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Use atomic_interrupt_fence() instead of bare __compiler_membar()

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for the which which definitely use membar to sync with interrupt handlers.

libc and rtld uses of __compiler_membar() seems to want compiler barriers
proper.

The barrier in sched_unpin_lite() after td_pinned decrement seems to be not
needed and removed, instead of convertion.

Reviewed by:	markj
MFC after:	1 week
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D28956
This commit is contained in:
Konstantin Belousov 2021-02-27 01:54:17 +02:00
parent 1d9ba697f9
commit b5449c92b4
5 changed files with 24 additions and 27 deletions
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32
sys/kern/kern_rmlock.c
View File

@ -366,7 +366,7 @@ _rm_rlock_hard(struct rmlock *rm, struct rm_priotracker *tracker, int trylock)
* Check to see if the IPI granted us the lock after all. The load of
* rmp_flags must happen after the tracker is removed from the list.
*/
__compiler_membar();
atomic_interrupt_fence();
if (tracker->rmp_flags) {
/* Just add back tracker - we hold the lock. */
rm_tracker_add(pc, tracker);
@ -448,7 +448,7 @@ _rm_rlock(struct rmlock *rm, struct rm_priotracker *tracker, int trylock)
td->td_critnest++; /* critical_enter(); */
__compiler_membar();
atomic_interrupt_fence();
pc = cpuid_to_pcpu[td->td_oncpu]; /* pcpu_find(td->td_oncpu); */
@ -456,7 +456,7 @@ _rm_rlock(struct rmlock *rm, struct rm_priotracker *tracker, int trylock)
sched_pin();
__compiler_membar();
atomic_interrupt_fence();
td->td_critnest--;
@ -873,17 +873,15 @@ db_show_rm(const struct lock_object *lock)
* Concurrent writers take turns taking the lock while going off cpu. If this is
* of concern for your usecase, this is not the right primitive.
*
* Neither rms_rlock nor rms_runlock use fences. Instead compiler barriers are
* inserted to prevert reordering of generated code. Execution ordering is
* provided with the use of an IPI handler.
* Neither rms_rlock nor rms_runlock use thread fences. Instead interrupt
* fences are inserted to ensure ordering with the code executed in the IPI
* handler.
*
* No attempt is made to track which CPUs read locked at least once,
* consequently write locking sends IPIs to all of them. This will become a
* problem at some point. The easiest way to lessen it is to provide a bitmap.
*/
#define rms_int_membar() __compiler_membar()
#define RMS_NOOWNER ((void *)0x1)
#define RMS_TRANSIENT ((void *)0x2)
#define RMS_FLAGMASK 0xf
@ -1030,14 +1028,14 @@ rms_rlock(struct rmslock *rms)
critical_enter();
pcpu = rms_int_pcpu(rms);
rms_int_influx_enter(rms, pcpu);
rms_int_membar();
atomic_interrupt_fence();
if (__predict_false(rms->writers > 0)) {
rms_rlock_fallback(rms);
return;
}
rms_int_membar();
atomic_interrupt_fence();
rms_int_readers_inc(rms, pcpu);
rms_int_membar();
atomic_interrupt_fence();
rms_int_influx_exit(rms, pcpu);
critical_exit();
}
@ -1052,15 +1050,15 @@ rms_try_rlock(struct rmslock *rms)
critical_enter();
pcpu = rms_int_pcpu(rms);
rms_int_influx_enter(rms, pcpu);
rms_int_membar();
atomic_interrupt_fence();
if (__predict_false(rms->writers > 0)) {
rms_int_influx_exit(rms, pcpu);
critical_exit();
return (0);
}
rms_int_membar();
atomic_interrupt_fence();
rms_int_readers_inc(rms, pcpu);
rms_int_membar();
atomic_interrupt_fence();
rms_int_influx_exit(rms, pcpu);
critical_exit();
return (1);
@ -1092,14 +1090,14 @@ rms_runlock(struct rmslock *rms)
critical_enter();
pcpu = rms_int_pcpu(rms);
rms_int_influx_enter(rms, pcpu);
rms_int_membar();
atomic_interrupt_fence();
if (__predict_false(rms->writers > 0)) {
rms_runlock_fallback(rms);
return;
}
rms_int_membar();
atomic_interrupt_fence();
rms_int_readers_dec(rms, pcpu);
rms_int_membar();
atomic_interrupt_fence();
rms_int_influx_exit(rms, pcpu);
critical_exit();
}

5
sys/sys/kpilite.h
View File

@ -38,7 +38,7 @@ sched_pin_lite(struct thread_lite *td)
KASSERT((struct thread *)td == curthread, ("sched_pin called on non curthread"));
td->td_pinned++;
__compiler_membar();
atomic_interrupt_fence();
}
static __inline void
@ -47,9 +47,8 @@ sched_unpin_lite(struct thread_lite *td)
KASSERT((struct thread *)td == curthread, ("sched_unpin called on non curthread"));
KASSERT(td->td_pinned > 0, ("sched_unpin called on non pinned thread"));
__compiler_membar();
atomic_interrupt_fence();
td->td_pinned--;
__compiler_membar();
}
#endif
#endif

4
sys/sys/mount.h
View File

@ -1091,7 +1091,7 @@ void resume_all_fs(void);
_mpcpu = vfs_mount_pcpu(mp); \
MPASS(mpcpu->mntp_thread_in_ops == 0); \
_mpcpu->mntp_thread_in_ops = 1; \
__compiler_membar(); \
atomic_interrupt_fence(); \
if (__predict_false(mp->mnt_vfs_ops > 0)) { \
vfs_op_thread_exit_crit(mp, _mpcpu); \
_retval_crit = false; \
@ -1111,7 +1111,7 @@ void resume_all_fs(void);
#define vfs_op_thread_exit_crit(mp, _mpcpu) do { \
MPASS(_mpcpu == vfs_mount_pcpu(mp)); \
MPASS(_mpcpu->mntp_thread_in_ops == 1); \
__compiler_membar(); \
atomic_interrupt_fence(); \
_mpcpu->mntp_thread_in_ops = 0; \
} while (0)

4
sys/sys/sched.h
View File

@ -173,13 +173,13 @@ static __inline void
sched_pin(void)
{
curthread->td_pinned++;
__compiler_membar();
atomic_interrupt_fence();
}
static __inline void
sched_unpin(void)
{
__compiler_membar();
atomic_interrupt_fence();
curthread->td_pinned--;
}

6
sys/sys/systm.h
View File

@ -284,7 +284,7 @@ critical_enter(void)
td = (struct thread_lite *)curthread;
td->td_critnest++;
__compiler_membar();
atomic_interrupt_fence();
}
static __inline void
@ -295,9 +295,9 @@ critical_exit(void)
td = (struct thread_lite *)curthread;
KASSERT(td->td_critnest != 0,
("critical_exit: td_critnest == 0"));
__compiler_membar();
atomic_interrupt_fence();
td->td_critnest--;
__compiler_membar();
atomic_interrupt_fence();
if (__predict_false(td->td_owepreempt))
critical_exit_preempt();