Re: [PATCH v3 0/5] MIPS: Add per-cpu IRQ stack

Greg Kroah-Hartman
2017-01-15T13:48:37Z

On Sun, Jan 15, 2017 at 02:39:49PM +0100, Jason A. Donenfeld wrote:
> Hi James,
>
> On Fri, Jan 13, 2017 at 10:49 AM, James Hogan <james.hogan@imgtec.com> wrote:
> > Its quite a significant change/feature, especially in terms of potential
> > for further breakage. I don't think its really stable material to be
> > honest. It sounds bad if the kernel stack requirement can be made
> > arbitrarily large by stacking too many drivers.
>
> Indeed I believe this is the case. If, say, a kthread is already using
> a bit of stack, and then a softirq chain of stacked virtual network
> drivers is called, the stack can be busted.
>
> > Is there a simpler fix/workaround for the issue that would satisfy
> > stable kernel users until they can upgrade to a kernel with irqstacks?
>
> The simplest solution is probably just not stacking tons of network
> drivers. For my own out-of-tree curve25519-donna code that's in
> OpenWRT and uses a fair amount of stack, I just kmalloc on MIPS but
> not on x86, so in terms of my own stuff there's already a workaround
> in place. But this still doesn't solve things for users who have some
> interesting networking requirements and stack a few drivers.
>
> Unfortunately, most folks are only testing stuff on ARM and x86, which
> already have the separate IRQ stacks, so they aren't hitting crashes.
>
> So, in the end, I'm not quite sure. On the one hand, this fixes an
> actual problem and it'd be nice to see stable kernels have the fix. On
> the other hand, this is a rather big change. I don't know how to
> assess it, but I've copied Greg on this email, who certainly has
> better judgement about this than me.

How many patches is the irqstacks "feature" for MIPS? What kernel was
it released in? Have any git commit ids I can look at?

thanks,

greg k-h