Re: [RFC PATCH 0/8] arm64: move thread_info off of the task stack

From: Mark Rutland
Date: Wed Sep 21 2016 - 06:32:15 EST

On Tue, Sep 20, 2016 at 06:26:54PM -0700, Laura Abbott wrote:
> On 09/15/2016 06:49 AM, Mark Rutland wrote:
> >Building atop of Andy's work on x86 and generic code, these patches move
> >arm64's thread_info off of the stack and into task_struct. This protects
> >thread_info from corruption in the face of stack overflow, and serves as
> >a step towards fully robust stack overflow handling will be addressed by
> >subsequent patches.
> >
> >In contrast to x86, we can't place some critical data such as
> >preempt_count in percpu variables, and we must store these in some
> >per-task location. This, compounded with the way headers are organised
> >conspires to require us to still define our own thread_info. I
> >understand that the longer term plan is to kill off thread_info
> >entirely, hence I'm sending this as an RFC so we can figure out if/how
> >we can achieve that.
> >
> >These patches are based on Andy's x86/vmap_stack branch [1,2], and I've
> >pushed a copy to me arm64/ti-stack-split branch [3,4]. The result of
> >these patches boots happily on platforms within reach of my desk, but
> >has not seen much stressing so far.
> FWIW, I used your ti-stack-split branch while running some kernel builds
> and it seems to work well enough. You can take that as a Tested-by or I
> can re-test with a non-RFC version.

Thanks for testing, and many thanks for the offer!

Based on Andy's feedback some core bits are changing, and I'm hoping to
have a non-RFC version out soon once I've fixed up the remaining
fallout. I'll make sure you're Cc'd!