commit ca6e6126db5494f18c6c6615060d4d803b528bff upstream.
Implement memory barriers according to Documentation/circular-buffers.txt:
- use smp_store_release() to update ringbuffer read/write pointers
- use smp_load_acquire() to load write pointer on reader side
- use ACCESS_ONCE() to load read pointer on writer side
This fixes data stream corruptions observed e.g. on an ARM Cortex-A9
quad core system with different types (PCI, USB) of DVB tuners.
Signed-off-by: Soeren Moch <smoch@xxxxxx>
Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # 3.14.x .. 3.16.x
---
This is a backport for linux-stable 3.14.x and 3.16.x .
For 3.18+ the original patch can be used and already was applied for
4.4 and 4.7 .
---
drivers/media/dvb-core/dvb_ringbuffer.c | 64 +++++++++++++++++++++++++++------
1 file changed, 53 insertions(+), 11 deletions(-)
diff --git a/drivers/media/dvb-core/dvb_ringbuffer.c b/drivers/media/dvb-core/dvb_ringbuffer.c
index a5712cd..f29fc84 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;
}
--
1.9.1
--
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