include/linux/percpu_counter.h: race in uniprocessor percpu_counter_a…

…dd()

The percpu interface is supposed to be preempt and irq safe.

But:
The uniprocessor implementation of percpu_counter_add() is not irq safe:
if an interrupt happens during the +=, then the result is undefined.

Therefore: switch from preempt_disable() to local_irq_save().
This prevents interrupts from interrupting the +=, and as a side effect
prevents preemption.

Link: https://lkml.kernel.org/r/20221216150441.200533-2-manfred@colorfullife.com
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Cc: "Sun, Jiebin" <jiebin.sun@intel.com>
Cc: <1vier1@web.de>
Cc: Alexander Sverdlin <alexander.sverdlin@siemens.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/percpu_counter.h

@@ -152,9 +152,11 @@ __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch)
 static inline void
 percpu_counter_add(struct percpu_counter *fbc, s64 amount)
 {
-	preempt_disable();
+	unsigned long flags;
+
+	local_irq_save(flags);
 	fbc->count += amount;
-	preempt_enable();
+	local_irq_restore(flags);
 }
 
 /* non-SMP percpu_counter_add_local is the same with percpu_counter_add */