Release 4.15 arch/x86/include/asm/rwsem.h
/* 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");
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Linus Torvalds | 11 | 57.89% | 1 | 50.00% |
| Kirill Tkhai | 8 | 42.11% | 1 | 50.00% |
| Total | 19 | 100.00% | 2 | 100.00% |
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;
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Kirill Tkhai | 30 | 96.77% | 1 | 50.00% |
| Linus Torvalds | 1 | 3.23% | 1 | 50.00% |
| Total | 31 | 100.00% | 2 | 100.00% |
/*
* 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;
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Christoph Hellwig | 20 | 80.00% | 1 | 20.00% |
| Joe Perches | 2 | 8.00% | 1 | 20.00% |
| H. Peter Anvin | 1 | 4.00% | 1 | 20.00% |
| Miguel Bernal Marin | 1 | 4.00% | 1 | 20.00% |
| Thomas Gleixner | 1 | 4.00% | 1 | 20.00% |
| Total | 25 | 100.00% | 5 | 100.00% |
/*
* 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");
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Linus Torvalds | 10 | 52.63% | 1 | 33.33% |
| Michal Hocko | 9 | 47.37% | 2 | 66.67% |
| Total | 19 | 100.00% | 3 | 100.00% |
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;
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Michal Hocko | 30 | 96.77% | 1 | 50.00% |
| Linus Torvalds | 1 | 3.23% | 1 | 50.00% |
| Total | 31 | 100.00% | 2 | 100.00% |
/*
* 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;
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Christoph Hellwig | 14 | 50.00% | 1 | 25.00% |
| Michel Lespinasse | 6 | 21.43% | 1 | 25.00% |
| H. Peter Anvin | 6 | 21.43% | 1 | 25.00% |
| Miguel Bernal Marin | 2 | 7.14% | 1 | 25.00% |
| Total | 28 | 100.00% | 4 | 100.00% |
/*
* 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");
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Linus Torvalds | 15 | 68.18% | 2 | 33.33% |
| Joe Perches | 2 | 9.09% | 1 | 16.67% |
| Michel Lespinasse | 2 | 9.09% | 1 | 16.67% |
| Miguel Bernal Marin | 2 | 9.09% | 1 | 16.67% |
| Thomas Gleixner | 1 | 4.55% | 1 | 16.67% |
| Total | 22 | 100.00% | 6 | 100.00% |
/*
* 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");
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Linus Torvalds | 14 | 63.64% | 2 | 28.57% |
| Michel Lespinasse | 3 | 13.64% | 2 | 28.57% |
| Joe Perches | 2 | 9.09% | 1 | 14.29% |
| Miguel Bernal Marin | 2 | 9.09% | 1 | 14.29% |
| Thomas Gleixner | 1 | 4.55% | 1 | 14.29% |
| Total | 22 | 100.00% | 7 | 100.00% |
/*
* 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");
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| David Howells | 12 | 70.59% | 1 | 25.00% |
| Miguel Bernal Marin | 2 | 11.76% | 1 | 25.00% |
| Joe Perches | 2 | 11.76% | 1 | 25.00% |
| Avi Kivity | 1 | 5.88% | 1 | 25.00% |
| Total | 17 | 100.00% | 4 | 100.00% |
#endif /* __KERNEL__ */
#endif /* _ASM_X86_RWSEM_H */
Overall Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Linus Torvalds | 94 | 30.23% | 5 | 20.83% |
| Michal Hocko | 51 | 16.40% | 2 | 8.33% |
| Kirill Tkhai | 50 | 16.08% | 1 | 4.17% |
| Christoph Hellwig | 36 | 11.58% | 1 | 4.17% |
| H. Peter Anvin | 29 | 9.32% | 3 | 12.50% |
| David Howells | 13 | 4.18% | 1 | 4.17% |
| Michel Lespinasse | 11 | 3.54% | 3 | 12.50% |
| Miguel Bernal Marin | 11 | 3.54% | 1 | 4.17% |
| Joe Perches | 8 | 2.57% | 1 | 4.17% |
| Thomas Gleixner | 4 | 1.29% | 2 | 8.33% |
| Avi Kivity | 1 | 0.32% | 1 | 4.17% |
| Michael Hayes | 1 | 0.32% | 1 | 4.17% |
| Adam Buchbinder | 1 | 0.32% | 1 | 4.17% |
| Greg Kroah-Hartman | 1 | 0.32% | 1 | 4.17% |
| Total | 311 | 100.00% | 24 | 100.00% |
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