Re: [PATCH] ARM: integrator: Fix early initialization

[Guenter Roeck <linux@roeck-us.net>]

On 5/5/26 12:15, Linus Walleij wrote:
> From: Guenter Roeck <linux@roeck-us.net>
> 
> Starting with commit bdb249fce9ad4 ("ARM: integrator: read counter using
> syscon/regmap"), intcp_init_early calls syscon_regmap_lookup_by_compatible
> which in turn calls of_syscon_register. This function allocates memory.
> Since the memory management code has not been initialized at that time,
> the call always fails. It either returns -ENOMEM or crashes as follows.
> 
> Unable to handle kernel NULL pointer dereference at virtual address 0000000c when read
> [0000000c] *pgd=00000000
> Internal error: Oops: 5 [#1] ARM
> Modules linked in:
> CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 6.15.0-rc5-00026-g5fcc9bf84ee5 #1 PREEMPT
> Hardware name: ARM Integrator/CP (Device Tree)
> PC is at __kmalloc_cache_noprof+0xec/0x39c
> LR is at __kmalloc_cache_noprof+0x34/0x39c
> ...
> Call trace:
>   __kmalloc_cache_noprof from of_syscon_register+0x7c/0x310
>   of_syscon_register from device_node_get_regmap+0xa4/0xb0
>   device_node_get_regmap from intcp_init_early+0xc/0x40
>   intcp_init_early from start_kernel+0x60/0x688
>   start_kernel from 0x0
> 
> The crash is seen due to a dereferenced pointer which is not supposed to be
> NULL but is NULL if the memory management subsystem has not been
> initialized. The crash is not seen with all versions of gcc. Some versions
> such as gcc 9.x apparently do not dereference the pointer, presumably if
> tracing is disabled. The problem has been reproduced with gcc 10.x, 11.x,
> and 13.x. Either case, if the crash is not seen, the call to
> syscon_regmap_lookup_by_compatible returns -ENOMEM, and
> sched_clock_register is never called.
> 
> Fix the problem by moving the early initialization code into the standard
> machine initialization code.
> 
> Fixes: bdb249fce9ad4 ("ARM: integrator: read counter using syscon/regmap")
> Cc: Linus Walleij <linus.walleij@linaro.org>
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> Link: https://lore.kernel.org/20250518164118.3859567-1-linux@roeck-us.net
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
> ---
> Hi SoC folks, please apply this directly for fixes.
> Got stuck on a sideways branch for way too long.

I actually stopped testing the integratorcp qemu emulation
because it no longer works reliably, not even with gcc 9.x,
since the timer-sp804 patches were applied.

Given that apparently no one but me ever hit that problem,
I wonder if it is time to remove support for that machine entirely.

Guenter