Date:	Fri, 12 Jun 2015 20:30:24 -0400
From:	Dan Streetman <ddstreet@...e.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Jani Nikula <jani.nikula@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"David S. Miller" <davem@...emloft.net>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Dan Streetman <ddstreet@...e.org>
Subject: [PATCH] module: add per-module param_lock

Add a "param_lock" mutex to each module, and update params.c to use
the correct built-in or module mutex while locking kernel params.
Remove the kparam_block_sysfs_r/w() macros, replace them with direct
calls to kernel_param_[un]lock(module).

The kernel param code currently uses a single mutex to protect
modification of any and all kernel params.  While this generally works,
there is one specific problem with it; a module callback function
cannot safely load another module, i.e. with request_module() or even
with indirect calls such as crypto_has_alg().  If the module to be
loaded has any of its params configured (e.g. with a /etc/modprobe.d/*
config file), then the attempt will result in a deadlock between the
first module param callback waiting for modprobe, and modprobe trying to
lock the single kernel param mutex to set the new module's param.

This fixes that by using per-module mutexes, so that each individual module
is protected against concurrent changes in its own kernel params, but is
not blocked by changes to other module params.  All built-in modules
continue to use the built-in mutex, since they will always be loaded at
runtime and references (e.g. request_module(), crypto_has_alg()) to them
will never cause load-time param changing.

This also simplifies the interface used by modules to block sysfs access
to their params; while there are currently functions to block and unblock
sysfs param access which are split up by read and write and expect a single
kernel param to be passed, their actual operation is identical and applies
to all params, not just the one passed to them; they simply lock and unlock
the global param mutex.  They are replaced with direct calls to
kernel_param_[un]lock(THIS_MODULE), which locks THIS_MODULE's param_lock, or
if the module is built-in, it locks the built-in mutex.

Suggested-by: Rusty Russell <rusty@...tcorp.com.au>
Signed-off-by: Dan Streetman <ddstreet@...e.org>
---
You suggested giving direct access to the mutex, but this patch just
provides lock/unlock functions to the appropriate mutex, which seemed
cleaner and clearer to me, but if you prefer the direct mutex access
I can update the patch for that.

Also, this combines the making the kparam_lock into a per-module mutex,
with also removing the kparam_block_sysfs_*() macros; I can split that up
if you would prefer two patches.

 arch/um/drivers/hostaudio_kern.c                 | 20 ++++----
 drivers/net/ethernet/myricom/myri10ge/myri10ge.c |  6 +--
 drivers/net/wireless/libertas_tf/if_usb.c        |  6 +--
 drivers/usb/atm/ueagle-atm.c                     |  4 +-
 drivers/video/fbdev/vt8623fb.c                   |  4 +-
 include/linux/module.h                           |  1 +
 include/linux/moduleparam.h                      | 63 ++++--------------------
 kernel/module.c                                  |  2 +
 kernel/params.c                                  | 58 +++++++++++++---------
 net/mac80211/rate.c                              |  4 +-
 10 files changed, 69 insertions(+), 99 deletions(-)

diff --git a/arch/um/drivers/hostaudio_kern.c b/arch/um/drivers/hostaudio_kern.c
index 9b90fdc..f6b911c 100644
--- a/arch/um/drivers/hostaudio_kern.c
+++ b/arch/um/drivers/hostaudio_kern.c
@@ -185,9 +185,9 @@ static int hostaudio_open(struct inode *inode, struct file *file)
 	int ret;
 
 #ifdef DEBUG
-	kparam_block_sysfs_write(dsp);
+	kernel_param_lock(THIS_MODULE);
 	printk(KERN_DEBUG "hostaudio: open called (host: %s)\n", dsp);
-	kparam_unblock_sysfs_write(dsp);
+	kernel_param_unlock(THIS_MODULE);
 #endif
 
 	state = kmalloc(sizeof(struct hostaudio_state), GFP_KERNEL);
@@ -199,11 +199,11 @@ static int hostaudio_open(struct inode *inode, struct file *file)
 	if (file->f_mode & FMODE_WRITE)
 		w = 1;
 
-	kparam_block_sysfs_write(dsp);
+	kernel_param_lock(THIS_MODULE);
 	mutex_lock(&hostaudio_mutex);
 	ret = os_open_file(dsp, of_set_rw(OPENFLAGS(), r, w), 0);
 	mutex_unlock(&hostaudio_mutex);
-	kparam_unblock_sysfs_write(dsp);
+	kernel_param_unlock(THIS_MODULE);
 
 	if (ret < 0) {
 		kfree(state);
@@ -260,17 +260,17 @@ static int hostmixer_open_mixdev(struct inode *inode, struct file *file)
 	if (file->f_mode & FMODE_WRITE)
 		w = 1;
 
-	kparam_block_sysfs_write(mixer);
+	kernel_param_lock(THIS_MODULE);
 	mutex_lock(&hostaudio_mutex);
 	ret = os_open_file(mixer, of_set_rw(OPENFLAGS(), r, w), 0);
 	mutex_unlock(&hostaudio_mutex);
-	kparam_unblock_sysfs_write(mixer);
+	kernel_param_unlock(THIS_MODULE);
 
 	if (ret < 0) {
-		kparam_block_sysfs_write(dsp);
+		kernel_param_lock(THIS_MODULE);
 		printk(KERN_ERR "hostaudio_open_mixdev failed to open '%s', "
 		       "err = %d\n", dsp, -ret);
-		kparam_unblock_sysfs_write(dsp);
+		kernel_param_unlock(THIS_MODULE);
 		kfree(state);
 		return ret;
 	}
@@ -326,10 +326,10 @@ MODULE_LICENSE("GPL");
 
 static int __init hostaudio_init_module(void)
 {
-	__kernel_param_lock();
+	kernel_param_lock(THIS_MODULE);
 	printk(KERN_INFO "UML Audio Relay (host dsp = %s, host mixer = %s)\n",
 	       dsp, mixer);
-	__kernel_param_unlock();
+	kernel_param_unlock(THIS_MODULE);
 
 	module_data.dev_audio = register_sound_dsp(&hostaudio_fops, -1);
 	if (module_data.dev_audio < 0) {
diff --git a/drivers/net/ethernet/myricom/myri10ge/myri10ge.c b/drivers/net/ethernet/myricom/myri10ge/myri10ge.c
index 2bae502..83651ac 100644
--- a/drivers/net/ethernet/myricom/myri10ge/myri10ge.c
+++ b/drivers/net/ethernet/myricom/myri10ge/myri10ge.c
@@ -279,7 +279,7 @@ MODULE_FIRMWARE("myri10ge_eth_z8e.dat");
 MODULE_FIRMWARE("myri10ge_rss_ethp_z8e.dat");
 MODULE_FIRMWARE("myri10ge_rss_eth_z8e.dat");
 
-/* Careful: must be accessed under kparam_block_sysfs_write */
+/* Careful: must be accessed under kernel_param_lock() */
 static char *myri10ge_fw_name = NULL;
 module_param(myri10ge_fw_name, charp, S_IRUGO | S_IWUSR);
 MODULE_PARM_DESC(myri10ge_fw_name, "Firmware image name");
@@ -3427,7 +3427,7 @@ static void myri10ge_select_firmware(struct myri10ge_priv *mgp)
 		}
 	}
 
-	kparam_block_sysfs_write(myri10ge_fw_name);
+	kernel_param_lock(THIS_MODULE);
 	if (myri10ge_fw_name != NULL) {
 		char *fw_name = kstrdup(myri10ge_fw_name, GFP_KERNEL);
 		if (fw_name) {
@@ -3435,7 +3435,7 @@ static void myri10ge_select_firmware(struct myri10ge_priv *mgp)
 			set_fw_name(mgp, fw_name, true);
 		}
 	}
-	kparam_unblock_sysfs_write(myri10ge_fw_name);
+	kernel_param_unlock(THIS_MODULE);
 
 	if (mgp->board_number < MYRI10GE_MAX_BOARDS &&
 	    myri10ge_fw_names[mgp->board_number] != NULL &&
diff --git a/drivers/net/wireless/libertas_tf/if_usb.c b/drivers/net/wireless/libertas_tf/if_usb.c
index 1a20cee..799a2ef 100644
--- a/drivers/net/wireless/libertas_tf/if_usb.c
+++ b/drivers/net/wireless/libertas_tf/if_usb.c
@@ -821,15 +821,15 @@ static int if_usb_prog_firmware(struct if_usb_card *cardp)
 
 	lbtf_deb_enter(LBTF_DEB_USB);
 
-	kparam_block_sysfs_write(fw_name);
+	kernel_param_lock(THIS_MODULE);
 	ret = request_firmware(&cardp->fw, lbtf_fw_name, &cardp->udev->dev);
 	if (ret < 0) {
 		pr_err("request_firmware() failed with %#x\n", ret);
 		pr_err("firmware %s not found\n", lbtf_fw_name);
-		kparam_unblock_sysfs_write(fw_name);
+		kernel_param_unlock(THIS_MODULE);
 		goto done;
 	}
-	kparam_unblock_sysfs_write(fw_name);
+	kernel_param_unlock(THIS_MODULE);
 
 	if (check_fwfile_format(cardp->fw->data, cardp->fw->size))
 		goto release_fw;
diff --git a/drivers/usb/atm/ueagle-atm.c b/drivers/usb/atm/ueagle-atm.c
index 888998a..a2ae88d 100644
--- a/drivers/usb/atm/ueagle-atm.c
+++ b/drivers/usb/atm/ueagle-atm.c
@@ -1599,7 +1599,7 @@ static void cmvs_file_name(struct uea_softc *sc, char *const cmv_name, int ver)
 	char file_arr[] = "CMVxy.bin";
 	char *file;
 
-	kparam_block_sysfs_write(cmv_file);
+	kernel_param_lock(THIS_MODULE);
 	/* set proper name corresponding modem version and line type */
 	if (cmv_file[sc->modem_index] == NULL) {
 		if (UEA_CHIP_VERSION(sc) == ADI930)
@@ -1618,7 +1618,7 @@ static void cmvs_file_name(struct uea_softc *sc, char *const cmv_name, int ver)
 	strlcat(cmv_name, file, UEA_FW_NAME_MAX);
 	if (ver == 2)
 		strlcat(cmv_name, ".v2", UEA_FW_NAME_MAX);
-	kparam_unblock_sysfs_write(cmv_file);
+	kernel_param_unlock(THIS_MODULE);
 }
 
 static int request_cmvs_old(struct uea_softc *sc,
diff --git a/drivers/video/fbdev/vt8623fb.c b/drivers/video/fbdev/vt8623fb.c
index ea7f056..8bac309 100644
--- a/drivers/video/fbdev/vt8623fb.c
+++ b/drivers/video/fbdev/vt8623fb.c
@@ -754,9 +754,9 @@ static int vt8623_pci_probe(struct pci_dev *dev, const struct pci_device_id *id)
 
 	/* Prepare startup mode */
 
-	kparam_block_sysfs_write(mode_option);
+	kernel_param_lock(THIS_MODULE);
 	rc = fb_find_mode(&(info->var), info, mode_option, NULL, 0, NULL, 8);
-	kparam_unblock_sysfs_write(mode_option);
+	kernel_param_unlock(THIS_MODULE);
 	if (! ((rc == 1) || (rc == 2))) {
 		rc = -EINVAL;
 		dev_err(info->device, "mode %s not found\n", mode_option);
diff --git a/include/linux/module.h b/include/linux/module.h
index c883b86..e8c24d8 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -232,6 +232,7 @@ struct module {
 	unsigned int num_syms;
 
 	/* Kernel parameters. */
+	struct mutex param_lock;
 	struct kernel_param *kp;
 	unsigned int num_kp;
 
diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index 1c9effa..e108b5c 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -67,8 +67,9 @@ enum {
 
 struct kernel_param {
 	const char *name;
+	struct module *mod;
 	const struct kernel_param_ops *ops;
-	u16 perm;
+	const u16 perm;
 	s8 level;
 	u8 flags;
 	union {
@@ -108,7 +109,7 @@ struct kparam_array
  *
  * @perm is 0 if the the variable is not to appear in sysfs, or 0444
  * for world-readable, 0644 for root-writable, etc.  Note that if it
- * is writable, you may need to use kparam_block_sysfs_write() around
+ * is writable, you may need to use kernel_param_lock() around
  * accesses (esp. charp, which can be kfreed when it changes).
  *
  * The @type is simply pasted to refer to a param_ops_##type and a
@@ -216,12 +217,12 @@ struct kparam_array
    parameters. */
 #define __module_param_call(prefix, name, ops, arg, perm, level, flags)	\
 	/* Default value instead of permissions? */			\
-	static const char __param_str_##name[] = prefix #name; \
+	static const char __param_str_##name[] = prefix #name;		\
 	static struct kernel_param __moduleparam_const __param_##name	\
 	__used								\
     __attribute__ ((unused,__section__ ("__param"),aligned(sizeof(void *)))) \
-	= { __param_str_##name, ops, VERIFY_OCTAL_PERMISSIONS(perm),	\
-	    level, flags, { arg } }
+	= { __param_str_##name, THIS_MODULE, ops,			\
+	    VERIFY_OCTAL_PERMISSIONS(perm), level, flags, { arg } }
 
 /* Obsolete - use module_param_cb() */
 #define module_param_call(name, set, get, arg, perm)			\
@@ -238,58 +239,14 @@ __check_old_set_param(int (*oldset)(const char *, struct kernel_param *))
 	return 0;
 }
 
-/**
- * kparam_block_sysfs_write - make sure a parameter isn't written via sysfs.
- * @name: the name of the parameter
- *
- * There's no point blocking write on a paramter that isn't writable via sysfs!
- */
-#define kparam_block_sysfs_write(name)			\
-	do {						\
-		BUG_ON(!(__param_##name.perm & 0222));	\
-		__kernel_param_lock();			\
-	} while (0)
-
-/**
- * kparam_unblock_sysfs_write - allows sysfs to write to a parameter again.
- * @name: the name of the parameter
- */
-#define kparam_unblock_sysfs_write(name)		\
-	do {						\
-		BUG_ON(!(__param_##name.perm & 0222));	\
-		__kernel_param_unlock();		\
-	} while (0)
-
-/**
- * kparam_block_sysfs_read - make sure a parameter isn't read via sysfs.
- * @name: the name of the parameter
- *
- * This also blocks sysfs writes.
- */
-#define kparam_block_sysfs_read(name)			\
-	do {						\
-		BUG_ON(!(__param_##name.perm & 0444));	\
-		__kernel_param_lock();			\
-	} while (0)
-
-/**
- * kparam_unblock_sysfs_read - allows sysfs to read a parameter again.
- * @name: the name of the parameter
- */
-#define kparam_unblock_sysfs_read(name)			\
-	do {						\
-		BUG_ON(!(__param_##name.perm & 0444));	\
-		__kernel_param_unlock();		\
-	} while (0)
-
 #ifdef CONFIG_SYSFS
-extern void __kernel_param_lock(void);
-extern void __kernel_param_unlock(void);
+extern void kernel_param_lock(struct module *mod);
+extern void kernel_param_unlock(struct module *mod);
 #else
-static inline void __kernel_param_lock(void)
+static inline void kernel_param_lock(struct module *mod)
 {
 }
-static inline void __kernel_param_unlock(void)
+static inline void kernel_param_unlock(struct module *mod)
 {
 }
 #endif
diff --git a/kernel/module.c b/kernel/module.c
index cfc9e84..b8a684a 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3295,6 +3295,8 @@ static int load_module(struct load_info *info, const char __user *uargs,
 	if (err)
 		goto unlink_mod;
 
+	mutex_init(&mod->param_lock);
+
 	/* Now we've got everything in the final locations, we can
 	 * find optional sections. */
 	err = find_module_sections(mod, info);
diff --git a/kernel/params.c b/kernel/params.c
index a22d6a7..a27cead 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -25,15 +25,20 @@
 #include <linux/slab.h>
 #include <linux/ctype.h>
 
-/* Protects all parameters, and incidentally kmalloced_param list. */
+/* Protects all built-in parameters, modules use their own param_lock */
 static DEFINE_MUTEX(param_lock);
 
+/* Use the module's mutex, or if built-in use the built-in mutex */
+#define KPARAM_MUTEX(mod)	((mod) ? &(mod)->param_lock : &param_lock)
+#define KPARAM_IS_LOCKED(mod)	mutex_is_locked(KPARAM_MUTEX(mod))
+
 /* This just allows us to keep track of which parameters are kmalloced. */
 struct kmalloced_param {
 	struct list_head list;
 	char val[];
 };
 static LIST_HEAD(kmalloced_params);
+static DEFINE_SPINLOCK(kmalloced_params_lock);
 
 static void *kmalloc_parameter(unsigned int size)
 {
@@ -43,7 +48,10 @@ static void *kmalloc_parameter(unsigned int size)
 	if (!p)
 		return NULL;
 
+	spin_lock(&kmalloced_params_lock);
 	list_add(&p->list, &kmalloced_params);
+	spin_unlock(&kmalloced_params_lock);
+
 	return p->val;
 }
 
@@ -52,6 +60,7 @@ static void maybe_kfree_parameter(void *param)
 {
 	struct kmalloced_param *p;
 
+	spin_lock(&kmalloced_params_lock);
 	list_for_each_entry(p, &kmalloced_params, list) {
 		if (p->val == param) {
 			list_del(&p->list);
@@ -59,6 +68,7 @@ static void maybe_kfree_parameter(void *param)
 			break;
 		}
 	}
+	spin_unlock(&kmalloced_params_lock);
 }
 
 static char dash2underscore(char c)
@@ -118,10 +128,10 @@ static int parse_one(char *param,
 				return -EINVAL;
 			pr_debug("handling %s with %p\n", param,
 				params[i].ops->set);
-			mutex_lock(&param_lock);
+			kernel_param_lock(params[i].mod);
 			param_check_unsafe(&params[i]);
 			err = params[i].ops->set(val, &params[i]);
-			mutex_unlock(&param_lock);
+			kernel_param_unlock(params[i].mod);
 			return err;
 		}
 	}
@@ -364,12 +374,11 @@ EXPORT_SYMBOL(param_ops_invbool);
 
 int param_set_bint(const char *val, const struct kernel_param *kp)
 {
-	struct kernel_param boolkp;
+	/* Match bool exactly, by re-using it. */
+	struct kernel_param boolkp = *kp;
 	bool v;
 	int ret;
 
-	/* Match bool exactly, by re-using it. */
-	boolkp = *kp;
 	boolkp.arg = &v;
 
 	ret = param_set_bool(val, &boolkp);
@@ -387,7 +396,8 @@ struct kernel_param_ops param_ops_bint = {
 EXPORT_SYMBOL(param_ops_bint);
 
 /* We break the rule and mangle the string. */
-static int param_array(const char *name,
+static int param_array(struct module *mod,
+		       const char *name,
 		       const char *val,
 		       unsigned int min, unsigned int max,
 		       void *elem, int elemsize,
@@ -418,7 +428,7 @@ static int param_array(const char *name,
 		/* nul-terminate and parse */
 		save = val[len];
 		((char *)val)[len] = '\0';
-		BUG_ON(!mutex_is_locked(&param_lock));
+		BUG_ON(!KPARAM_IS_LOCKED(mod));
 		ret = set(val, &kp);
 
 		if (ret != 0)
@@ -440,7 +450,7 @@ static int param_array_set(const char *val, const struct kernel_param *kp)
 	const struct kparam_array *arr = kp->arr;
 	unsigned int temp_num;
 
-	return param_array(kp->name, val, 1, arr->max, arr->elem,
+	return param_array(kp->mod, kp->name, val, 1, arr->max, arr->elem,
 			   arr->elemsize, arr->ops->set, kp->level,
 			   arr->num ?: &temp_num);
 }
@@ -449,14 +459,13 @@ static int param_array_get(char *buffer, const struct kernel_param *kp)
 {
 	int i, off, ret;
 	const struct kparam_array *arr = kp->arr;
-	struct kernel_param p;
+	struct kernel_param p = *kp;
 
-	p = *kp;
 	for (i = off = 0; i < (arr->num ? *arr->num : arr->max); i++) {
 		if (i)
 			buffer[off++] = ',';
 		p.arg = arr->elem + arr->elemsize * i;
-		BUG_ON(!mutex_is_locked(&param_lock));
+		BUG_ON(!KPARAM_IS_LOCKED(p.mod));
 		ret = arr->ops->get(buffer + off, &p);
 		if (ret < 0)
 			return ret;
@@ -539,9 +548,9 @@ static ssize_t param_attr_show(struct module_attribute *mattr,
 	if (!attribute->param->ops->get)
 		return -EPERM;
 
-	mutex_lock(&param_lock);
+	kernel_param_lock(mk->mod);
 	count = attribute->param->ops->get(buf, attribute->param);
-	mutex_unlock(&param_lock);
+	kernel_param_unlock(mk->mod);
 	if (count > 0) {
 		strcat(buf, "\n");
 		++count;
@@ -551,7 +560,7 @@ static ssize_t param_attr_show(struct module_attribute *mattr,
 
 /* sysfs always hands a nul-terminated string in buf.  We rely on that. */
 static ssize_t param_attr_store(struct module_attribute *mattr,
-				struct module_kobject *km,
+				struct module_kobject *mk,
 				const char *buf, size_t len)
 {
  	int err;
@@ -560,10 +569,10 @@ static ssize_t param_attr_store(struct module_attribute *mattr,
 	if (!attribute->param->ops->set)
 		return -EPERM;
 
-	mutex_lock(&param_lock);
+	kernel_param_lock(mk->mod);
 	param_check_unsafe(attribute->param);
 	err = attribute->param->ops->set(buf, attribute->param);
-	mutex_unlock(&param_lock);
+	kernel_param_unlock(mk->mod);
 	if (!err)
 		return len;
 	return err;
@@ -576,18 +585,19 @@ static ssize_t param_attr_store(struct module_attribute *mattr,
 #define __modinit __init
 #endif
 
-#ifdef CONFIG_SYSFS
-void __kernel_param_lock(void)
+void kernel_param_lock(struct module *mod)
 {
-	mutex_lock(&param_lock);
+	mutex_lock(KPARAM_MUTEX(mod));
 }
-EXPORT_SYMBOL(__kernel_param_lock);
 
-void __kernel_param_unlock(void)
+void kernel_param_unlock(struct module *mod)
 {
-	mutex_unlock(&param_lock);
+	mutex_unlock(KPARAM_MUTEX(mod));
 }
-EXPORT_SYMBOL(__kernel_param_unlock);
+
+#ifdef CONFIG_SYSFS
+EXPORT_SYMBOL(kernel_param_lock);
+EXPORT_SYMBOL(kernel_param_unlock);
 
 /*
  * add_sysfs_param - add a parameter to sysfs
diff --git a/net/mac80211/rate.c b/net/mac80211/rate.c
index d53355b..8544e2e 100644
--- a/net/mac80211/rate.c
+++ b/net/mac80211/rate.c
@@ -103,7 +103,7 @@ ieee80211_rate_control_ops_get(const char *name)
 	const struct rate_control_ops *ops;
 	const char *alg_name;
 
-	kparam_block_sysfs_write(ieee80211_default_rc_algo);
+	kernel_param_lock(THIS_MODULE);
 	if (!name)
 		alg_name = ieee80211_default_rc_algo;
 	else
@@ -117,7 +117,7 @@ ieee80211_rate_control_ops_get(const char *name)
 	/* try built-in one if specific alg requested but not found */
 	if (!ops && strlen(CONFIG_MAC80211_RC_DEFAULT))
 		ops = ieee80211_try_rate_control_ops_get(CONFIG_MAC80211_RC_DEFAULT);
-	kparam_unblock_sysfs_write(ieee80211_default_rc_algo);
+	kernel_param_unlock(THIS_MODULE);
 
 	return ops;
 }
-- 
2.1.0

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