On Tue, 5 Oct 2021 at 14:23, Arnd Bergmann [off-list ref] wrote:

On Tue, Oct 5, 2021 at 9:15 AM Ard Biesheuvel [off-list ref] wrote:

quoted

Now that we have enabled IRQ stacks, any softIRQs that are handled over
the back of a hard IRQ will run from the IRQ stack as well. However, any
synchronous softirq processing that happens when re-enabling softIRQs
from task context will still execute on that task's stack.

So let's wire up the existing infrastructure to run these softIRQs from
the IRQ stack as well.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

The change looks reasonable, but maybe try to explain why it is
a good idea to do this.

Reviewed-by: Arnd Bergmann <arnd@arndb.de>

Sure. I will add something along the lines of

"""
Since any call to local_bh_enable() at any level in the task's call
stack may trigger a softIRQ processing run, which could potentially
cause a task stack overflow if the combined stack footprints exceed
the stack's size, let's run these synchronous invocations of
do_softirq() on the IRQ stack as well.
"""

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