Re: [RFC] DMA mapping error check analysis

From: Clemens Ladisch
Date: Mon Sep 10 2012 - 13:43:16 EST

Stefan Richter wrote:
> On Sep 10 Shuah Khan wrote:
>>>> File Name # of calls Status
>>>> drivers/firewire/core-iso.c 1 Unmap Broken
>>>> drivers/firewire/ohci.c 1 Unmap Broken
>>> In ohci.c, ar_context_release() takes care of cleanup.
>>> In core-iso.c, on failure, the callers are responsible to call
>>> fw_iso_buffer_destroy() eventually. (ioctl_create_iso_context()
>>> doesn't do this correctly if it's called multiple times.)
>> Thanks. I updated the page with your comments. I moved ohci.c to Good
>> status and left core-iso.c in Unmap Broken in case
>> ioctl_create_iso_context() case is worth fixing.
> I don't see what could go wrong if ioctl_create_iso_context() is called
> multiple times.

fw_iso_buffer_map_dma() maps as many pages as it can, and saves in
->page_count_mapped how many pages need unmapping.

When fw_iso_buffer_map_dma() fails, ioctl_create_iso_context() does _not_
call fw_iso_buffer_destroy() but takes care to not change the cdev's
state in any other way. So ioctl_create_iso_context() can be called
again and will then call fw_iso_buffer_map_dma(), which will happily
map the pages a second time, overwriting the previous mapped addresses.

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