Commit ba59953d authored by Ben Skeggs's avatar Ben Skeggs
Browse files

drm/nouveau: fix a race condition in nouveau_dma_wait()



Can be triggered easily on certain cards (NV46 and NV50 of mine) by
running "dmesg", the DRM's channel will lockup.
Signed-off-by: default avatarBen Skeggs <bskeggs@redhat.com>
parent 12f735b7
......@@ -126,47 +126,52 @@ OUT_RINGp(struct nouveau_channel *chan, const void *data, unsigned nr_dwords)
chan->dma.cur += nr_dwords;
}
static inline bool
READ_GET(struct nouveau_channel *chan, uint32_t *get)
/* Fetch and adjust GPU GET pointer
*
* Returns:
* value >= 0, the adjusted GET pointer
* -EINVAL if GET pointer currently outside main push buffer
* -EBUSY if timeout exceeded
*/
static inline int
READ_GET(struct nouveau_channel *chan, uint32_t *prev_get, uint32_t *timeout)
{
uint32_t val;
val = nvchan_rd32(chan, chan->user_get);
if (val < chan->pushbuf_base ||
val > chan->pushbuf_base + (chan->dma.max << 2)) {
/* meaningless to dma_wait() except to know whether the
* GPU has stalled or not
*/
*get = val;
return false;
/* reset counter as long as GET is still advancing, this is
* to avoid misdetecting a GPU lockup if the GPU happens to
* just be processing an operation that takes a long time
*/
if (val != *prev_get) {
*prev_get = val;
*timeout = 0;
}
if ((++*timeout & 0xff) == 0) {
DRM_UDELAY(1);
if (*timeout > 100000)
return -EBUSY;
}
*get = (val - chan->pushbuf_base) >> 2;
return true;
if (val < chan->pushbuf_base ||
val > chan->pushbuf_base + (chan->dma.max << 2))
return -EINVAL;
return (val - chan->pushbuf_base) >> 2;
}
int
nouveau_dma_wait(struct nouveau_channel *chan, int size)
{
uint32_t get, prev_get = 0, cnt = 0;
bool get_valid;
uint32_t prev_get = 0, cnt = 0;
int get;
while (chan->dma.free < size) {
/* reset counter as long as GET is still advancing, this is
* to avoid misdetecting a GPU lockup if the GPU happens to
* just be processing an operation that takes a long time
*/
get_valid = READ_GET(chan, &get);
if (get != prev_get) {
prev_get = get;
cnt = 0;
}
if ((++cnt & 0xff) == 0) {
DRM_UDELAY(1);
if (cnt > 100000)
return -EBUSY;
}
get = READ_GET(chan, &prev_get, &cnt);
if (unlikely(get == -EBUSY))
return -EBUSY;
/* loop until we have a usable GET pointer. the value
* we read from the GPU may be outside the main ring if
......@@ -177,7 +182,7 @@ nouveau_dma_wait(struct nouveau_channel *chan, int size)
* from the SKIPS area, so the code below doesn't have to deal
* with some fun corner cases.
*/
if (!get_valid || get < NOUVEAU_DMA_SKIPS)
if (unlikely(get == -EINVAL) || get < NOUVEAU_DMA_SKIPS)
continue;
if (get <= chan->dma.cur) {
......@@ -203,6 +208,19 @@ nouveau_dma_wait(struct nouveau_channel *chan, int size)
* after processing the currently pending commands.
*/
OUT_RING(chan, chan->pushbuf_base | 0x20000000);
/* wait for GET to depart from the skips area.
* prevents writing GET==PUT and causing a race
* condition that causes us to think the GPU is
* idle when it's not.
*/
do {
get = READ_GET(chan, &prev_get, &cnt);
if (unlikely(get == -EBUSY))
return -EBUSY;
if (unlikely(get == -EINVAL))
continue;
} while (get <= NOUVEAU_DMA_SKIPS);
WRITE_PUT(NOUVEAU_DMA_SKIPS);
/* we're now submitting commands at the start of
......
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