Re: Use of BQL from thread in PCIe device

[John Levon]

On Wed, Dec 18, 2024 at 04:19:47PM +0000, Markus Lavin wrote:

> Hi,
> 
> I think that I might have misunderstood something fundamental about the BQL
> (or possibly Qemu in general).
> 
> I have a custom PCIe device that connects to an outside simulation environment
> using Unix domain sockets. To deal with bus-mastering from this outside
> environment I have a thread created with qemu_thread_create listening to the
> socket.
> 
> If I get a read/write/interrupt request over the socket then the thread should
> perform a pci_dma_read/pci_dma_write/msix_notify. Since this is called from
> the threads context I assumed I should first grab the BQL. Issuing a bql_lock
> from the thread however hangs Qemu.
> 
> Is my thinking flawed?

The BQL will be already taken for these callbacks higher up in the stack I 
believe.

regards
john