module: Extend the preempt disabled section in dereference_symbol_descriptor().

dereference_symbol_descriptor() needs to obtain the module pointer
belonging to pointer in order to resolve that pointer.
The returned mod pointer is obtained under RCU-sched/ preempt_disable()
guarantees and needs to be used within this section to ensure that the
module is not removed in the meantime.

Extend the preempt_disable() section to also cover
dereference_module_function_descriptor().

Fixes: 04b8eb7 ("symbol lookup: introduce dereference_symbol_descriptor()")
Cc: James E.J. Bottomley <[email protected]>
Cc: Christophe Leroy <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: Madhavan Srinivasan <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Naveen N Rao <[email protected]>
Cc: Nicholas Piggin <[email protected]>
Cc: Sergey Senozhatsky <[email protected]>
Cc: [email protected]
Cc: [email protected]
Reviewed-by: Sergey Senozhatsky <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Pavlu <[email protected]>

Author: Sebastian Andrzej Siewior

include/linux/kallsyms.h

@@ -57,10 +57,10 @@ static inline void *dereference_symbol_descriptor(void *ptr)
 
 	preempt_disable();
 	mod = __module_address((unsigned long)ptr);
-	preempt_enable();
 
 	if (mod)
 		ptr = dereference_module_function_descriptor(mod, ptr);
+	preempt_enable();
 #endif
 	return ptr;
 }