On Apr 14, Alan Stern wrote: > On Mon, 14 Apr 2014, Ezequiel Garcia wrote: > > > Currently stk1160_read_reg() uses a stack-allocated char to get the > > read control value. This is wrong because usb_control_msg() requires > > a kmalloc-ed buffer, and a DMA-API warning is produced: > > > > WARNING: CPU: 0 PID: 1376 at lib/dma-debug.c:1153 check_for_stack+0xa0/0x100() > > ehci-pci 0000:00:0a.0: DMA-API: device driver maps memory fromstack [addr=ffff88003d0b56bf] > > > > This commit fixes such issue by using a 'usb_ctrl_read' field embedded > > in the device's struct to pass the value. In addition, we introduce a > > mutex to protect the value. > > This isn't right either. The buffer must be allocated in its own cache > line; it must not be part of a larger structure. > In that case, we can simply allocate 1 byte using kmalloc(). We won't be needing the mutex and it'll ensure proper cache alignment, right? -- Ezequiel García, Free Electrons Embedded Linux, Kernel and Android Engineering http://free-electrons.com -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
