6.8-stable review patch. If anyone has any objections, please let me know.
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From: Steven Rostedt (Google) rostedt@goodmis.org
[ Upstream commit b70f2938242a028f8e9473781ede175486a59dc8 ]
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.l...
Cc: Masami Hiramatsu mhiramat@kernel.org Cc: Mathieu Desnoyers mathieu.desnoyers@efficios.com Fixes: 7af9ded0c2ca ("ring-buffer: Use wait_event_interruptible() in ring_buffer_wait()") Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/trace/ring_buffer.c | 34 +++++++++++++++++++++------------- 1 file changed, 21 insertions(+), 13 deletions(-)
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index ad0d475d1f570..43060a7ae15e7 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -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));