CVE ID:	CVE-2021-47469
Description:	In the Linux kernel, the following vulnerability has been resolved: spi: Fix deadlock when adding SPI controllers on SPI buses Currently we have a global spi_add_lock which we take when adding new devices so that we can check that we're not trying to reuse a chip select that's already controlled. This means that if the SPI device is itself a SPI controller and triggers the instantiation of further SPI devices we trigger a deadlock as we try to register and instantiate those devices while in the process of doing so for the parent controller and hence already holding the global spi_add_lock. Since we only care about concurrency within a single SPI bus move the lock to be per controller, avoiding the deadlock. This can be easily triggered in the case of spi-mux.
Test IDs:	None available
Cross References:	Common Vulnerability Exposure (CVE) ID: CVE-2021-47469 https://git.kernel.org/stable/c/6098475d4cb48d821bdf453c61118c56e26294f0 https://git.kernel.org/stable/c/6098475d4cb48d821bdf453c61118c56e26294f0 https://git.kernel.org/stable/c/722ef19a161ce3fffb3d1b01ce2301c306639bdd https://git.kernel.org/stable/c/722ef19a161ce3fffb3d1b01ce2301c306639bdd