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Subject[PATCH 3.18 34/92] pstore: Allow prz to control need for locking
Date
3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Joel Fernandes <joelaf@google.com>

commit 663deb47880f2283809669563c5a52ac7c6aef1a 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>

---
fs/pstore/ram.c | 5 +++--
fs/pstore/ram_core.c | 24 +++++++++++++++---------
include/linux/pstore_ram.h | 10 +++++++++-
3 files changed, 27 insertions(+), 12 deletions(-)

--- a/fs/pstore/ram.c
+++ b/fs/pstore/ram.c
@@ -365,7 +365,7 @@ static int ramoops_init_przs(struct devi

cxt->przs[i] = persistent_ram_new(*paddr, sz, 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",
@@ -395,7 +395,8 @@ static int ramoops_init_prz(struct devic
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);

--- a/fs/pstore/ram_core.c
+++ b/fs/pstore/ram_core.c
@@ -85,9 +85,10 @@ static size_t buffer_start_add_locked(st
{
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;
@@ -95,7 +96,8 @@ static size_t buffer_start_add_locked(st
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;
}
@@ -105,9 +107,10 @@ static void buffer_size_add_locked(struc
{
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)
@@ -119,7 +122,8 @@ static void buffer_size_add_locked(struc
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 size_t (*buffer_start_add)(struct persistent_ram_zone *, size_t) = buffer_start_add_atomic;
@@ -459,7 +463,8 @@ static int persistent_ram_buffer_map(phy
}

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;

@@ -488,6 +493,7 @@ static int persistent_ram_post_init(stru
prz->buffer->sig = sig;
persistent_ram_zap(prz);
prz->buffer_lock = __RAW_SPIN_LOCK_UNLOCKED(buffer_lock);
+ prz->flags = flags;

return 0;
}
@@ -512,7 +518,7 @@ void persistent_ram_free(struct persiste

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;
@@ -527,7 +533,7 @@ struct persistent_ram_zone *persistent_r
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;

--- a/include/linux/pstore_ram.h
+++ b/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);


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