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SubjectRe: Kexec, DMA, and SMP
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Eric W. Biederman wrote:

|Corey Minyard <cminyard@mvista.com> writes:
|
|>|
|>|(So adding a special mode to the power management code may
|>|be too much overhead. Besides, sometimes, you can just pull
|>|a reset line, and don't have to do anything even remotely
|>|related to power management.)
|>
|>True, I didn't mean the high-level power management code directly.
But the
|>PCI API defines a suspend operation that could take a special mode for
this.
|
|
|The generic device api has a shutdown method for this. And in the non
panic
|case we use it. Not a lot of devices have it implemented but it exists.
|
|And except that it doesn't have a restriction that it can't block is pretty
|much what you want.

That's a pretty big restriction. Plus, you can't claim spinlocks.

The panic shutdown is different from an orderly shutdown. What the
current shutdown does is probably not what you want.

|
|>Or maybe a new field in the PCI structure (and equivalent for other
things, if
|>there are any). But the suspend and resume operations should at least
give
|>a good idea where its needed and how to use it.
|
|
|The API is already done...

The API is not done for panics. There's no call that has the proper
semantics.

|
|
|We just don't trust the dying kernel enough to use it during a panic.

I don't understand this. If you can't trust a dying kernel to properly
shut down devices, how can you trust it to boot a new kernel? And (much
worse) if you don't shut down the devices, how can you trust the new
kernel to execute properly? I know there are levels of trust here, but
I'd much rather have the kernel lockup during the reboot than have a
chance of a new kernel booting that could behave incorrectly. In
general, the chance of behaving incorrectly is MUCH worse than a sure
lockup, especially in systems that must be reliable.

- -Corey
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