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ring-buffer: Make wake once of ring_buffer_wait() more robust 

The default behavior of ring_buffer_wait() when passed a NULL "cond"
parameter is to exit the function the first time it is woken up. The
current implementation uses a counter that starts at zero and when it is
greater than one it exits the wait_event_interruptible().

But this relies on the internal working of wait_event_interruptible() as
that code basically has:

  if (cond)
    return;
  prepare_to_wait();
  if (!cond)
    schedule();
  finish_wait();

That is, cond is called twice before it sleeps. The default cond of
ring_buffer_wait() needs to account for that and wait for its counter to
increment twice before exiting.

Instead, use the seq/atomic_inc logic that is used by the tracing code
that calls this function. Add an atomic_t seq to rb_irq_work and when cond
is NULL, have the default callback take a descriptor as its data that
holds the rbwork and the value of the seq when it started.

The wakeups will now increment the rbwork->seq and the cond callback will
simply check if that number is different, and no longer have to rely on
the implementation of wait_event_interruptible().

Link: https://lore.kernel.org/linux-trace-kernel/20240315063115.6cb5d205@gandalf.local.home

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Fixes: 7af9ded0c2 ("ring-buffer: Use wait_event_interruptible() in ring_buffer_wait()")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt (Google) 2024-03-15 06:31:15 -04:00
parent f1e30cb636
commit b70f293824
1 changed files with 21 additions and 13 deletions
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34
kernel/trace/ring_buffer.c
View File

@ -384,6 +384,7 @@ struct rb_irq_work {
struct irq_work work;
wait_queue_head_t waiters;
wait_queue_head_t full_waiters;
atomic_t seq;
bool waiters_pending;
bool full_waiters_pending;
bool wakeup_full;
@ -753,6 +754,9 @@ static void rb_wake_up_waiters(struct irq_work *work)
{
struct rb_irq_work *rbwork = container_of(work, struct rb_irq_work, work);
/* For waiters waiting for the first wake up */
(void)atomic_fetch_inc_release(&rbwork->seq);
wake_up_all(&rbwork->waiters);
if (rbwork->full_waiters_pending || rbwork->wakeup_full) {
/* Only cpu_buffer sets the above flags */
@ -881,20 +885,21 @@ rb_wait_cond(struct rb_irq_work *rbwork, struct trace_buffer *buffer,
return false;
}
struct rb_wait_data {
struct rb_irq_work *irq_work;
int seq;
};
/*
* The default wait condition for ring_buffer_wait() is to just to exit the
* wait loop the first time it is woken up.
*/
static bool rb_wait_once(void *data)
{
long *once = data;
struct rb_wait_data *rdata = data;
struct rb_irq_work *rbwork = rdata->irq_work;
/* wait_event() actually calls this twice before scheduling*/
if (*once > 1)
return true;
(*once)++;
return false;
return atomic_read_acquire(&rbwork->seq) != rdata->seq;
}
/**
@ -915,14 +920,9 @@ int ring_buffer_wait(struct trace_buffer *buffer, int cpu, int full,
struct ring_buffer_per_cpu *cpu_buffer;
struct wait_queue_head *waitq;
struct rb_irq_work *rbwork;
long once = 0;
struct rb_wait_data rdata;
int ret = 0;
if (!cond) {
cond = rb_wait_once;
data = &once;
}
/*
* Depending on what the caller is waiting for, either any
* data in any cpu buffer, or a specific buffer, put the
@ -944,6 +944,14 @@ int ring_buffer_wait(struct trace_buffer *buffer, int cpu, int full,
else
waitq = &rbwork->waiters;
/* Set up to exit loop as soon as it is woken */
if (!cond) {
cond = rb_wait_once;
rdata.irq_work = rbwork;
rdata.seq = atomic_read_acquire(&rbwork->seq);
data = &rdata;
}
ret = wait_event_interruptible((*waitq),
rb_wait_cond(rbwork, buffer, cpu, full, cond, data));