[PATCH v2 1/3] remoteproc: Fix unbalanced boot with sysfs for no auto-boot rprocs

[Suman Anna <s-anna@ti.com>]

The remoteproc core performs automatic boot and shutdown of a remote
processor during rproc_add() and rproc_del() for remote processors
supporting 'auto-boot'. The remoteproc devices not using 'auto-boot'
require either a remoteproc client driver or a userspace client to
use the sysfs 'state' variable to perform the boot and shutdown. The
in-kernel client drivers hold the corresponding remoteproc driver
module's reference count when they acquire a rproc handle through
the rproc_get_by_phandle() API, but there is no such support for
userspace applications performing the boot through sysfs interface.

The shutdown of a remoteproc upon removing a remoteproc platform
driver is automatic only with 'auto-boot' and this can cause a
remoteproc with no auto-boot to stay powered on and never freed
up if booted using the sysfs interface without a matching stop,
and when the remoteproc driver module is removed or unbound from
the device. This will result in a memory leak as well as the
corresponding remoteproc ida being never deallocated. Fix this
by holding a module reference count for the remoteproc's driver
during a sysfs 'start' and releasing it during the sysfs 'stop'
operation.

Signed-off-by: Suman Anna <s-anna@ti.com>
Acked-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
---
v2: rebased version, no changes
v1: https://patchwork.kernel.org/project/linux-remoteproc/patch/20180915003725.17549-2-s-anna@ti.com/

 drivers/remoteproc/remoteproc_sysfs.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/remoteproc/remoteproc_sysfs.c b/drivers/remoteproc/remoteproc_sysfs.c
index d1cf7bf277c4..bd2950a246c9 100644
--- a/drivers/remoteproc/remoteproc_sysfs.c
+++ b/drivers/remoteproc/remoteproc_sysfs.c
@@ -3,6 +3,7 @@
  * Remote Processor Framework
  */
 
+#include <linux/module.h>
 #include <linux/remoteproc.h>
 #include <linux/slab.h>
 
@@ -228,14 +229,27 @@ static ssize_t state_store(struct device *dev,
 		if (rproc->state == RPROC_RUNNING)
 			return -EBUSY;
 
+		/*
+		 * prevent underlying implementation from being removed
+		 * when remoteproc does not support auto-boot
+		 */
+		if (!rproc->auto_boot &&
+		    !try_module_get(dev->parent->driver->owner))
+			return -EINVAL;
+
 		ret = rproc_boot(rproc);
-		if (ret)
+		if (ret) {
 			dev_err(&rproc->dev, "Boot failed: %d\n", ret);
+			if (!rproc->auto_boot)
+				module_put(dev->parent->driver->owner);
+		}
 	} else if (sysfs_streq(buf, "stop")) {
 		if (rproc->state != RPROC_RUNNING)
 			return -EINVAL;
 
 		rproc_shutdown(rproc);
+		if (!rproc->auto_boot)
+			module_put(dev->parent->driver->owner);
 	} else {
 		dev_err(&rproc->dev, "Unrecognised option: %s\n", buf);
 		ret = -EINVAL;
-- 
2.28.0