ANDROID: ARM64: smp: disable preempt in backtracing across all cores

We use IPI instead of NMI in ARM64 to get backtrace of all CPUs.
However, smp_processor_id expects preempt disabled, and this leads to
a kernel BUG seen as below:

c3  19299 SysRq : Show backtrace of all active CPUs
c3  19299 BUG: using smp_processor_id() in preemptible [00000000] code: sh/19299
c3  19299 caller is debug_smp_processor_id+0x1c/0x24
c3  19299 CPU: 3 PID: 19299 Comm: sh Tainted: G        W      3.18.31-gb1be511 #1
c3  19299 Hardware name: HTC Corporation. MSM8996pro + PMI8996 Sailfish XB (DT)
c3  19299 Call trace:
c3  19299 [<ffffffc00008aab4>] dump_backtrace+0x0/0x23c
c3  19299 [<ffffffc00008ad04>] show_stack+0x14/0x1c
c3  19299 [<ffffffc000e29f38>] dump_stack+0x80/0xa4
c3  19299 [<ffffffc0003147a4>] check_preemption_disabled+0xe0/0x104
c3  19299 [<ffffffc0003147e4>] debug_smp_processor_id+0x1c/0x24
c3  19299 [<ffffffc000092b24>] arch_trigger_all_cpu_backtrace+0x18/0xdc
c3  19299 [<ffffffc00048dd64>] sysrq_handle_showallcpus+0xc/0x14
c3  19299 [<ffffffc00048e33c>] __handle_sysrq+0x9c/0x154
c3  19299 [<ffffffc00048e724>] write_sysrq_trigger+0x54/0x68
c3  19299 [<ffffffc0001f9c54>] proc_reg_write+0x68/0x84
c3  19299 [<ffffffc0001a6e0c>] vfs_write+0xbc/0x18c
c3  19299 [<ffffffc0001a6fd4>] SyS_write+0x54/0xa4
c3  19299 Backtrace for cpu 3 (current):
c3  19299 CPU: 3 PID: 19299 Comm: sh Tainted: G        W      3.18.31-gb1be511 #1
c3  19299 Hardware name: HTC Corporation. MSM8996pro + PMI8996 Sailfish XB (DT)
c3  19299 Call trace:
c3  19299 [<ffffffc00008aab4>] dump_backtrace+0x0/0x23c
c3  19299 [<ffffffc00008ad04>] show_stack+0x14/0x1c
c3  19299 [<ffffffc000e29f38>] dump_stack+0x80/0xa4
c3  19299 [<ffffffc000092b70>] arch_trigger_all_cpu_backtrace+0x64/0xdc
c3  19299 [<ffffffc00048dd64>] sysrq_handle_showallcpus+0xc/0x14
c3  19299 [<ffffffc00048e33c>] __handle_sysrq+0x9c/0x154
c3  19299 [<ffffffc00048e724>] write_sysrq_trigger+0x54/0x68
c3  19299 [<ffffffc0001f9c54>] proc_reg_write+0x68/0x84
c3  19299 [<ffffffc0001a6e0c>] vfs_write+0xbc/0x18c
c3  19299 [<ffffffc0001a6fd4>] SyS_write+0x54/0xa4
c3  19299
c3  19299 sending IPI to all other CPUs:
c3  19299 BUG: using smp_processor_id() in preemptible [00000000] code: sh/19299
c3  19299 caller is debug_smp_processor_id+0x1c/0x24
c3  19299 CPU: 3 PID: 19299 Comm: sh Tainted: G        W      3.18.31-gb1be511 #1
c3  19299 Hardware name: HTC Corporation. MSM8996pro + PMI8996 Sailfish XB (DT)
c3  19299 Call trace:
c3  19299 [<ffffffc00008aab4>] dump_backtrace+0x0/0x23c
c3  19299 [<ffffffc00008ad04>] show_stack+0x14/0x1c
c3  19299 [<ffffffc000e29f38>] dump_stack+0x80/0xa4
c3  19299 [<ffffffc0003147a4>] check_preemption_disabled+0xe0/0x104
c3  19299 [<ffffffc0003147e4>] debug_smp_processor_id+0x1c/0x24
c3  19299 [<ffffffc000327d24>] gic_raise_softirq+0x128/0x158
c3  19299 [<ffffffc000092828>] smp_cross_call_common+0x80/0x94
c3  19299 [<ffffffc000092b94>] arch_trigger_all_cpu_backtrace+0x88/0xdc
c3  19299 [<ffffffc00048dd64>] sysrq_handle_showallcpus+0xc/0x14
c3  19299 [<ffffffc00048e33c>] __handle_sysrq+0x9c/0x154
c3  19299 [<ffffffc00048e724>] write_sysrq_trigger+0x54/0x68
c3  19299 [<ffffffc0001f9c54>] proc_reg_write+0x68/0x84
c3  19299 [<ffffffc0001a6e0c>] vfs_write+0xbc/0x18c
c3  19299 [<ffffffc0001a6fd4>] SyS_write+0x54/0xa4

Bug: 35409577
Bug: 34193533
Test: on marlin, trigger sysrq
Change-Id: I0239f388c8ec63f10fc73a32bf8a7deddc408104
Signed-off-by: Wei Wang <[email protected]>
Signed-off-by: ahmedradaideh <[email protected]>

Author: weivincewang

arch/arm64/kernel/smp.c

@@ -617,15 +617,18 @@ static unsigned long backtrace_flag;
 
 static void smp_send_all_cpu_backtrace(void)
 {
-	unsigned int this_cpu = smp_processor_id();
+	unsigned int this_cpu;
 	int i;
 
-	if (test_and_set_bit(0, &backtrace_flag))
+	this_cpu = get_cpu();;
+	if (test_and_set_bit(0, &backtrace_flag)) {
 		/*
 		 * If there is already a trigger_all_cpu_backtrace() in progress
 		 * (backtrace_flag == 1), don't output double cpu dump infos.
 		 */
+		put_cpu();
 		return;
+	}
 
 	cpumask_copy(&backtrace_mask, cpu_online_mask);
 	cpu_clear(this_cpu, backtrace_mask);
@@ -637,6 +640,7 @@ static void smp_send_all_cpu_backtrace(void)
 	if (!cpus_empty(backtrace_mask))
 		smp_cross_call_common(&backtrace_mask, IPI_CPU_BACKTRACE);
 
+	put_cpu();
 	/* Wait for up to 10 seconds for all other CPUs to do the backtrace */
 	for (i = 0; i < 10 * 1000; i++) {
 		if (cpumask_empty(&backtrace_mask))