diff options
| -rw-r--r-- | drivers/media/dvb-core/dvb_ringbuffer.c | 74 |
1 files changed, 61 insertions, 13 deletions
diff --git a/drivers/media/dvb-core/dvb_ringbuffer.c b/drivers/media/dvb-core/dvb_ringbuffer.c index 1100e98a7b1d..7df7fb3738a0 100644 --- a/drivers/media/dvb-core/dvb_ringbuffer.c +++ b/drivers/media/dvb-core/dvb_ringbuffer.c @@ -55,7 +55,13 @@ void dvb_ringbuffer_init(struct dvb_ringbuffer *rbuf, void *data, size_t len) int dvb_ringbuffer_empty(struct dvb_ringbuffer *rbuf) { - return (rbuf->pread==rbuf->pwrite); + /* smp_load_acquire() to load write pointer on reader side + * this pairs with smp_store_release() in dvb_ringbuffer_write(), + * dvb_ringbuffer_write_user(), or dvb_ringbuffer_reset() + * + * for memory barriers also see Documentation/circular-buffers.txt + */ + return (rbuf->pread == smp_load_acquire(&rbuf->pwrite)); } @@ -64,7 +70,12 @@ ssize_t dvb_ringbuffer_free(struct dvb_ringbuffer *rbuf) { ssize_t free; - free = rbuf->pread - rbuf->pwrite; + /* ACCESS_ONCE() to load read pointer on writer side + * this pairs with smp_store_release() in dvb_ringbuffer_read(), + * dvb_ringbuffer_read_user(), dvb_ringbuffer_flush(), + * or dvb_ringbuffer_reset() + */ + free = ACCESS_ONCE(rbuf->pread) - rbuf->pwrite; if (free <= 0) free += rbuf->size; return free-1; @@ -76,7 +87,11 @@ ssize_t dvb_ringbuffer_avail(struct dvb_ringbuffer *rbuf) { ssize_t avail; - avail = rbuf->pwrite - rbuf->pread; + /* smp_load_acquire() to load write pointer on reader side + * this pairs with smp_store_release() in dvb_ringbuffer_write(), + * dvb_ringbuffer_write_user(), or dvb_ringbuffer_reset() + */ + avail = smp_load_acquire(&rbuf->pwrite) - rbuf->pread; if (avail < 0) avail += rbuf->size; return avail; @@ -86,14 +101,25 @@ ssize_t dvb_ringbuffer_avail(struct dvb_ringbuffer *rbuf) void dvb_ringbuffer_flush(struct dvb_ringbuffer *rbuf) { - rbuf->pread = rbuf->pwrite; + /* dvb_ringbuffer_flush() counts as read operation + * smp_load_acquire() to load write pointer + * smp_store_release() to update read pointer, this ensures that the + * correct pointer is visible for subsequent dvb_ringbuffer_free() + * calls on other cpu cores + */ + smp_store_release(&rbuf->pread, smp_load_acquire(&rbuf->pwrite)); rbuf->error = 0; } EXPORT_SYMBOL(dvb_ringbuffer_flush); void dvb_ringbuffer_reset(struct dvb_ringbuffer *rbuf) { - rbuf->pread = rbuf->pwrite = 0; + /* dvb_ringbuffer_reset() counts as read and write operation + * smp_store_release() to update read pointer + */ + smp_store_release(&rbuf->pread, 0); + /* smp_store_release() to update write pointer */ + smp_store_release(&rbuf->pwrite, 0); rbuf->error = 0; } @@ -119,12 +145,17 @@ ssize_t dvb_ringbuffer_read_user(struct dvb_ringbuffer *rbuf, u8 __user *buf, si return -EFAULT; buf += split; todo -= split; - rbuf->pread = 0; + /* smp_store_release() for read pointer update to ensure + * that buf is not overwritten until read is complete, + * this pairs with ACCESS_ONCE() in dvb_ringbuffer_free() + */ + smp_store_release(&rbuf->pread, 0); } if (copy_to_user(buf, rbuf->data+rbuf->pread, todo)) return -EFAULT; - rbuf->pread = (rbuf->pread + todo) % rbuf->size; + /* smp_store_release() to update read pointer, see above */ + smp_store_release(&rbuf->pread, (rbuf->pread + todo) % rbuf->size); return len; } @@ -139,11 +170,16 @@ void dvb_ringbuffer_read(struct dvb_ringbuffer *rbuf, u8 *buf, size_t len) memcpy(buf, rbuf->data+rbuf->pread, split); buf += split; todo -= split; - rbuf->pread = 0; + /* smp_store_release() for read pointer update to ensure + * that buf is not overwritten until read is complete, + * this pairs with ACCESS_ONCE() in dvb_ringbuffer_free() + */ + smp_store_release(&rbuf->pread, 0); } memcpy(buf, rbuf->data+rbuf->pread, todo); - rbuf->pread = (rbuf->pread + todo) % rbuf->size; + /* smp_store_release() to update read pointer, see above */ + smp_store_release(&rbuf->pread, (rbuf->pread + todo) % rbuf->size); } @@ -158,10 +194,16 @@ ssize_t dvb_ringbuffer_write(struct dvb_ringbuffer *rbuf, const u8 *buf, size_t memcpy(rbuf->data+rbuf->pwrite, buf, split); buf += split; todo -= split; - rbuf->pwrite = 0; + /* smp_store_release() for write pointer update to ensure that + * written data is visible on other cpu cores before the pointer + * update, this pairs with smp_load_acquire() in + * dvb_ringbuffer_empty() or dvb_ringbuffer_avail() + */ + smp_store_release(&rbuf->pwrite, 0); } memcpy(rbuf->data+rbuf->pwrite, buf, todo); - rbuf->pwrite = (rbuf->pwrite + todo) % rbuf->size; + /* smp_store_release() for write pointer update, see above */ + smp_store_release(&rbuf->pwrite, (rbuf->pwrite + todo) % rbuf->size); return len; } @@ -181,12 +223,18 @@ ssize_t dvb_ringbuffer_write_user(struct dvb_ringbuffer *rbuf, return len - todo; buf += split; todo -= split; - rbuf->pwrite = 0; + /* smp_store_release() for write pointer update to ensure that + * written data is visible on other cpu cores before the pointer + * update, this pairs with smp_load_acquire() in + * dvb_ringbuffer_empty() or dvb_ringbuffer_avail() + */ + smp_store_release(&rbuf->pwrite, 0); } status = copy_from_user(rbuf->data+rbuf->pwrite, buf, todo); if (status) return len - todo; - rbuf->pwrite = (rbuf->pwrite + todo) % rbuf->size; + /* smp_store_release() for write pointer update, see above */ + smp_store_release(&rbuf->pwrite, (rbuf->pwrite + todo) % rbuf->size); return len; } |