kexec: Introduce kexec_with_frozen_processes

Drivers running .shutdown() might want to wait for userspace to complete
before exiting.

If userspace is frozen and we are running kexec they will stall the
computer.

Add a way for them to figure out if they should just skip waiting for
userspace.

Cc: stable@vger.kernel.org
Fixes: 83bfc7e ("ASoC: SOF: core: unregister clients and machine drivers in .shutdown")
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>

include/linux/kexec.h

@@ -426,6 +426,8 @@ extern int kexec_load_disabled;
 /* flag to track if kexec reboot is in progress */
 extern bool kexec_in_progress;
 
+bool kexec_with_frozen_processes(void);
+
 int crash_shrink_memory(unsigned long new_size);
 ssize_t crash_get_memory_size(void);
 
@@ -507,6 +509,7 @@ static inline void __crash_kexec(struct pt_regs *regs) { }
 static inline void crash_kexec(struct pt_regs *regs) { }
 static inline int kexec_should_crash(struct task_struct *p) { return 0; }
 static inline int kexec_crash_loaded(void) { return 0; }
+static inline bool kexec_with_frozen_processes(void) { return false; }
 #define kexec_in_progress false
 #endif /* CONFIG_KEXEC_CORE */
 

kernel/kexec_core.c

@@ -54,6 +54,11 @@ note_buf_t __percpu *crash_notes;
 /* Flag to indicate we are going to kexec a new kernel */
 bool kexec_in_progress = false;
 
+bool kexec_with_frozen_processes(void)
+{
+	return kexec_in_progress && pm_freezing;
+}
+EXPORT_SYMBOL(kexec_with_frozen_processes);
 
 /* Location of the reserved area for the crash kernel */
 struct resource crashk_res = {