[PATCH] rqspinlock: Fix order in raw_res_spin_(un)lock_irq to allow schedule

[Gabriele Monaco]

raw_res_spin_unlock_irqrestore() calls raw_res_spin_unlock() and then
restores interrupts, this means preemption is enabled when interrupts
are still disabled (as part of raw_res_spin_unlock()) so this cannot
trigger an actual preemption.
This is inconsistent with other spinlock implementations
(raw_spin_unlock_irqrestore() and bpf_res_spin_unlock_irqrestore()
itself).

Adjust the macro to ensure interrupts are enabled before enabling
preemption, allowing to schedule at that point. Make the same
modification in the error path of raw_res_spin_lock_irqsave().

Fixes: 101acd2e78b1 ("rqspinlock: Add macros for rqspinlock usage")
Signed-off-by: Gabriele Monaco <gmonaco@xxxxxxxxxx>
---
 include/asm-generic/rqspinlock.h | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/include/asm-generic/rqspinlock.h b/include/asm-generic/rqspinlock.h
index 151d267a49..4d46643f46 100644
--- a/include/asm-generic/rqspinlock.h
+++ b/include/asm-generic/rqspinlock.h
@@ -243,12 +243,20 @@ static __always_inline void res_spin_unlock(rqspinlock_t *lock)
 	({                                        \
 		int __ret;                        \
 		local_irq_save(flags);            \
-		__ret = raw_res_spin_lock(lock);  \
-		if (__ret)                        \
+		preempt_disable();                \
+		__ret = res_spin_lock(lock);      \
+		if (__ret) {                      \
 			local_irq_restore(flags); \
+			preempt_enable();         \
+		}                                 \
 		__ret;                            \
 	})
 
-#define raw_res_spin_unlock_irqrestore(lock, flags) ({ raw_res_spin_unlock(lock); local_irq_restore(flags); })
+#define raw_res_spin_unlock_irqrestore(lock, flags) \
+	({                                          \
+		res_spin_unlock(lock);              \
+		local_irq_restore(flags);           \
+		preempt_enable();                   \
+	})
 
 #endif /* __ASM_GENERIC_RQSPINLOCK_H */

base-commit: e43ffb69e0438cddd72aaa30898b4dc446f664f8
-- 
2.54.0