[bug report] x86/split_lock: Make life miserable for split lockers

[Dan Carpenter <dan.carpenter@xxxxxxxxxx>]

Hello Tony Luck,

The patch b041b525dab9: "x86/split_lock: Make life miserable for
split lockers" from Mar 10, 2022 (linux-next), leads to the following
Smatch static checker warning:

	arch/x86/kernel/cpu/intel.c:1179 split_lock_warn()
	warn: sleeping in atomic context

arch/x86/kernel/cpu/intel.c
    1158 static void split_lock_warn(unsigned long ip)
    1159 {
    1160         struct delayed_work *work;
    1161         int cpu;
    1162 
    1163         if (!current->reported_split_lock)
    1164                 pr_warn_ratelimited("#AC: %s/%d took a split_lock trap at address: 0x%lx\n",
    1165                                     current->comm, current->pid, ip);
    1166         current->reported_split_lock = 1;
    1167 
    1168         if (sysctl_sld_mitigate) {
    1169                 /*
    1170                  * misery factor #1:
    1171                  * sleep 10ms before trying to execute split lock.
    1172                  */
    1173                 if (msleep_interruptible(10) > 0)
    1174                         return;
    1175                 /*
    1176                  * Misery factor #2:
    1177                  * only allow one buslocked disabled core at a time.
    1178                  */
--> 1179                 if (down_interruptible(&buslock_sem) == -EINTR)
    1180                         return;
    1181                 work = &sl_reenable_unlock;
    1182         } else {
    1183                 work = &sl_reenable;
    1184         }
    1185 
    1186         cpu = get_cpu();
    1187         schedule_delayed_work_on(cpu, work, 2);
    1188 
    1189         /* Disable split lock detection on this CPU to make progress */
    1190         sld_update_msr(false);
    1191         put_cpu();
    1192 }

The call tree is:

kernel_exc_vmm_communication() <- disables preempt
-> vc_raw_handle_exception()
   -> vc_forward_exception()
      -> exc_alignment_check()
         -> __exc_alignment_check()
            -> handle_user_split_lock()
               -> split_lock_warn()

I think maybe the mismatch is that kernel_exc_vmm_communication() calls
irqentry_nmi_enter(regs); which disable preemption but exc_alignment_check()
does local_irq_enable() which doesn't enable it.

Also why does arch/x86 not have a dedicated mailing list?

regards,
dan carpenter