Hello, On Sun, Jan 16, 2011 at 11:03:06PM -0500, John Stanley wrote: > The kernel-panic, which occurs at boot-time in udev/ata_id.c when > issuing an ioctl SG_IO sg3 SCSI ATA Pass-through Identify command, > appears to arise from DMA'ing into an incorrectly aligned user data > buffer pointed to by sg_io_hdr.dxferp . The problem is that nobody is DMA'ing in this case. The driver in question is ata_piix and the IO path taken is an actual PIO where the CPU reads from the IO space and writes to the memory itself. > My guess is that in the past, use of sg3 would not involve DMA by > default, but now, with libata ATA Pass-Through commands, it does (I > also may be totally wrong about that, just a thought). No DMA in progress here. The only (somewhat) recent related change would be libata PIO path now using 32bit IO commands when supported by the controller, but I fail to see how that would trigger this type of failures. > I recall documentaion somewhere which emphasized that if direct I/O > (DMA) is to used in sg, one should page-align the SCSI response data > buffer.. With sg using indirect I/O this wouldn't be necessary, of > course, but perhaps now with libata, it is. Just guessing here. If the buffer is not aligned, the kernel would just create a bounce buffer and bounce the data, so it shouldn't be a problem either. It looks like we have an obscure bug in buffer mapping code for SG_IO. I tried several things but can't reproduce the problem here. Can you please try the attached minimal test case? It issues IDENTIFY_PACKET and you can specify the alignment offset. By default the buffer would be 512byte aligned but you can offset it. ie. specifying 1 would make the buffer misaligned by 1 byte and so on. Can you please see whether the problem can be reliably triggered with it? Also, please, * Attach full kernel log (including boot messages) and the program output after triggering the problem. * Make sure the kernel is built with debug info and frame pointer. * Please reverse map the reported oops address to the source line. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-hotplug" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
