4.7-stable review patch. If anyone has any objections, please let me know. ------------------ From: Matt Redfearn <matt.redfearn@xxxxxxxxxx> commit 8f46cca1e6c06a058374816887059bcc017b382f upstream. This patch fixes the possibility of a deadlock when bringing up secondary CPUs. The deadlock occurs because the set_cpu_online() is called before synchronise_count_slave(). This can cause a deadlock if the boot CPU, having scheduled another thread, attempts to send an IPI to the secondary CPU, which it sees has been marked online. The secondary is blocked in synchronise_count_slave() waiting for the boot CPU to enter synchronise_count_master(), but the boot cpu is blocked in smp_call_function_many() waiting for the secondary to respond to it's IPI request. Fix this by marking the CPU online in cpu_callin_map and synchronising counters before declaring the CPU online and calculating the maps for IPIs. Signed-off-by: Matt Redfearn <matt.redfearn@xxxxxxxxxx> Reported-by: Justin Chen <justinpopo6@xxxxxxxxx> Tested-by: Justin Chen <justinpopo6@xxxxxxxxx> Cc: Florian Fainelli <f.fainelli@xxxxxxxxx> Cc: linux-mips@xxxxxxxxxxxxxx Patchwork: https://patchwork.linux-mips.org/patch/14302/ Signed-off-by: Ralf Baechle <ralf@xxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/mips/kernel/smp.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) --- a/arch/mips/kernel/smp.c +++ b/arch/mips/kernel/smp.c @@ -320,6 +320,9 @@ asmlinkage void start_secondary(void) cpumask_set_cpu(cpu, &cpu_coherent_mask); notify_cpu_starting(cpu); + cpumask_set_cpu(cpu, &cpu_callin_map); + synchronise_count_slave(cpu); + set_cpu_online(cpu, true); set_cpu_sibling_map(cpu); @@ -327,10 +330,6 @@ asmlinkage void start_secondary(void) calculate_cpu_foreign_map(); - cpumask_set_cpu(cpu, &cpu_callin_map); - - synchronise_count_slave(cpu); - /* * irq will be enabled in ->smp_finish(), enabling it too early * is dangerous.
