[Linaro-mm-sig] Re: [PATCH] dma-buf/sw_sync: Decrement refcount on error in sw_sync_ioctl_get_deadline()

On Mon, Mar 31, 2025 at 02:02:44PM +0200, Christian König wrote:

Am 31.03.25 um 11:45 schrieb Dan Carpenter:

...

Call dma_fence_put(fence) before returning an error on this error path.

Fixes: 70e67aaec2f4 ("dma-buf/sw_sync: Add fence deadline support") Signed-off-by: Dan Carpenter dan.carpenter@linaro.org

---

drivers/dma-buf/sw_sync.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/dma-buf/sw_sync.c b/drivers/dma-buf/sw_sync.c index f5905d67dedb..b7615c5c6cac 100644 --- a/drivers/dma-buf/sw_sync.c +++ b/drivers/dma-buf/sw_sync.c @@ -438,8 +438,10 @@ static int sw_sync_ioctl_get_deadline(struct sync_timeline *obj, unsigned long a return -EINVAL; pt = dma_fence_to_sync_pt(fence);

• if (!pt)

• if (!pt) {

• dma_fence_put(fence);
  

  return -EINVAL;
• }

Good catch.

I think it would be cleaner if we add an error label and then use "ret = -EINVAL; goto error;" here as well as a few lines below when ret is set to -ENOENT.

This way we can also avoid the ret = 0 in the declaration and let the compiler actually check the lifetime of the assignment.

I had some issues with my email and it silently ate a bunch of outgoing email without saving a single trace of anything I had sent. I see this was one that was eaten.

Unwind ladders don't work really well for things where you just take it for a little while and then drop it a few lines later. Such as here you take reference and then drop it or you take a lock and then drop it. Normally, you can add things to anywere in the unwind ladder but if you add an unlock to the ladder than you to add a weird bunny hop if the goto isn't holding the lock. It ends up getting confusing. With that kind of thing, I prefer to do the unlock before the goto.

free_c: free(c); goto free_b; <-- bunny hop; unlock: unlock(); free_b: free(b); free_a: free(a);

return ret;

regards, dan carpenter

diff --git a/drivers/dma-buf/sw_sync.c b/drivers/dma-buf/sw_sync.c index f5905d67dedb..22a808995f10 100644 --- a/drivers/dma-buf/sw_sync.c +++ b/drivers/dma-buf/sw_sync.c @@ -438,15 +438,17 @@ static int sw_sync_ioctl_get_deadline(struct sync_timeline *obj, unsigned long a return -EINVAL;

pt = dma_fence_to_sync_pt(fence); - if (!pt) - return -EINVAL; + if (!pt) { + ret = -EINVAL; + goto put_fence; + }

spin_lock_irqsave(fence->lock, flags); - if (test_bit(SW_SYNC_HAS_DEADLINE_BIT, &fence->flags)) { - data.deadline_ns = ktime_to_ns(pt->deadline); - } else { + if (!test_bit(SW_SYNC_HAS_DEADLINE_BIT, &fence->flags)) { ret = -ENOENT; + goto unlock; } + data.deadline_ns = ktime_to_ns(pt->deadline); spin_unlock_irqrestore(fence->lock, flags);

dma_fence_put(fence); @@ -458,6 +460,13 @@ static int sw_sync_ioctl_get_deadline(struct sync_timeline *obj, unsigned long a return -EFAULT;

return 0; + +unlock: + spin_unlock_irqrestore(fence->lock, flags); +put_fence: + dma_fence_put(fence); + + return ret; }

static long sw_sync_ioctl(struct file *file, unsigned int cmd,