order not to lose a signal, the signal
is injected via task_work during event_sched_out().

Instead going via irq_work, the signal could be added directly via
task_work. The signal is sent to current and can be enqueued on its
return path to userland.

Queue signal via task_work and consider possible NMI context. Remove
perf_event::pending_sigtrap and and use perf_event::pending_work
instead.

Reported-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Marco Elver <elver@google.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Link: https://lore.kernel.org/r/20240704170424.1466941-4-bigeasy@linutronix.de
This commit is contained in:
Sebastian Andrzej Siewior 2024-07-04 19:03:37 +02:00 committed by Peter Zijlstra
parent 466e4d801c
commit c5d93d23a2
2 changed files with 11 additions and 23 deletions
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3
include/linux/perf_event.h
View File

@ -781,7 +781,6 @@ struct perf_event {
unsigned int pending_wakeup;
unsigned int pending_kill;
unsigned int pending_disable;
unsigned int pending_sigtrap;
unsigned long pending_addr; /* SIGTRAP */
struct irq_work pending_irq;
struct callback_head pending_task;
@ -963,7 +962,7 @@ struct perf_event_context {
struct rcu_head rcu_head;
/*
* Sum (event->pending_sigtrap + event->pending_work)
* Sum (event->pending_work + event->pending_work)
*
* The SIGTRAP is targeted at ctx->task, as such it won't do changing
* that until the signal is delivered.

31
kernel/events/core.c
View File

@ -2283,17 +2283,6 @@ event_sched_out(struct perf_event *event, struct perf_event_context *ctx)
state = PERF_EVENT_STATE_OFF;
}
if (event->pending_sigtrap) {
event->pending_sigtrap = 0;
if (state != PERF_EVENT_STATE_OFF &&
!event->pending_work &&
!task_work_add(current, &event->pending_task, TWA_RESUME)) {
event->pending_work = 1;
} else {
local_dec(&event->ctx->nr_pending);
}
}
perf_event_set_state(event, state);
if (!is_software_event(event))
@ -6776,11 +6765,6 @@ static void __perf_pending_irq(struct perf_event *event)
* Yay, we hit home and are in the context of the event.
*/
if (cpu == smp_processor_id()) {
if (event->pending_sigtrap) {
event->pending_sigtrap = 0;
perf_sigtrap(event);
local_dec(&event->ctx->nr_pending);
}
if (event->pending_disable) {
event->pending_disable = 0;
perf_event_disable_local(event);
@ -9721,21 +9705,26 @@ static int __perf_event_overflow(struct perf_event *event,
*/
bool valid_sample = sample_is_allowed(event, regs);
unsigned int pending_id = 1;
enum task_work_notify_mode notify_mode;
if (regs)
pending_id = hash32_ptr((void *)instruction_pointer(regs)) ?: 1;
if (!event->pending_sigtrap) {
event->pending_sigtrap = pending_id;
notify_mode = in_nmi() ? TWA_NMI_CURRENT : TWA_RESUME;
if (!event->pending_work &&
!task_work_add(current, &event->pending_task, notify_mode)) {
event->pending_work = pending_id;
local_inc(&event->ctx->nr_pending);
event->pending_addr = 0;
if (valid_sample && (data->sample_flags & PERF_SAMPLE_ADDR))
event->pending_addr = data->addr;
irq_work_queue(&event->pending_irq);
} else if (event->attr.exclude_kernel && valid_sample) {
/*
* Should not be able to return to user space without
* consuming pending_sigtrap; with exceptions:
* consuming pending_work; with exceptions:
*
* 1. Where !exclude_kernel, events can overflow again
* in the kernel without returning to user space.
@ -9745,7 +9734,7 @@ static int __perf_event_overflow(struct perf_event *event,
* To approximate progress (with false negatives),
* check 32-bit hash of the current IP.
*/
WARN_ON_ONCE(event->pending_sigtrap != pending_id);
WARN_ON_ONCE(event->pending_work != pending_id);
}
}