[PATCH 1/1 v2] ARM: only call smp_send_stop() on SMP

[Shawn Guo]

It seems the same patch has been there for a while.

http://thread.gmane.org/gmane.linux.kernel/1303115

Regards,
Shawn

On Sun, Jun 24, 2012 at 12:28:10PM +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 ]---
> 
> Add a check so smp_cross_call() is only called when there is more than one CPU on-line.
> 
> Signed-off-by: Javier Martinez Canillas <javier at dowhile0.org>
> ---
> 
> Changes since v1:
> 
> - check for cpumask_empty() on arch/arm/kernel/smp.c instead for
>   is_smp() on arch/arm/kernel/process.c
> 
>  arch/arm/kernel/smp.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
> index 2c7217d..ea73045 100644
> --- a/arch/arm/kernel/smp.c
> +++ b/arch/arm/kernel/smp.c
> @@ -563,7 +563,8 @@ void smp_send_stop(void)
>  
>  	cpumask_copy(&mask, cpu_online_mask);
>  	cpumask_clear_cpu(smp_processor_id(), &mask);
> -	smp_cross_call(&mask, IPI_CPU_STOP);
> +	if (!cpumask_empty(&mask))
> +		smp_cross_call(&mask, IPI_CPU_STOP);
>  
>  	/* Wait up to one second for other CPUs to stop */
>  	timeout = USEC_PER_SEC;
> -- 
> 1.7.7.6
> 
> 
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