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 <sm...@web.de>
Cc: sta...@vger.kernel.org # 3.14+
---
Cc: Mauro Carvalho Chehab <mche...@osg.samsung.com>
Cc: linux-media@vger.kernel.org
Cc: linux-ker...@vger.kernel.org
Since smp_store_release() and smp_load_acquire() were introduced in linux-3.14,
a 3.14+ stable tag was added. Is it desired to apply a similar patch to older
stable kernels?
---
drivers/media/dvb-core/dvb_ringbuffer.c | 27 ++++++++++++++-------------
1 file changed, 14 insertions(+), 13 deletions(-)
diff --git a/drivers/media/dvb-core/dvb_ringbuffer.c
b/drivers/media/dvb-core/dvb_ringbuffer.c
index 1100e98..58b5968 100644
--- a/drivers/media/dvb-core/dvb_ringbuffer.c
+++ b/drivers/media/dvb-core/dvb_ringbuffer.c
@@ -55,7 +55,7 @@ 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);
+ return (rbuf->pread == smp_load_acquire(&rbuf->pwrite));
}
@@ -64,7 +64,7 @@ ssize_t dvb_ringbuffer_free(struct dvb_ringbuffer *rbuf)
{
ssize_t free;
- free = rbuf->pread - rbuf->pwrite;
+ free = ACCESS_ONCE(rbuf->pread) - rbuf->pwrite;
if (free <= 0)
free += rbuf->size;
return free-1;
@@ -76,7 +76,7 @@ ssize_t dvb_ringbuffer_avail(struct dvb_ringbuffer *rbuf)
{
ssize_t avail;
- avail = rbuf->pwrite - rbuf->pread;
+ avail = smp_load_acquire(&rbuf->pwrite) - rbuf->pread;
if (avail < 0)
avail += rbuf->size;
return avail;
@@ -86,14 +86,15 @@ ssize_t dvb_ringbuffer_avail(struct dvb_ringbuffer *rbuf)
void dvb_ringbuffer_flush(struct dvb_ringbuffer *rbuf)
{
- rbuf->pread = rbuf->pwrite;
+ 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;
+ smp_store_release(&rbuf->pread, 0);
+ smp_store_release(&rbuf->pwrite, 0);
rbuf->error = 0;
}
@@ -119,12 +120,12 @@ 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(&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(&rbuf->pread, (rbuf->pread + todo) % rbuf->size);
return len;
}
@@ -139,11 +140,11 @@ 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(&rbuf->pread, 0);
}
memcpy(buf, rbuf->data+rbuf->pread, todo);
- rbuf->pread = (rbuf->pread + todo) % rbuf->size;
+ smp_store_release(&rbuf->pread, (rbuf->pread + todo) % rbuf->size);
}
@@ -158,10 +159,10 @@ 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(&rbuf->pwrite, 0);
}
memcpy(rbuf->data+rbuf->pwrite, buf, todo);
- rbuf->pwrite = (rbuf->pwrite + todo) % rbuf->size;
+ smp_store_release(&rbuf->pwrite, (rbuf->pwrite + todo) % rbuf->size);
return len;
}
@@ -181,12 +182,12 @@ ssize_t dvb_ringbuffer_write_user(struct dvb_ringbuffer
*rbuf,
return len - todo;
buf += split;
todo -= split;
- rbuf->pwrite = 0;
+ 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(&rbuf->pwrite, (rbuf->pwrite + todo) % rbuf->size);
return len;
}
--
1.9.1
--
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