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authorChunwei Chen <[email protected]>2016-05-25 16:35:42 -0700
committerBrian Behlendorf <[email protected]>2016-05-31 11:44:15 -0700
commitf58040c0fc8bc6490fcc75db7fc3e709dfc3c656 (patch)
tree03aaebb8e0e152ade6edb7a9ae14f4b430314797 /include/sys/rwlock.h
parentc60a51b640bab61c54f370752750841675730899 (diff)
Implement a proper rw_tryupgrade
Current rw_tryupgrade does rw_exit and then rw_tryenter(RW_RWITER), and then does rw_enter(RW_READER) if it fails. This violate the assumption that rw_tryupgrade should be atomic and could cause extra contention or even lock inversion. This patch we implement a proper rw_tryupgrade. For rwsem-spinlock, we take the spinlock to check rwsem->count and rwsem->wait_list. For normal rwsem, we use cmpxchg on rwsem->count to change the value from single reader to single writer. Signed-off-by: Chunwei Chen <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Signed-off-by: Tim Chase <[email protected]> Closes zfsonlinux/zfs#4692 Closes #554
Diffstat (limited to 'include/sys/rwlock.h')
-rw-r--r--include/sys/rwlock.h11
1 files changed, 4 insertions, 7 deletions
diff --git a/include/sys/rwlock.h b/include/sys/rwlock.h
index 14d097b01..facebe3ba 100644
--- a/include/sys/rwlock.h
+++ b/include/sys/rwlock.h
@@ -223,13 +223,10 @@ RW_LOCK_HELD(krwlock_t *rwp)
if (RW_WRITE_HELD(rwp)) { \
_rc_ = 1; \
} else { \
- rw_exit(rwp); \
- if (rw_tryenter(rwp, RW_WRITER)) { \
- _rc_ = 1; \
- } else { \
- rw_enter(rwp, RW_READER); \
- _rc_ = 0; \
- } \
+ spl_rw_lockdep_off_maybe(rwp); \
+ if ((_rc_ = rwsem_tryupgrade(SEM(rwp)))) \
+ spl_rw_set_owner(rwp); \
+ spl_rw_lockdep_on_maybe(rwp); \
} \
_rc_; \
})