Messages in this thread | | | Date | Thu, 29 Apr 1999 11:49:55 -0400 (EDT) | From | "Richard B. Johnson" <> | Subject | Re: Process VM Addr to Kernel VM Addr at Interrupt Time. |
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On Thu, 29 Apr 1999, Ramakrishna K wrote:
> > > Eric, > I have some question's. Excuse me for my ignorance. > > > I have written some code that does this properly. It properly locks pages, > > handles copy-on-write pages, and detects (and throws out, as it should) > > attempts to lock mmap'd or page cache memory. However, there is still a > > FATAL flaw in the code-- since the driver thread that locked the buffers > > runs in process context, if the process is killed while the driver is > > blocked awaiting DMA completion -- and the device is writing into user space > > -- the device can potentially be STILL DMA'ing into that memory after it has > > been free'd by the kernel, put into the page cache, allocated to a new > ^^^^^^^^^^^^^^^^^^^^ > > process, etc. > > Without a mechanism to allow the driver to be notified the process has died > > to stop the DMA disk buffers could be destroyed, processes overwritten, etc. > > This is a BAD THING.
Your device close function should handle this. When processes are killed, the kernel closes all file descriptors.
Cheers, Dick Johnson ***** FILE SYSTEM WAS MODIFIED ***** Penguin : Linux version 2.2.6 on an i686 machine (400.59 BogoMips). Warning : It's hard to remain at the trailing edge of technology.
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