pstore: Allow prz to control need for locking

BugLink: http://bugs.launchpad.net/bugs/1710646

commit 663deb47 upstream.

In preparation of not locking at all for certain buffers depending on if
there's contention, make locking optional depending on the initialization
of the prz.
Signed-off-by: Joel Fernandes <joelaf@google.com>
[kees: moved locking flag into prz instead of via caller arguments]
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

fs/pstore/ram.c

@@ -413,7 +413,7 @@ static int ramoops_init_przs(struct device *dev, struct ramoops_context *cxt,
 	for (i = 0; i < cxt->max_dump_cnt; i++) {
 		cxt->przs[i] = persistent_ram_new(*paddr, cxt->record_size, 0,
 						  &cxt->ecc_info,
-						  cxt->memtype);
+						  cxt->memtype, 0);
 		if (IS_ERR(cxt->przs[i])) {
 			err = PTR_ERR(cxt->przs[i]);
 			dev_err(dev, "failed to request mem region (0x%zx@0x%llx): %d\n",
@@ -450,7 +450,8 @@ static int ramoops_init_prz(struct device *dev, struct ramoops_context *cxt,
 		return -ENOMEM;
 	}
 
-	*prz = persistent_ram_new(*paddr, sz, sig, &cxt->ecc_info, cxt->memtype);
+	*prz = persistent_ram_new(*paddr, sz, sig, &cxt->ecc_info,
+				  cxt->memtype, 0);
 	if (IS_ERR(*prz)) {
 		int err = PTR_ERR(*prz);
 

fs/pstore/ram_core.c

@@ -52,9 +52,10 @@ static size_t buffer_start_add(struct persistent_ram_zone *prz, size_t a)
 {
 	int old;
 	int new;
-	unsigned long flags;
+	unsigned long flags = 0;
 
-	raw_spin_lock_irqsave(&prz->buffer_lock, flags);
+	if (!(prz->flags & PRZ_FLAG_NO_LOCK))
+		raw_spin_lock_irqsave(&prz->buffer_lock, flags);
 
 	old = atomic_read(&prz->buffer->start);
 	new = old + a;
@@ -62,7 +63,8 @@ static size_t buffer_start_add(struct persistent_ram_zone *prz, size_t a)
 		new -= prz->buffer_size;
 	atomic_set(&prz->buffer->start, new);
 
-	raw_spin_unlock_irqrestore(&prz->buffer_lock, flags);
+	if (!(prz->flags & PRZ_FLAG_NO_LOCK))
+		raw_spin_unlock_irqrestore(&prz->buffer_lock, flags);
 
 	return old;
 }
@@ -72,9 +74,10 @@ static void buffer_size_add(struct persistent_ram_zone *prz, size_t a)
 {
 	size_t old;
 	size_t new;
-	unsigned long flags;
+	unsigned long flags = 0;
 
-	raw_spin_lock_irqsave(&prz->buffer_lock, flags);
+	if (!(prz->flags & PRZ_FLAG_NO_LOCK))
+		raw_spin_lock_irqsave(&prz->buffer_lock, flags);
 
 	old = atomic_read(&prz->buffer->size);
 	if (old == prz->buffer_size)
@@ -86,7 +89,8 @@ static void buffer_size_add(struct persistent_ram_zone *prz, size_t a)
 	atomic_set(&prz->buffer->size, new);
 
 exit:
-	raw_spin_unlock_irqrestore(&prz->buffer_lock, flags);
+	if (!(prz->flags & PRZ_FLAG_NO_LOCK))
+		raw_spin_unlock_irqrestore(&prz->buffer_lock, flags);
 }
 
 static void notrace persistent_ram_encode_rs8(struct persistent_ram_zone *prz,
@@ -420,7 +424,8 @@ static int persistent_ram_buffer_map(phys_addr_t start, phys_addr_t size,
 }
 
 static int persistent_ram_post_init(struct persistent_ram_zone *prz, u32 sig,
-				    struct persistent_ram_ecc_info *ecc_info)
+				    struct persistent_ram_ecc_info *ecc_info,
+				    unsigned long flags)
 {
 	int ret;
 
@@ -449,6 +454,7 @@ static int persistent_ram_post_init(struct persistent_ram_zone *prz, u32 sig,
 	prz->buffer->sig = sig;
 	persistent_ram_zap(prz);
 	prz->buffer_lock = __RAW_SPIN_LOCK_UNLOCKED(buffer_lock);
+	prz->flags = flags;
 
 	return 0;
 }
@@ -473,7 +479,7 @@ void persistent_ram_free(struct persistent_ram_zone *prz)
 
 struct persistent_ram_zone *persistent_ram_new(phys_addr_t start, size_t size,
 			u32 sig, struct persistent_ram_ecc_info *ecc_info,
-			unsigned int memtype)
+			unsigned int memtype, u32 flags)
 {
 	struct persistent_ram_zone *prz;
 	int ret = -ENOMEM;
@@ -488,7 +494,7 @@ struct persistent_ram_zone *persistent_ram_new(phys_addr_t start, size_t size,
 	if (ret)
 		goto err;
 
-	ret = persistent_ram_post_init(prz, sig, ecc_info);
+	ret = persistent_ram_post_init(prz, sig, ecc_info, flags);
 	if (ret)
 		goto err;
 

include/linux/pstore_ram.h

@@ -23,6 +23,13 @@
 #include <linux/types.h>
 #include <linux/init.h>
 
+/*
+ * Choose whether access to the RAM zone requires locking or not.  If a zone
+ * can be written to from different CPUs like with ftrace for example, then
+ * PRZ_FLAG_NO_LOCK is used. For all other cases, locking is required.
+ */
+#define PRZ_FLAG_NO_LOCK	BIT(0)
+
 struct persistent_ram_buffer;
 struct rs_control;
 
@@ -39,6 +46,7 @@ struct persistent_ram_zone {
 	void *vaddr;
 	struct persistent_ram_buffer *buffer;
 	size_t buffer_size;
+	u32 flags;
 	raw_spinlock_t buffer_lock;
 
 	/* ECC correction */
@@ -55,7 +63,7 @@ struct persistent_ram_zone {
 
 struct persistent_ram_zone *persistent_ram_new(phys_addr_t start, size_t size,
 			u32 sig, struct persistent_ram_ecc_info *ecc_info,
-			unsigned int memtype);
+			unsigned int memtype, u32 flags);
 void persistent_ram_free(struct persistent_ram_zone *prz);
 void persistent_ram_zap(struct persistent_ram_zone *prz);