staging: android: persistent_ram: make persistent_ram_write atomic

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/android/persistent_ram.c b/drivers/staging/android/persistent_ram.c
index 81950e6..3eb2fb4 100644 (file)
--- 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;
 }