[PATCH] firmware_class: encapsulate firmware loading status

[Daniel Wagner]

From: Daniel Wagner <daniel.wagner@xxxxxxxxxxxx>

The firmware user helper code tracks the current state of the loading
process via an member of struct firmware_buf and a completion. Let's
encapsulate this simple state machine into struct fw_status. The aim is
to encrease readiblity and reduce the usage of the fw_lock.

The fw_lock is not needed to protect the status update anymore. We don't
do any RMW operations. Instead we just do a write or a read, not both at
the same time.

Signed-off-by: Daniel Wagner <daniel.wagner@xxxxxxxxxxxx>
Cc: Ming Lei <ming.lei@xxxxxxxxxxxxx>
Cc: Luis R. Rodriguez <mcgrof@xxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---

Hi,

In [0] we have a discussion on how the firmware_class API might be
changed to improve the current handling of firmware loading. This
patch was part of the orignal RFC which triggered the discussion.

I think it is worth taking this one anyway. Maybe as I suggested it
could be part of the series from Luis.

It cleans up the code base (okay my opinion) and removes the
complete_all() call which is problematic for -rt. complete_all() can
be used in any context including IRQ. That could lead to unbounded
work in the IRQ context and that is a no go for -rt. So here the
attempt to reduce the number of complete_all() calls where possible. I
have left this argument out in the commit message because I was told
'-rt' arguments don't count for inclusion.

cheers,
daniel

[0] http://www.spinics.net/lists/linux-wireless/msg153005.html

drivers/base/firmware_class.c | 148 ++++++++++++++++++++++++------------------
 1 file changed, 85 insertions(+), 63 deletions(-)

diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
index 773fc30..665a803 100644
--- a/drivers/base/firmware_class.c
+++ b/drivers/base/firmware_class.c
@@ -30,6 +30,7 @@
 #include <linux/syscore_ops.h>
 #include <linux/reboot.h>
 #include <linux/security.h>
+#include <linux/swait.h>
 
 #include <generated/utsrelease.h>
 
@@ -85,19 +86,78 @@ static inline bool fw_is_builtin_firmware(const struct firmware *fw)
 }
 #endif
 
+static int loading_timeout = 60;	/* In seconds */
+
+static inline long firmware_loading_timeout(void)
+{
+	return loading_timeout > 0 ? loading_timeout * HZ : MAX_JIFFY_OFFSET;
+}
+
 enum {
+	FW_STATUS_UNKNOWN,
 	FW_STATUS_LOADING,
 	FW_STATUS_DONE,
-	FW_STATUS_ABORT,
+	FW_STATUS_ABORTED,
 };
 
-static int loading_timeout = 60;	/* In seconds */
+struct fw_status {
+	unsigned long status;
+	struct swait_queue_head wq;
+};
 
-static inline long firmware_loading_timeout(void)
+
+static void fw_status_init(struct fw_status *fw_st)
 {
-	return loading_timeout > 0 ? loading_timeout * HZ : MAX_JIFFY_OFFSET;
+	fw_st->status = FW_STATUS_UNKNOWN;
+	init_swait_queue_head(&fw_st->wq);
+}
+
+static unsigned long __fw_status_get(struct fw_status *fw_st)
+{
+	return READ_ONCE(fw_st->status);
+}
+
+static inline bool is_fw_status_done(unsigned long status)
+{
+	return status == FW_STATUS_DONE ||
+	       status == FW_STATUS_ABORTED;
+}
+
+static int fw_status_wait_timeout(struct fw_status *fw_st, long timeout)
+{
+	int err;
+	err = swait_event_interruptible_timeout(fw_st->wq,
+				is_fw_status_done(READ_ONCE(fw_st->status)),
+				timeout);
+	if (err == 0 && fw_st->status == FW_STATUS_ABORTED)
+		return -ENOENT;
+
+	return err;
 }
 
+static void __fw_status_set(struct fw_status *fw_st,
+			  unsigned long status)
+{
+	WRITE_ONCE(fw_st->status, status);
+
+	if (status == FW_STATUS_DONE ||
+			status == FW_STATUS_ABORTED)
+		swake_up(&fw_st->wq);
+}
+
+#define fw_status_start(fw_st)					\
+	__fw_status_set(fw_st, FW_STATUS_LOADING)
+#define fw_status_done(fw_st)					\
+	__fw_status_set(fw_st, FW_STATUS_DONE)
+#define fw_status_aborted(fw_st)				\
+	__fw_status_set(fw_st, FW_STATUS_ABORTED)
+#define fw_status_is_loading(fw_st)				\
+	(__fw_status_get(fw_st) == FW_STATUS_LOADING)
+#define fw_status_is_done(fw_st)				\
+	(__fw_status_get(fw_st) == FW_STATUS_DONE)
+#define fw_status_is_aborted(fw_st)				\
+	(__fw_status_get(fw_st) == FW_STATUS_ABORTED)
+
 /* firmware behavior options */
 #define FW_OPT_UEVENT	(1U << 0)
 #define FW_OPT_NOWAIT	(1U << 1)
@@ -138,9 +198,8 @@ struct firmware_cache {
 struct firmware_buf {
 	struct kref ref;
 	struct list_head list;
-	struct completion completion;
+	struct fw_status fw_st;
 	struct firmware_cache *fwc;
-	unsigned long status;
 	void *data;
 	size_t size;
 #ifdef CONFIG_FW_LOADER_USER_HELPER
@@ -194,7 +253,7 @@ static struct firmware_buf *__allocate_fw_buf(const char *fw_name,
 
 	kref_init(&buf->ref);
 	buf->fwc = fwc;
-	init_completion(&buf->completion);
+	fw_status_init(&buf->fw_st);
 #ifdef CONFIG_FW_LOADER_USER_HELPER
 	INIT_LIST_HEAD(&buf->pending_list);
 #endif
@@ -292,15 +351,6 @@ static const char * const fw_path[] = {
 module_param_string(path, fw_path_para, sizeof(fw_path_para), 0644);
 MODULE_PARM_DESC(path, "customized firmware image search path with a higher priority than default path");
 
-static void fw_finish_direct_load(struct device *device,
-				  struct firmware_buf *buf)
-{
-	mutex_lock(&fw_lock);
-	set_bit(FW_STATUS_DONE, &buf->status);
-	complete_all(&buf->completion);
-	mutex_unlock(&fw_lock);
-}
-
 static int fw_get_filesystem_firmware(struct device *device,
 				       struct firmware_buf *buf)
 {
@@ -339,7 +389,7 @@ static int fw_get_filesystem_firmware(struct device *device,
 		}
 		dev_dbg(device, "direct-loading %s\n", buf->fw_id);
 		buf->size = size;
-		fw_finish_direct_load(device, buf);
+		fw_status_done(&buf->fw_st);
 		break;
 	}
 	__putname(path);
@@ -457,12 +507,11 @@ static void __fw_load_abort(struct firmware_buf *buf)
 	 * There is a small window in which user can write to 'loading'
 	 * between loading done and disappearance of 'loading'
 	 */
-	if (test_bit(FW_STATUS_DONE, &buf->status))
+	if (fw_status_is_done(&buf->fw_st))
 		return;
 
 	list_del_init(&buf->pending_list);
-	set_bit(FW_STATUS_ABORT, &buf->status);
-	complete_all(&buf->completion);
+	fw_status_aborted(&buf->fw_st);
 }
 
 static void fw_load_abort(struct firmware_priv *fw_priv)
@@ -475,9 +524,6 @@ static void fw_load_abort(struct firmware_priv *fw_priv)
 	fw_priv->buf = NULL;
 }
 
-#define is_fw_load_aborted(buf)	\
-	test_bit(FW_STATUS_ABORT, &(buf)->status)
-
 static LIST_HEAD(pending_fw_head);
 
 /* reboot notifier for avoid deadlock with usermode_lock */
@@ -575,10 +621,8 @@ static ssize_t firmware_loading_show(struct device *dev,
 	struct firmware_priv *fw_priv = to_firmware_priv(dev);
 	int loading = 0;
 
-	mutex_lock(&fw_lock);
 	if (fw_priv->buf)
-		loading = test_bit(FW_STATUS_LOADING, &fw_priv->buf->status);
-	mutex_unlock(&fw_lock);
+		loading = fw_status_is_loading(&fw_priv->buf->fw_st);
 
 	return sprintf(buf, "%d\n", loading);
 }
@@ -632,23 +676,20 @@ static ssize_t firmware_loading_store(struct device *dev,
 	switch (loading) {
 	case 1:
 		/* discarding any previous partial load */
-		if (!test_bit(FW_STATUS_DONE, &fw_buf->status)) {
+		if (!fw_status_is_done(&fw_buf->fw_st)) {
 			for (i = 0; i < fw_buf->nr_pages; i++)
 				__free_page(fw_buf->pages[i]);
 			vfree(fw_buf->pages);
 			fw_buf->pages = NULL;
 			fw_buf->page_array_size = 0;
 			fw_buf->nr_pages = 0;
-			set_bit(FW_STATUS_LOADING, &fw_buf->status);
+			fw_status_start(&fw_buf->fw_st);
 		}
 		break;
 	case 0:
-		if (test_bit(FW_STATUS_LOADING, &fw_buf->status)) {
+		if (fw_status_is_loading(&fw_buf->fw_st)) {
 			int rc;
 
-			set_bit(FW_STATUS_DONE, &fw_buf->status);
-			clear_bit(FW_STATUS_LOADING, &fw_buf->status);
-
 			/*
 			 * Several loading requests may be pending on
 			 * one same firmware buf, so let all requests
@@ -670,10 +711,11 @@ static ssize_t firmware_loading_store(struct device *dev,
 			 */
 			list_del_init(&fw_buf->pending_list);
 			if (rc) {
-				set_bit(FW_STATUS_ABORT, &fw_buf->status);
+				fw_status_aborted(&fw_buf->fw_st);
 				written = rc;
+			} else {
+				fw_status_done(&fw_buf->fw_st);
 			}
-			complete_all(&fw_buf->completion);
 			break;
 		}
 		/* fallthrough */
@@ -681,7 +723,7 @@ static ssize_t firmware_loading_store(struct device *dev,
 		dev_err(dev, "%s: unexpected value (%d)\n", __func__, loading);
 		/* fallthrough */
 	case -1:
-		fw_load_abort(fw_priv);
+		fw_status_aborted(&fw_buf->fw_st);
 		break;
 	}
 out:
@@ -702,7 +744,7 @@ static ssize_t firmware_data_read(struct file *filp, struct kobject *kobj,
 
 	mutex_lock(&fw_lock);
 	buf = fw_priv->buf;
-	if (!buf || test_bit(FW_STATUS_DONE, &buf->status)) {
+	if (!buf || fw_status_is_done(&buf->fw_st)) {
 		ret_count = -ENODEV;
 		goto out;
 	}
@@ -799,7 +841,7 @@ static ssize_t firmware_data_write(struct file *filp, struct kobject *kobj,
 
 	mutex_lock(&fw_lock);
 	buf = fw_priv->buf;
-	if (!buf || test_bit(FW_STATUS_DONE, &buf->status)) {
+	if (!buf || fw_status_is_done(&buf->fw_st)) {
 		retval = -ENODEV;
 		goto out;
 	}
@@ -917,8 +959,7 @@ static int _request_firmware_load(struct firmware_priv *fw_priv,
 		timeout = MAX_JIFFY_OFFSET;
 	}
 
-	retval = wait_for_completion_interruptible_timeout(&buf->completion,
-			timeout);
+	retval = fw_status_wait_timeout(&buf->fw_st, timeout);
 	if (retval == -ERESTARTSYS || !retval) {
 		mutex_lock(&fw_lock);
 		fw_load_abort(fw_priv);
@@ -927,7 +968,7 @@ static int _request_firmware_load(struct firmware_priv *fw_priv,
 		retval = 0;
 	}
 
-	if (is_fw_load_aborted(buf))
+	if (fw_status_is_aborted(&buf->fw_st))
 		retval = -EAGAIN;
 	else if (!buf->data)
 		retval = -ENOMEM;
@@ -978,7 +1019,7 @@ fw_load_from_user_helper(struct firmware *firmware, const char *name,
 }
 
 /* No abort during direct loading */
-#define is_fw_load_aborted(buf) false
+#define fw_status_is_aborted(buf) false
 
 #ifdef CONFIG_PM_SLEEP
 static inline void kill_requests_without_uevent(void) { }
@@ -986,26 +1027,6 @@ static inline void kill_requests_without_uevent(void) { }
 
 #endif /* CONFIG_FW_LOADER_USER_HELPER */
 
-
-/* wait until the shared firmware_buf becomes ready (or error) */
-static int sync_cached_firmware_buf(struct firmware_buf *buf)
-{
-	int ret = 0;
-
-	mutex_lock(&fw_lock);
-	while (!test_bit(FW_STATUS_DONE, &buf->status)) {
-		if (is_fw_load_aborted(buf)) {
-			ret = -ENOENT;
-			break;
-		}
-		mutex_unlock(&fw_lock);
-		ret = wait_for_completion_interruptible(&buf->completion);
-		mutex_lock(&fw_lock);
-	}
-	mutex_unlock(&fw_lock);
-	return ret;
-}
-
 /* prepare firmware and firmware_buf structs;
  * return 0 if a firmware is already assigned, 1 if need to load one,
  * or a negative error code
@@ -1039,7 +1060,8 @@ _request_firmware_prepare(struct firmware **firmware_p, const char *name,
 	firmware->priv = buf;
 
 	if (ret > 0) {
-		ret = sync_cached_firmware_buf(buf);
+		ret = fw_status_wait_timeout(&buf->fw_st,
+					   firmware_loading_timeout());
 		if (!ret) {
 			fw_set_page_data(buf, firmware);
 			return 0; /* assigned */
@@ -1057,7 +1079,7 @@ static int assign_firmware_buf(struct firmware *fw, struct device *device,
 	struct firmware_buf *buf = fw->priv;
 
 	mutex_lock(&fw_lock);
-	if (!buf->size || is_fw_load_aborted(buf)) {
+	if (!buf->size || fw_status_is_aborted(&buf->fw_st)) {
 		mutex_unlock(&fw_lock);
 		return -ENOENT;
 	}
-- 
2.7.4