tracing: Do not busy wait in buffer splice
On a !PREEMPT kernel, attempting to use trace-cmd results in a soft
lockup:
# trace-cmd record -e raw_syscalls:* -F false
NMI watchdog: BUG: soft lockup - CPU#0 stuck for 22s! [trace-cmd:61]
...
Call Trace:
[<ffffffff8105b580>] ? __wake_up_common+0x90/0x90
[<ffffffff81092e25>] wait_on_pipe+0x35/0x40
[<ffffffff810936e3>] tracing_buffers_splice_read+0x2e3/0x3c0
[<ffffffff81093300>] ? tracing_stats_read+0x2a0/0x2a0
[<ffffffff812d10ab>] ? _raw_spin_unlock+0x2b/0x40
[<ffffffff810dc87b>] ? do_read_fault+0x21b/0x290
[<ffffffff810de56a>] ? handle_mm_fault+0x2ba/0xbd0
[<ffffffff81095c80>] ? trace_event_buffer_lock_reserve+0x40/0x80
[<ffffffff810951e2>] ? trace_buffer_lock_reserve+0x22/0x60
[<ffffffff81095c80>] ? trace_event_buffer_lock_reserve+0x40/0x80
[<ffffffff8112415d>] do_splice_to+0x6d/0x90
[<ffffffff81126971>] SyS_splice+0x7c1/0x800
[<ffffffff812d1edd>] tracesys_phase2+0xd3/0xd8
The problem is this: tracing_buffers_splice_read() calls
ring_buffer_wait() to wait for data in the ring buffers. The buffers
are not empty so ring_buffer_wait() returns immediately. But
tracing_buffers_splice_read() calls ring_buffer_read_page() with full=1,
meaning it only wants to read a full page. When the full page is not
available, tracing_buffers_splice_read() tries to wait again with
ring_buffer_wait(), which again returns immediately, and so on.
Fix this by adding a "full" argument to ring_buffer_wait() which will
make ring_buffer_wait() wait until the writer has left the reader's
page, i.e. until full-page reads will succeed.
Link: http://lkml.kernel.org/r/1415645194-25379-1-git-send-email-rabin@rab.in
Cc: stable@vger.kernel.org # 3.16+
Fixes: b1169cc69ba9 ("tracing: Remove mock up poll wait function")
Signed-off-by: Rabin Vincent <rabin@rab.in>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 8a52839..1520933 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1076,13 +1076,14 @@
}
#endif /* CONFIG_TRACER_MAX_TRACE */
-static int wait_on_pipe(struct trace_iterator *iter)
+static int wait_on_pipe(struct trace_iterator *iter, bool full)
{
/* Iterators are static, they should be filled or empty */
if (trace_buffer_iter(iter, iter->cpu_file))
return 0;
- return ring_buffer_wait(iter->trace_buffer->buffer, iter->cpu_file);
+ return ring_buffer_wait(iter->trace_buffer->buffer, iter->cpu_file,
+ full);
}
#ifdef CONFIG_FTRACE_STARTUP_TEST
@@ -4434,15 +4435,12 @@
mutex_unlock(&iter->mutex);
- ret = wait_on_pipe(iter);
+ ret = wait_on_pipe(iter, false);
mutex_lock(&iter->mutex);
if (ret)
return ret;
-
- if (signal_pending(current))
- return -EINTR;
}
return 1;
@@ -5372,16 +5370,12 @@
goto out_unlock;
}
mutex_unlock(&trace_types_lock);
- ret = wait_on_pipe(iter);
+ ret = wait_on_pipe(iter, false);
mutex_lock(&trace_types_lock);
if (ret) {
size = ret;
goto out_unlock;
}
- if (signal_pending(current)) {
- size = -EINTR;
- goto out_unlock;
- }
goto again;
}
size = 0;
@@ -5587,14 +5581,11 @@
goto out;
}
mutex_unlock(&trace_types_lock);
- ret = wait_on_pipe(iter);
+ ret = wait_on_pipe(iter, true);
mutex_lock(&trace_types_lock);
if (ret)
goto out;
- if (signal_pending(current)) {
- ret = -EINTR;
- goto out;
- }
+
goto again;
}