[PATCH 08/11] android: persistent_ram: make persistent_ram_write atomic

John Stultz
2012-03-08T01:36:34Z

From: Colin Cross <ccross@android.com>

Allow persistent_ram_write to be called on multiple cpus at
the same time, as long as ecc is not in use. Uses atomics
for the buffer->start and buffer->size counters.

[jstultz: Fix up some pr_info casting issues on 64bit]
CC: Greg KH <gregkh@linuxfoundation.org>
CC: Android Kernel Team <kernel-team@android.com>
Signed-off-by: Colin Cross <ccross@android.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
---
drivers/staging/android/persistent_ram.c | 140 +++++++++++++++++++++--------
1 files changed, 101 insertions(+), 39 deletions(-)

diff --git a/drivers/staging/android/persistent_ram.c b/drivers/staging/android/persistent_ram.c
index 81950e6..3eb2fb4 100644
--- a/drivers/staging/android/persistent_ram.c
+++ b/drivers/staging/android/persistent_ram.c
@@ -27,8 +27,8 @@

struct persistent_ram_buffer {
uint32_t sig;
- uint32_t start;
- uint32_t size;
+ atomic_t start;
+ atomic_t size;
uint8_t data[0];
};

@@ -36,6 +36,66 @@ struct persistent_ram_buffer {

static __initdata LIST_HEAD(persistent_ram_list);

+static inline size_t buffer_size(struct persistent_ram_zone *prz)
+{
+ return atomic_read(&prz->buffer->size);
+}
+
+static inline size_t buffer_start(struct persistent_ram_zone *prz)
+{
+ return atomic_read(&prz->buffer->start);
+}
+
+/* increase and wrap the start pointer, returning the old value */
+static inline size_t buffer_start_add(struct persistent_ram_zone *prz, size_t a)
+{
+ int old;
+ int new;
+
+ do {
+ old = atomic_read(&prz->buffer->start);
+ new = old + a;
+ while (unlikely(new > prz->buffer_size))
+ new -= prz->buffer_size;
+ } while (atomic_cmpxchg(&prz->buffer->start, old, new) != old);
+
+ return old;
+}
+
+/* increase the size counter until it hits the max size */
+static inline void buffer_size_add(struct persistent_ram_zone *prz, size_t a)
+{
+ size_t old;
+ size_t new;
+
+ if (atomic_read(&prz->buffer->size) == prz->buffer_size)
+ return;
+
+ do {
+ old = atomic_read(&prz->buffer->size);
+ new = old + a;
+ if (new > prz->buffer_size)
+ new = prz->buffer_size;
+ } while (atomic_cmpxchg(&prz->buffer->size, old, new) != old);
+}
+
+/* increase the size counter, retuning an error if it hits the max size */
+static inline ssize_t buffer_size_add_clamp(struct persistent_ram_zone *prz,
+ size_t a)
+{
+ size_t old;
+ size_t new;
+
+ do {
+ old = atomic_read(&prz->buffer->size);
+ new = old + a;
+ if (new > prz->buffer_size)
+ return -ENOMEM;
+ } while (atomic_cmpxchg(&prz->buffer->size, old, new) != old);
+
+ return 0;
+}
+
static void persistent_ram_encode_rs8(struct persistent_ram_zone *prz,
uint8_t *data, size_t len, uint8_t *ecc)
{
@@ -62,7 +122,7 @@ static int persistent_ram_decode_rs8(struct persistent_ram_zone *prz,
}

static void persistent_ram_update_ecc(struct persistent_ram_zone *prz,
- unsigned int count)
+ unsigned int start, unsigned int count)
{
struct persistent_ram_buffer *buffer = prz->buffer;
uint8_t *buffer_end = buffer->data + prz->buffer_size;
@@ -75,16 +135,16 @@ static void persistent_ram_update_ecc(struct persistent_ram_zone *prz,
if (!prz->ecc)
return;

- block = buffer->data + (buffer->start & ~(ecc_block_size - 1));
- par = prz->par_buffer +
- (buffer->start / ecc_block_size) * prz->ecc_size;
+ block = buffer->data + (start & ~(ecc_block_size - 1));
+ par = prz->par_buffer + (start / ecc_block_size) * prz->ecc_size;
+
do {
if (block + ecc_block_size > buffer_end)
size = buffer_end - block;
persistent_ram_encode_rs8(prz, block, size, par);
block += ecc_block_size;
par += ecc_size;
- } while (block < buffer->data + buffer->start + count);
+ } while (block < buffer->data + start + count);
}

static void persistent_ram_update_header_ecc(struct persistent_ram_zone *prz)
@@ -109,7 +169,7 @@ static void persistent_ram_ecc_old(struct persistent_ram_zone *prz)

block = buffer->data;
par = prz->par_buffer;
- while (block < buffer->data + buffer->size) {
+ while (block < buffer->data + buffer_size(prz)) {
int numerr;
int size = prz->ecc_block_size;
if (block + size > buffer->data + prz->buffer_size)
@@ -199,34 +259,33 @@ ssize_t persistent_ram_ecc_string(struct persistent_ram_zone *prz,
}

static void persistent_ram_update(struct persistent_ram_zone *prz,
- const void *s, unsigned int count)
+ const void *s, unsigned int start, unsigned int count)
{
struct persistent_ram_buffer *buffer = prz->buffer;
- memcpy(buffer->data + buffer->start, s, count);
- persistent_ram_update_ecc(prz, count);
+ memcpy(buffer->data + start, s, count);
+ persistent_ram_update_ecc(prz, start, count);
}

static void __init
persistent_ram_save_old(struct persistent_ram_zone *prz)
{
struct persistent_ram_buffer *buffer = prz->buffer;
- size_t old_log_size = buffer->size;
+ size_t size = buffer_size(prz);
+ size_t start = buffer_start(prz);
char *dest;

persistent_ram_ecc_old(prz);

- dest = kmalloc(old_log_size, GFP_KERNEL);
+ dest = kmalloc(size, GFP_KERNEL);
if (dest == NULL) {
pr_err("persistent_ram: failed to allocate buffer\n");
return;
}

prz->old_log = dest;
- prz->old_log_size = old_log_size;
- memcpy(prz->old_log,
- &buffer->data[buffer->start], buffer->size - buffer->start);
- memcpy(prz->old_log + buffer->size - buffer->start,
- &buffer->data[0], buffer->start);
+ prz->old_log_size = size;
+ memcpy(prz->old_log, &buffer->data[start], size - start);
+ memcpy(prz->old_log + size - start, &buffer->data[0], start);
}

int persistent_ram_write(struct persistent_ram_zone *prz,
@@ -234,25 +293,26 @@ int persistent_ram_write(struct persistent_ram_zone *prz,
{
int rem;
int c = count;
- struct persistent_ram_buffer *buffer = prz->buffer;
+ size_t start;

- if (c > prz->buffer_size) {
+ if (unlikely(c > prz->buffer_size)) {
s += c - prz->buffer_size;
c = prz->buffer_size;
}
- rem = prz->buffer_size - buffer->start;
- if (rem < c) {
- persistent_ram_update(prz, s, rem);
+
+ buffer_size_add_clamp(prz, c);
+
+ start = buffer_start_add(prz, c);
+
+ rem = prz->buffer_size - start;
+ if (unlikely(rem < c)) {
+ persistent_ram_update(prz, s, start, rem);
s += rem;
c -= rem;
- buffer->start = 0;
- buffer->size = prz->buffer_size;
+ start = 0;
}
- persistent_ram_update(prz, s, c);
+ persistent_ram_update(prz, s, start, c);

- buffer->start += c;
- if (buffer->size < prz->buffer_size)
- buffer->size += c;
persistent_ram_update_header_ecc(prz);

return count;
@@ -361,23 +421,25 @@ struct persistent_ram_zone *__persistent_ram_init(struct device *dev, bool ecc)
return ERR_PTR(ret);

if (prz->buffer->sig == PERSISTENT_RAM_SIG) {
- if (prz->buffer->size > prz->buffer_size
- || prz->buffer->start > prz->buffer->size)
- pr_info("persistent_ram: found existing invalid buffer, size %d, start %d\n",
- prz->buffer->size, prz->buffer->start);
+ if (buffer_size(prz) > prz->buffer_size ||
+ buffer_start(prz) > buffer_size(prz))
+ pr_info("persistent_ram: found existing invalid buffer,"
+ " size %ld, start %ld\n",
+ buffer_size(prz), buffer_start(prz));
else {
- pr_info("persistent_ram: found existing buffer, size %d, start %d\n",
- prz->buffer->size, prz->buffer->start);
+ pr_info("persistent_ram: found existing buffer,"
+ " size %ld, start %ld\n",
+ buffer_size(prz), buffer_start(prz));
persistent_ram_save_old(prz);
}
} else {
- pr_info("persistent_ram: no valid data in buffer (sig = 0x%08x)\n",
- prz->buffer->sig);
+ pr_info("persistent_ram: no valid data in buffer"
+ " (sig = 0x%08x)\n", prz->buffer->sig);
}

prz->buffer->sig = PERSISTENT_RAM_SIG;
- prz->buffer->start = 0;
- prz->buffer->size = 0;
+ atomic_set(&prz->buffer->start, 0);
+ atomic_set(&prz->buffer->size, 0);

return prz;
}
--
1.7.3.2.146.gca209