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-rw-r--r--arch/x86/include/asm/rwsem.h237
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diff --git a/arch/x86/include/asm/rwsem.h b/arch/x86/include/asm/rwsem.h
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+++ b/arch/x86/include/asm/rwsem.h
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+/* SPDX-License-Identifier: GPL-2.0 */
+/* rwsem.h: R/W semaphores implemented using XADD/CMPXCHG for i486+
+ *
+ * Written by David Howells (dhowells@redhat.com).
+ *
+ * Derived from asm-x86/semaphore.h
+ *
+ *
+ * The MSW of the count is the negated number of active writers and waiting
+ * lockers, and the LSW is the total number of active locks
+ *
+ * The lock count is initialized to 0 (no active and no waiting lockers).
+ *
+ * When a writer subtracts WRITE_BIAS, it'll get 0xffff0001 for the case of an
+ * uncontended lock. This can be determined because XADD returns the old value.
+ * Readers increment by 1 and see a positive value when uncontended, negative
+ * if there are writers (and maybe) readers waiting (in which case it goes to
+ * sleep).
+ *
+ * The value of WAITING_BIAS supports up to 32766 waiting processes. This can
+ * be extended to 65534 by manually checking the whole MSW rather than relying
+ * on the S flag.
+ *
+ * The value of ACTIVE_BIAS supports up to 65535 active processes.
+ *
+ * This should be totally fair - if anything is waiting, a process that wants a
+ * lock will go to the back of the queue. When the currently active lock is
+ * released, if there's a writer at the front of the queue, then that and only
+ * that will be woken up; if there's a bunch of consecutive readers at the
+ * front, then they'll all be woken up, but no other readers will be.
+ */
+
+#ifndef _ASM_X86_RWSEM_H
+#define _ASM_X86_RWSEM_H
+
+#ifndef _LINUX_RWSEM_H
+#error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
+#endif
+
+#ifdef __KERNEL__
+#include <asm/asm.h>
+
+/*
+ * The bias values and the counter type limits the number of
+ * potential readers/writers to 32767 for 32 bits and 2147483647
+ * for 64 bits.
+ */
+
+#ifdef CONFIG_X86_64
+# define RWSEM_ACTIVE_MASK 0xffffffffL
+#else
+# define RWSEM_ACTIVE_MASK 0x0000ffffL
+#endif
+
+#define RWSEM_UNLOCKED_VALUE 0x00000000L
+#define RWSEM_ACTIVE_BIAS 0x00000001L
+#define RWSEM_WAITING_BIAS (-RWSEM_ACTIVE_MASK-1)
+#define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
+#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
+
+/*
+ * lock for reading
+ */
+#define ____down_read(sem, slow_path) \
+({ \
+ struct rw_semaphore* ret; \
+ asm volatile("# beginning down_read\n\t" \
+ LOCK_PREFIX _ASM_INC "(%[sem])\n\t" \
+ /* adds 0x00000001 */ \
+ " jns 1f\n" \
+ " call " slow_path "\n" \
+ "1:\n\t" \
+ "# ending down_read\n\t" \
+ : "+m" (sem->count), "=a" (ret), \
+ ASM_CALL_CONSTRAINT \
+ : [sem] "a" (sem) \
+ : "memory", "cc"); \
+ ret; \
+})
+
+static inline void __down_read(struct rw_semaphore *sem)
+{
+ ____down_read(sem, "call_rwsem_down_read_failed");
+}
+
+static inline int __down_read_killable(struct rw_semaphore *sem)
+{
+ if (IS_ERR(____down_read(sem, "call_rwsem_down_read_failed_killable")))
+ return -EINTR;
+ return 0;
+}
+
+/*
+ * trylock for reading -- returns 1 if successful, 0 if contention
+ */
+static inline bool __down_read_trylock(struct rw_semaphore *sem)
+{
+ long result, tmp;
+ asm volatile("# beginning __down_read_trylock\n\t"
+ " mov %[count],%[result]\n\t"
+ "1:\n\t"
+ " mov %[result],%[tmp]\n\t"
+ " add %[inc],%[tmp]\n\t"
+ " jle 2f\n\t"
+ LOCK_PREFIX " cmpxchg %[tmp],%[count]\n\t"
+ " jnz 1b\n\t"
+ "2:\n\t"
+ "# ending __down_read_trylock\n\t"
+ : [count] "+m" (sem->count), [result] "=&a" (result),
+ [tmp] "=&r" (tmp)
+ : [inc] "i" (RWSEM_ACTIVE_READ_BIAS)
+ : "memory", "cc");
+ return result >= 0;
+}
+
+/*
+ * lock for writing
+ */
+#define ____down_write(sem, slow_path) \
+({ \
+ long tmp; \
+ struct rw_semaphore* ret; \
+ \
+ asm volatile("# beginning down_write\n\t" \
+ LOCK_PREFIX " xadd %[tmp],(%[sem])\n\t" \
+ /* adds 0xffff0001, returns the old value */ \
+ " test " __ASM_SEL(%w1,%k1) "," __ASM_SEL(%w1,%k1) "\n\t" \
+ /* was the active mask 0 before? */\
+ " jz 1f\n" \
+ " call " slow_path "\n" \
+ "1:\n" \
+ "# ending down_write" \
+ : "+m" (sem->count), [tmp] "=d" (tmp), \
+ "=a" (ret), ASM_CALL_CONSTRAINT \
+ : [sem] "a" (sem), "[tmp]" (RWSEM_ACTIVE_WRITE_BIAS) \
+ : "memory", "cc"); \
+ ret; \
+})
+
+static inline void __down_write(struct rw_semaphore *sem)
+{
+ ____down_write(sem, "call_rwsem_down_write_failed");
+}
+
+static inline int __down_write_killable(struct rw_semaphore *sem)
+{
+ if (IS_ERR(____down_write(sem, "call_rwsem_down_write_failed_killable")))
+ return -EINTR;
+
+ return 0;
+}
+
+/*
+ * trylock for writing -- returns 1 if successful, 0 if contention
+ */
+static inline bool __down_write_trylock(struct rw_semaphore *sem)
+{
+ bool result;
+ long tmp0, tmp1;
+ asm volatile("# beginning __down_write_trylock\n\t"
+ " mov %[count],%[tmp0]\n\t"
+ "1:\n\t"
+ " test " __ASM_SEL(%w1,%k1) "," __ASM_SEL(%w1,%k1) "\n\t"
+ /* was the active mask 0 before? */
+ " jnz 2f\n\t"
+ " mov %[tmp0],%[tmp1]\n\t"
+ " add %[inc],%[tmp1]\n\t"
+ LOCK_PREFIX " cmpxchg %[tmp1],%[count]\n\t"
+ " jnz 1b\n\t"
+ "2:\n\t"
+ CC_SET(e)
+ "# ending __down_write_trylock\n\t"
+ : [count] "+m" (sem->count), [tmp0] "=&a" (tmp0),
+ [tmp1] "=&r" (tmp1), CC_OUT(e) (result)
+ : [inc] "er" (RWSEM_ACTIVE_WRITE_BIAS)
+ : "memory");
+ return result;
+}
+
+/*
+ * unlock after reading
+ */
+static inline void __up_read(struct rw_semaphore *sem)
+{
+ long tmp;
+ asm volatile("# beginning __up_read\n\t"
+ LOCK_PREFIX " xadd %[tmp],(%[sem])\n\t"
+ /* subtracts 1, returns the old value */
+ " jns 1f\n\t"
+ " call call_rwsem_wake\n" /* expects old value in %edx */
+ "1:\n"
+ "# ending __up_read\n"
+ : "+m" (sem->count), [tmp] "=d" (tmp)
+ : [sem] "a" (sem), "[tmp]" (-RWSEM_ACTIVE_READ_BIAS)
+ : "memory", "cc");
+}
+
+/*
+ * unlock after writing
+ */
+static inline void __up_write(struct rw_semaphore *sem)
+{
+ long tmp;
+ asm volatile("# beginning __up_write\n\t"
+ LOCK_PREFIX " xadd %[tmp],(%[sem])\n\t"
+ /* subtracts 0xffff0001, returns the old value */
+ " jns 1f\n\t"
+ " call call_rwsem_wake\n" /* expects old value in %edx */
+ "1:\n\t"
+ "# ending __up_write\n"
+ : "+m" (sem->count), [tmp] "=d" (tmp)
+ : [sem] "a" (sem), "[tmp]" (-RWSEM_ACTIVE_WRITE_BIAS)
+ : "memory", "cc");
+}
+
+/*
+ * downgrade write lock to read lock
+ */
+static inline void __downgrade_write(struct rw_semaphore *sem)
+{
+ asm volatile("# beginning __downgrade_write\n\t"
+ LOCK_PREFIX _ASM_ADD "%[inc],(%[sem])\n\t"
+ /*
+ * transitions 0xZZZZ0001 -> 0xYYYY0001 (i386)
+ * 0xZZZZZZZZ00000001 -> 0xYYYYYYYY00000001 (x86_64)
+ */
+ " jns 1f\n\t"
+ " call call_rwsem_downgrade_wake\n"
+ "1:\n\t"
+ "# ending __downgrade_write\n"
+ : "+m" (sem->count)
+ : [sem] "a" (sem), [inc] "er" (-RWSEM_WAITING_BIAS)
+ : "memory", "cc");
+}
+
+#endif /* __KERNEL__ */
+#endif /* _ASM_X86_RWSEM_H */
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