[PATCH v2 0/2] tracing: Do not clean up hiter in mmiotrace read function

[PATCH v2 0/2] tracing: Do not clean up hiter in mmiotrace read function

[Steven Rostedt]

When the mmiotrace trace was first created, it allocated a descriptor in
its pipe_open() method. Since there was no pipe_close() method when it was
created (in May of 2008, and pipe_close() was added in December of 2009),
it cleaned up the allocated descriptors in the read.

Now that the clean up is in the pipe_close() method that now exists,
remove the clean up from the read as it is no longer needed.

Also simplify the code by inverting the early exit conditional into a
conditional to perform the logic and get rid of the goto.

Link: https://lore.kernel.org/all/20260715143604.14481-1-gaikwad.dcg@gmail.com/
Link: https://lore.kernel.org/all/20260721211143.36dbd559@gandalf.local.home/

Changse since v1: https://lore.kernel.org/linux-trace-kernel/20260721212010.76e9ed61@gandalf.local.home/

- Broke it up into two patches. Nothing else changed.

Steven Rostedt (2):
      tracing: Do not clean up hiter in mmiotrace read function
      tracing: Invert the logic in mmio_read() to get rid of the goto

----
 kernel/trace/trace_mmiotrace.c | 14 +++-----------
 1 file changed, 3 insertions(+), 11 deletions(-)

[PATCH v2 1/2] tracing: Do not clean up hiter in mmiotrace read function

[Steven Rostedt]

From: Steven Rostedt <rostedt@goodmis.org>

When the mmiotrace trace was first created, it allocated a descriptor in
its pipe_open() method. Since there was no pipe_close() method when it was
created (in May of 2008, and pipe_close() was added in December of 2009),
it cleaned up the allocated descriptors in the read.

Now that the clean up is in the pipe_close() method that now exists,
remove the clean up from the read as it is no longer needed.

Link: https://lore.kernel.org/all/20260715143604.14481-1-gaikwad.dcg@gmail.com/
Link: https://lore.kernel.org/all/20260721211143.36dbd559@gandalf.local.home/

Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
Changses since v1 : https://patch.msgid.link/20260721212010.76e9ed61@gandalf.local.home

- Broke it up into two patches

 kernel/trace/trace_mmiotrace.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/kernel/trace/trace_mmiotrace.c b/kernel/trace/trace_mmiotrace.c
index 77120d467e11..0034d6af3d9d 100644
--- a/kernel/trace/trace_mmiotrace.c
+++ b/kernel/trace/trace_mmiotrace.c
@@ -152,11 +152,6 @@ static ssize_t mmio_read(struct trace_iterator *iter, struct file *filp,
 	mmio_print_pcidev(s, hiter->dev);
 	hiter->dev = pci_get_device(PCI_ANY_ID, PCI_ANY_ID, hiter->dev);
 
-	if (!hiter->dev) {
-		destroy_header_iter(hiter);
-		iter->private = NULL;
-	}
-
 print_out:
 	ret = trace_seq_to_user(s, ubuf, cnt);
 	return (ret == -EBUSY) ? 0 : ret;
-- 
2.53.0

[PATCH v2 2/2] tracing: Invert the logic in mmio_read() to get rid of the goto

[Steven Rostedt]

From: Steven Rostedt <rostedt@goodmis.org>

Simplify the logic by removing the goto in the first condition and
inverting the logic of the early return.

This changes the reading logic slightly. Before, the goto would exit the
function right away with the output of missed events. The next read would
then update print the saved hiter->dev and update it.

Now, in one iteration, if count_overruns() retruns !0, the lost events is
printed as well as the next hiter->dev without needing a second loop.

Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
Changes since v1: https://patch.msgid.link/20260721212010.76e9ed61@gandalf.local.home

- Broke it up into two patches

 kernel/trace/trace_mmiotrace.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/kernel/trace/trace_mmiotrace.c b/kernel/trace/trace_mmiotrace.c
index 0034d6af3d9d..c49738cdb439 100644
--- a/kernel/trace/trace_mmiotrace.c
+++ b/kernel/trace/trace_mmiotrace.c
@@ -143,16 +143,13 @@ static ssize_t mmio_read(struct trace_iterator *iter, struct file *filp,
 		if (!overrun_detected)
 			pr_warn("mmiotrace has lost events\n");
 		overrun_detected = true;
-		goto print_out;
 	}
 
-	if (!hiter || !hiter->dev)
-		return 0;
-
-	mmio_print_pcidev(s, hiter->dev);
-	hiter->dev = pci_get_device(PCI_ANY_ID, PCI_ANY_ID, hiter->dev);
+	if (hiter && hiter->dev) {
+		mmio_print_pcidev(s, hiter->dev);
+		hiter->dev = pci_get_device(PCI_ANY_ID, PCI_ANY_ID, hiter->dev);
+	}
 
-print_out:
 	ret = trace_seq_to_user(s, ubuf, cnt);
 	return (ret == -EBUSY) ? 0 : ret;
 }
-- 
2.53.0