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BUG/MEDIUM: threads: fix double-word CAS on non-optimized 32-bit platforms

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On armv7 haproxy doesn't work because of the fixes on the double-word
CAS. There are two issues. The first one is that the last argument in
case of dwcas is a pointer to the set of value and not a value ; the
second is that it's not enough to cast the data as (void*) since it will
be a single word. Let's fix this by using the pointers as an array of
long. This was tested on i386, armv7, x86_64 and aarch64 and it is now
fine. An alternate approach using a struct was attempted as well but it
used to produce less optimal code.

This fix must be backported to 1.9. This fixes github issue #105.

Cc: Olivier Houchard <ohouchard@haproxy.com>
This commit is contained in:
Willy Tarreau 2019-05-27 17:37:20 +02:00
parent bff005ae58
commit c3b5958255
2 changed files with 17 additions and 2 deletions
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17
include/common/hathreads.h
View File

@ -77,7 +77,19 @@ extern THREAD_LOCAL struct thread_info *ti; /* thread_info for the current threa
#define __decl_aligned_rwlock(lock)
#define HA_ATOMIC_CAS(val, old, new) ({((*val) == (*old)) ? (*(val) = (new) , 1) : (*(old) = *(val), 0);})
#define HA_ATOMIC_DWCAS(val, o, n) ({((*val) == (*o)) ? (*(val) = (n) , 1) : (*(o) = *(val), 0);})
/* warning, n is a pointer to the double value for dwcas */
#define HA_ATOMIC_DWCAS(val, o, n) \
({ \
long *_v = (long*)(val); \
long *_o = (long*)(o); \
long *_n = (long*)(n); \
long _v0 = _v[0], _v1 = _v[1]; \
(_v0 == _o[0] && _v1 == _o[1]) ? \
(_v[0] = _n[0], _v[1] = _n[1], 1) : \
(_o[0] = _v0, _o[1] = _v1, 0); \
})
#define HA_ATOMIC_ADD(val, i) ({*(val) += (i);})
#define HA_ATOMIC_SUB(val, i) ({*(val) -= (i);})
#define HA_ATOMIC_XADD(val, i) \
@ -293,6 +305,7 @@ static inline unsigned long thread_isolated()
__ret_cas; \
})
/* warning, n is a pointer to the double value for dwcas */
#define HA_ATOMIC_DWCAS(val, o, n) __ha_cas_dw(val, o, n)
#define HA_ATOMIC_XCHG(val, new) \
@ -337,6 +350,7 @@ static inline unsigned long thread_isolated()
#else
/* gcc >= 4.7 */
#define HA_ATOMIC_CAS(val, old, new) __atomic_compare_exchange_n(val, old, new, 0, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST)
/* warning, n is a pointer to the double value for dwcas */
#define HA_ATOMIC_DWCAS(val, o, n) __ha_cas_dw(val, o, n)
#define HA_ATOMIC_ADD(val, i) __atomic_add_fetch(val, i, __ATOMIC_SEQ_CST)
#define HA_ATOMIC_XADD(val, i) __atomic_fetch_add(val, i, __ATOMIC_SEQ_CST)
@ -366,6 +380,7 @@ static inline unsigned long thread_isolated()
* ie updating a counter. Otherwise a barrier is required.
*/
#define _HA_ATOMIC_CAS(val, old, new) __atomic_compare_exchange_n(val, old, new, 0, __ATOMIC_RELAXED, __ATOMIC_RELAXED)
/* warning, n is a pointer to the double value for dwcas */
#define _HA_ATOMIC_DWCAS(val, o, n) __ha_cas_dw(val, o, n)
#define _HA_ATOMIC_ADD(val, i) __atomic_add_fetch(val, i, __ATOMIC_RELAXED)
#define _HA_ATOMIC_XADD(val, i) __atomic_fetch_add(val, i, __ATOMIC_RELAXED)

2
src/fd.c
View File

@ -272,7 +272,7 @@ lock_self:
#ifdef HA_CAS_IS_8B
unlikely(!_HA_ATOMIC_CAS(((void **)(void *)&_GET_NEXT(fd, off)), ((void **)(void *)&cur_list), (*(void **)(void *)&next_list))))
#else
unlikely(!_HA_ATOMIC_DWCAS(((void **)(void *)&_GET_NEXT(fd, off)), ((void **)(void *)&cur_list), (*(void **)(void *)&next_list))))
unlikely(!_HA_ATOMIC_DWCAS(((void *)&_GET_NEXT(fd, off)), ((void *)&cur_list), ((void *)&next_list))))
#endif
;
next = cur_list.next;