(replying to my own mail, apparently my normal outgoing email server is
blacklisted, so resending from @kernel.org)

On Fri, Oct 16, 2020 at 12:09 PM Arnd Bergmann [off-list ref] wrote:

On Thu, Oct 8, 2020 at 10:32 AM Russell King - ARM Linux admin
[off-list ref] wrote:

quoted

On Thu, Oct 08, 2020 at 12:45:30PM +0530, Maninder Singh wrote:

quoted

Observed Stack Overflow on 8KB kernel stack on ARM specially
incase on network interrupts, which results in undeterministic behaviour.
So there is need for per cpu dedicated IRQ stack for ARM.

As ARm does not have extra co-processor register
to save thread info pointer, IRQ stack will be at some
performance cost, so code is under CONFIG_IRQ_STACK.

and we don't have much knowledge and set up for CLANG
and ARM_UNWIND, so dependency added for both cases.

Tested patch set with QEMU for latest kernel
and 4.1 kernel for ARM target with same patch set.

You need to investigate and show where and why this is happening. My
guess is you have a network driver that uses a lot of kernel stack
space, which itself would be a bug.

Agreed.

quoted

Note that there are compiler versions out there that mis-optimise and
eat stack space - the kernel build should be warning if a function
uses a large amount of stack.

Some more ideas for figuring it out:

CONFIG_DEBUG_STACK_USAGE may also be helpful in identifying
code paths that are deeply nested with multiple functions taking a
lot of stack space, but each one staying under the limit.

CONFIG_DEBUG_STACKOVERFLOW would also help here but
is not supported on Arm at the moment. There was a patch[1] from
Uwe Kleine-König to add this, and I suppose we should still add
that, in particular if it helps debug this problem.

CONFIG_VMAP_STACK is probably the best way to debug
random runtime stack overflows because using a guard page
turns random memory corruption into an immediate oops,
but I don't think there is an implementation for Arm yet and
using a lot of vmalloc space means we might not be able to
default to this.

Regardless of identifying and fixing the bug Maninder found, I
also think that supporting separate async stacks on Arm is useful
for determinism. Most of the popular architectures use irqstack
for this reason, and I was actually surprised that we don't do it
on arch/arm/.

     Arnd

[1] https://lore.kernel.org/linux-arm-kernel/20200108082913.29710-1-u.kleine-koenig@pengutronix.de/ (local)

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