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

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")
Cc: stable@vger.kernel.org
Acked-by: Arnd Bergmann <arnd@arndb.de> # asm-generic
Acked-by: Waiman Long <longman@redhat.com>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>
Link: https://lore.kernel.org/r/20260610090431.32427-1-gmonaco@redhat.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/include/asm-generic/rqspinlock.h b/include/asm-generic/rqspinlock.h
index 151d267a496b300c0d6107fd537d3807a2a05e46..4d46643f46cbc87139d65b1e42d1606c189be0a3 100644 (file)
--- 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 */