[PATCH 1/1] ARM: only call smp_send_stop() on SMP

[Russell King - ARM Linux]

See this thread:

http://lists.arm.linux.org.uk/lurker/thread/20120523.200015.2fdfd505.en.html

There are times when I wonder why I bother replying to email on mailing
lists.  No patch ever came from my responses on this subject.  Not going
to repeat it again.  Fed up.

On Sun, Jun 24, 2012 at 06:21:07AM +0200, Javier Martinez Canillas wrote:
> On reboot or poweroff (machine_shutdown()) a call to smp_send_stop() is
> made (to stop the others CPU's) when CONFIG_SMP=y.
> 
> arch/arm/kernel/process.c:
> 
> void machine_shutdown(void)
> {
>  #ifdef CONFIG_SMP
>        smp_send_stop();
>  #endif
> }
> 
> smp_send_stop() calls the function pointer smp_cross_call(), which is set
> on the smp_init_cpus() function for OMAP processors.
> 
> arch/arm/mach-omap2/omap-smp.c:
> 
> void __init smp_init_cpus(void)
> {
> ...
> 	set_smp_cross_call(gic_raise_softirq);
> ...
> }
> 
> But the ARM setup_arch() function only calls smp_init_cpus()
> if CONFIG_SMP=y && is_smp().
> 
> arm/kernel/setup.c:
> 
> void __init setup_arch(char **cmdline_p)
> {
> ...
>  #ifdef CONFIG_SMP
> 	if (is_smp())
> 		smp_init_cpus();
>  #endif
> ...
> }
> 
> Newer OMAP CPU's are SMP machines so omap2plus_defconfig sets
> CONFIG_SMP=y. Unfortunately on an OMAP UP machine is_smp()
> returns false and smp_init_cpus() is never called and the
> smp_cross_call() function remains NULL.
> 
> If the machine is rebooted or powered off, smp_send_stop() will
> be called (since CONFIG_SMP=y) leading to the following error:
> 
> [   42.815551] Restarting system.
> [   42.819030] Unable to handle kernel NULL pointer dereference at virtual address 00000000
> [   42.827667] pgd = d7a74000
> [   42.830566] [00000000] *pgd=96ce7831, *pte=00000000, *ppte=00000000
> [   42.837249] Internal error: Oops: 80000007 [#1] SMP ARM
> [   42.842773] Modules linked in:
> [   42.846008] CPU: 0    Not tainted  (3.5.0-rc3-next-20120622-00002-g62e87ba-dirty #44)
> [   42.854278] PC is at 0x0
> [   42.856994] LR is at smp_send_stop+0x4c/0xe4
> [   42.861511] pc : [<00000000>]    lr : [<c00183a4>]    psr: 60000013
> [   42.861511] sp : d6c85e70  ip : 00000000  fp : 00000000
> [   42.873626] r10: 00000000  r9 : d6c84000  r8 : 00000002
> [   42.879150] r7 : c07235a0  r6 : c06dd2d0  r5 : 000f4241  r4 : d6c85e74
> [   42.886047] r3 : 00000000  r2 : 00000000  r1 : 00000006  r0 : d6c85e74
> [   42.892944] Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment user
> [   42.900482] Control: 10c5387d  Table: 97a74019  DAC: 00000015
> [   42.906555] Process reboot (pid: 1166, stack limit = 0xd6c842f8)
> [   42.912902] Stack: (0xd6c85e70 to 0xd6c86000)
> [   42.917510] 5e60:                                     c07235a0 00000000 00000000 d6c84000
> [   42.926177] 5e80: 01234567 c00143d0 4321fedc c00511bc d6c85ebc 00000168 00000460 00000000
> [   42.934814] 5ea0: c1017950 a0000013 c1017900 d8014390 d7ec3858 c0498e48 c1017950 00000000
> [   42.943481] 5ec0: d6ddde10 d6c85f78 00000003 00000000 d6ddde10 d6c84000 00000000 00000000
> [   42.952117] 5ee0: 00000002 00000000 00000000 c0088c88 00000002 00000000 00000000 c00f4b90
> [   42.960784] 5f00: 00000000 d6c85ebc d8014390 d7e311c8 60000013 00000103 00000002 d6c84000
> [   42.969421] 5f20: c00f3274 d6e00a00 00000001 60000013 d6c84000 00000000 00000000 c00895d4
> [   42.978057] 5f40: 00000002 d8007c80 d781f000 c00f6150 d8010cc0 c00f3274 d781f000 d6c84000
> [   42.986694] 5f60: c0013020 d6e00a00 00000001 20000010 0001257c ef000000 00000000 c00895d4
> [   42.995361] 5f80: 00000002 00000001 00000003 00000000 00000001 00000003 00000000 00000058
> [   43.003997] 5fa0: c00130c8 c0012f00 00000001 00000003 fee1dead 28121969 01234567 00000002
> [   43.012634] 5fc0: 00000001 00000003 00000000 00000058 00012584 0001257c 00000001 00000000
> [   43.021270] 5fe0: 000124bc bec5cc6c 00008f9c 4a2f7c40 20000010 fee1dead 00000000 00000000
> [   43.029968] [<c00183a4>] (smp_send_stop+0x4c/0xe4) from [<c00143d0>] (machine_restart+0xc/0x4c)
> [   43.039154] [<c00143d0>] (machine_restart+0xc/0x4c) from [<c00511bc>] (sys_reboot+0x144/0x1f0)
> [   43.048278] [<c00511bc>] (sys_reboot+0x144/0x1f0) from [<c0012f00>] (ret_fast_syscall+0x0/0x3c)
> [   43.057464] Code: bad PC value
> [   43.060760] ---[ end trace c3988d1dd0b8f0fb ]---
> 
> An is_smp() check is also necessary besides shilding the smp_send_stop()
> call around CONFIG_SMP.
> 
> Signed-off-by: Javier Martinez Canillas <javier at dowhile0.org>
> ---
>  arch/arm/kernel/process.c |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
> index 864580a..a9043b8 100644
> --- a/arch/arm/kernel/process.c
> +++ b/arch/arm/kernel/process.c
> @@ -38,6 +38,7 @@
>  #include <asm/thread_notify.h>
>  #include <asm/stacktrace.h>
>  #include <asm/mach/time.h>
> +#include <asm/smp_plat.h>
>  
>  #ifdef CONFIG_CC_STACKPROTECTOR
>  #include <linux/stackprotector.h>
> @@ -240,7 +241,8 @@ __setup("reboot=", reboot_setup);
>  void machine_shutdown(void)
>  {
>  #ifdef CONFIG_SMP
> -	smp_send_stop();
> +	if (is_smp())
> +		smp_send_stop();
>  #endif
>  }
>  
> -- 
> 1.7.7.6
>