ARM: entry: fix unwinder problems caused by IRQ stacks
The IRQ stacks series made some changes to the unwinder, to permit unwinding across different stacks. This is needed because otherwise, the call stack would terminate at the point where the stack switch between the task stack and the IRQ stack occurs, which would defeat any diagnostics that rely on timer interrupts, such as RCU stall detection. Unfortunately, getting the unwind annotations correct turns out to be difficult, given that this now involves a frame pointer which needs to point into the right location in the task stack when unwinding from the IRQ stack. Getting this wrong for an exception handling routine results in the stack pointer to be unwound from the wrong location, causing any subsequent unwind attempts to cause all kinds of issues, as reported by Naresh here [0]. So let's simplify this, by deferring the stack switch to call_with_stack(), which already has the correct unwind annotations, and removing all the complicated handling of the stack frame from the IRQ exception entrypoint itself. [0] https://lore.kernel.org/all/CA+G9fYtpy8VgK+ag6OsA9TDrwi5YGU4hu7GM8xwpO7v6LrCD4Q@mail.gmail.com/Signed-off-by:Ard Biesheuvel <ardb@kernel.org> Signed-off-by:
Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
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