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SubjectRe: kill -9 <pid of X>

Alan Cox writes:

> The bigger problems are that X11 is subject to being killed with sig 9
> (which with a horrible kernel hack can be blocked for iopl3 processes)

Is that so horrible? If X is going to bang hardware like kernel code,
it may as well act like kernel code.

> The related problems are SAK - which is defined to kill all processes
> on that VT and out of resource kills from the kernel (oom()). SAK is
> not that big a deal - a setuid "sak signal" ioctl akin to the way you
> take over console switching covers it.

Yes, as long as X won't let a user remap SAK.

> I'd agree however - you don't need to put all mode switching code in
> kernel if you allow iopl3 proceses to lock out sig 9 and you provide
> a sak hook. Oom should be solvable its just harder

Oom is easy: mlockall()

If X is going to play with hardware, then mlockall() is simply the
correct solution. X already disables interrupts sometimes. X can use
DMA too then, though a system call to get physical addresses would help.

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