| Message ID | 20210723075857.4065-1-michel@daenzer.net |
|---|---|
| State | New |
| Headers | show |
| Series | dma-buf/poll: Get a file reference for outstanding fence callbacks | expand |
Am 23.07.21 um 09:58 schrieb Michel Dänzer: > From: Michel Dänzer <mdaenzer@redhat.com> > > This makes sure we don't hit the > > BUG_ON(dmabuf->cb_in.active || dmabuf->cb_out.active); > > in dma_buf_release, which could be triggered by user space closing the > dma-buf file description while there are outstanding fence callbacks > from dma_buf_poll. I was also wondering the same thing while working on this, but then thought that the poll interface would take care of this. > > Cc: stable@vger.kernel.org > Signed-off-by: Michel Dänzer <mdaenzer@redhat.com> > --- > drivers/dma-buf/dma-buf.c | 18 ++++++++++++------ > 1 file changed, 12 insertions(+), 6 deletions(-) > > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c > index 6c520c9bd93c..ec25498a971f 100644 > --- a/drivers/dma-buf/dma-buf.c > +++ b/drivers/dma-buf/dma-buf.c > @@ -65,12 +65,9 @@ static void dma_buf_release(struct dentry *dentry) > BUG_ON(dmabuf->vmapping_counter); > > /* > - * Any fences that a dma-buf poll can wait on should be signaled > - * before releasing dma-buf. This is the responsibility of each > - * driver that uses the reservation objects. > - * > - * If you hit this BUG() it means someone dropped their ref to the > - * dma-buf while still having pending operation to the buffer. > + * If you hit this BUG() it could mean: > + * * There's a file reference imbalance in dma_buf_poll / dma_buf_poll_cb or somewhere else > + * * dmabuf->cb_in/out.active are non-0 despite no pending fence callback > */ > BUG_ON(dmabuf->cb_in.active || dmabuf->cb_out.active); > > @@ -196,6 +193,7 @@ static loff_t dma_buf_llseek(struct file *file, loff_t offset, int whence) > static void dma_buf_poll_cb(struct dma_fence *fence, struct dma_fence_cb *cb) > { > struct dma_buf_poll_cb_t *dcb = (struct dma_buf_poll_cb_t *)cb; > + struct dma_buf *dmabuf = container_of(dcb->poll, struct dma_buf, poll); > unsigned long flags; > > spin_lock_irqsave(&dcb->poll->lock, flags); > @@ -203,6 +201,8 @@ static void dma_buf_poll_cb(struct dma_fence *fence, struct dma_fence_cb *cb) > dcb->active = 0; > spin_unlock_irqrestore(&dcb->poll->lock, flags); > dma_fence_put(fence); > + /* Paired with get_file in dma_buf_poll */ > + fput(dmabuf->file); Is calling fput() in interrupt context ok? IIRC that could potentially sleep. Regards, Christian. > } > > static bool dma_buf_poll_shared(struct dma_resv *resv, > @@ -278,6 +278,9 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll) > spin_unlock_irq(&dmabuf->poll.lock); > > if (events & EPOLLOUT) { > + /* Paired with fput in dma_buf_poll_cb */ > + get_file(dmabuf->file); > + > if (!dma_buf_poll_shared(resv, dcb) && > !dma_buf_poll_excl(resv, dcb)) > /* No callback queued, wake up any other waiters */ > @@ -299,6 +302,9 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll) > spin_unlock_irq(&dmabuf->poll.lock); > > if (events & EPOLLIN) { > + /* Paired with fput in dma_buf_poll_cb */ > + get_file(dmabuf->file); > + > if (!dma_buf_poll_excl(resv, dcb)) > /* No callback queued, wake up any other waiters */ > dma_buf_poll_cb(NULL, &dcb->cb);
On 2021-07-23 10:04 a.m., Christian König wrote: > Am 23.07.21 um 09:58 schrieb Michel Dänzer: >> From: Michel Dänzer <mdaenzer@redhat.com> >> >> This makes sure we don't hit the >> >> BUG_ON(dmabuf->cb_in.active || dmabuf->cb_out.active); >> >> in dma_buf_release, which could be triggered by user space closing the >> dma-buf file description while there are outstanding fence callbacks >> from dma_buf_poll. > > I was also wondering the same thing while working on this, but then thought that the poll interface would take care of this. I was able to hit the BUG_ON with https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1880 . >> Cc: stable@vger.kernel.org >> Signed-off-by: Michel Dänzer <mdaenzer@redhat.com> >> --- >> drivers/dma-buf/dma-buf.c | 18 ++++++++++++------ >> 1 file changed, 12 insertions(+), 6 deletions(-) >> >> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c >> index 6c520c9bd93c..ec25498a971f 100644 >> --- a/drivers/dma-buf/dma-buf.c >> +++ b/drivers/dma-buf/dma-buf.c >> @@ -65,12 +65,9 @@ static void dma_buf_release(struct dentry *dentry) >> BUG_ON(dmabuf->vmapping_counter); >> /* >> - * Any fences that a dma-buf poll can wait on should be signaled >> - * before releasing dma-buf. This is the responsibility of each >> - * driver that uses the reservation objects. >> - * >> - * If you hit this BUG() it means someone dropped their ref to the >> - * dma-buf while still having pending operation to the buffer. >> + * If you hit this BUG() it could mean: >> + * * There's a file reference imbalance in dma_buf_poll / dma_buf_poll_cb or somewhere else >> + * * dmabuf->cb_in/out.active are non-0 despite no pending fence callback >> */ >> BUG_ON(dmabuf->cb_in.active || dmabuf->cb_out.active); >> @@ -196,6 +193,7 @@ static loff_t dma_buf_llseek(struct file *file, loff_t offset, int whence) >> static void dma_buf_poll_cb(struct dma_fence *fence, struct dma_fence_cb *cb) >> { >> struct dma_buf_poll_cb_t *dcb = (struct dma_buf_poll_cb_t *)cb; >> + struct dma_buf *dmabuf = container_of(dcb->poll, struct dma_buf, poll); >> unsigned long flags; >> spin_lock_irqsave(&dcb->poll->lock, flags); >> @@ -203,6 +201,8 @@ static void dma_buf_poll_cb(struct dma_fence *fence, struct dma_fence_cb *cb) >> dcb->active = 0; >> spin_unlock_irqrestore(&dcb->poll->lock, flags); >> dma_fence_put(fence); >> + /* Paired with get_file in dma_buf_poll */ >> + fput(dmabuf->file); > > Is calling fput() in interrupt context ok? IIRC that could potentially sleep. Looks fine AFAICT: It has if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) { and as a fallback for that, it adds the file to a lock-less delayed_fput_list which is processed by a workqueue.
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 6c520c9bd93c..ec25498a971f 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -65,12 +65,9 @@ static void dma_buf_release(struct dentry *dentry) BUG_ON(dmabuf->vmapping_counter); /* - * Any fences that a dma-buf poll can wait on should be signaled - * before releasing dma-buf. This is the responsibility of each - * driver that uses the reservation objects. - * - * If you hit this BUG() it means someone dropped their ref to the - * dma-buf while still having pending operation to the buffer. + * If you hit this BUG() it could mean: + * * There's a file reference imbalance in dma_buf_poll / dma_buf_poll_cb or somewhere else + * * dmabuf->cb_in/out.active are non-0 despite no pending fence callback */ BUG_ON(dmabuf->cb_in.active || dmabuf->cb_out.active); @@ -196,6 +193,7 @@ static loff_t dma_buf_llseek(struct file *file, loff_t offset, int whence) static void dma_buf_poll_cb(struct dma_fence *fence, struct dma_fence_cb *cb) { struct dma_buf_poll_cb_t *dcb = (struct dma_buf_poll_cb_t *)cb; + struct dma_buf *dmabuf = container_of(dcb->poll, struct dma_buf, poll); unsigned long flags; spin_lock_irqsave(&dcb->poll->lock, flags); @@ -203,6 +201,8 @@ static void dma_buf_poll_cb(struct dma_fence *fence, struct dma_fence_cb *cb) dcb->active = 0; spin_unlock_irqrestore(&dcb->poll->lock, flags); dma_fence_put(fence); + /* Paired with get_file in dma_buf_poll */ + fput(dmabuf->file); } static bool dma_buf_poll_shared(struct dma_resv *resv, @@ -278,6 +278,9 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll) spin_unlock_irq(&dmabuf->poll.lock); if (events & EPOLLOUT) { + /* Paired with fput in dma_buf_poll_cb */ + get_file(dmabuf->file); + if (!dma_buf_poll_shared(resv, dcb) && !dma_buf_poll_excl(resv, dcb)) /* No callback queued, wake up any other waiters */ @@ -299,6 +302,9 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll) spin_unlock_irq(&dmabuf->poll.lock); if (events & EPOLLIN) { + /* Paired with fput in dma_buf_poll_cb */ + get_file(dmabuf->file); + if (!dma_buf_poll_excl(resv, dcb)) /* No callback queued, wake up any other waiters */ dma_buf_poll_cb(NULL, &dcb->cb);