tracing: Wake up ring buffer waiters on closing of the file

When the file that represents the ring buffer is closed, there may be
waiters waiting on more input from the ring buffer. Call
ring_buffer_wake_waiters() to wake up any waiters when the file is
closed.

Link: https://lkml.kernel.org/r/20220927231825.182416969@goodmis.org
Cc: stable@vger.kernel.org
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Fixes: e30f53aad2202 ("tracing: Do not busy wait in buffer splice")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 8401dec..20749bd 100644 (file)
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -92,6 +92,7 @@ struct trace_iterator {
        unsigned int            temp_size;
        char                    *fmt;   /* modified format holder */
        unsigned int            fmt_size;
+       long                    wait_index;
 
        /* trace_seq for __print_flags() and __print_symbolic() etc. */
        struct trace_seq        tmp_seq;

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index aed7ea6..e101b07 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -8160,6 +8160,12 @@ static int tracing_buffers_release(struct inode *inode, struct file *file)
 
        __trace_array_put(iter->tr);
 
+       iter->wait_index++;
+       /* Make sure the waiters see the new wait_index */
+       smp_wmb();
+
+       ring_buffer_wake_waiters(iter->array_buffer->buffer, iter->cpu_file);
+
        if (info->spare)
                ring_buffer_free_read_page(iter->array_buffer->buffer,
                                           info->spare_cpu, info->spare);
@@ -8313,6 +8319,8 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
 
        /* did we read anything? */
        if (!spd.nr_pages) {
+               long wait_index;
+
                if (ret)
                        goto out;
 
@@ -8320,10 +8328,17 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
                if ((file->f_flags & O_NONBLOCK) || (flags & SPLICE_F_NONBLOCK))
                        goto out;
 
+               wait_index = READ_ONCE(iter->wait_index);
+
                ret = wait_on_pipe(iter, iter->tr->buffer_percent);
                if (ret)
                        goto out;
 
+               /* Make sure we see the new wait_index */
+               smp_rmb();
+               if (wait_index != iter->wait_index)
+                       goto out;
+
                goto again;
        }