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Commit 4b20db3de8dab005b07c74161cb041db8c5ff3a7

Authored by Thomas Hellstrom
Committed by Dave Airlie
1 parent d714455619
Exists in smarc-l5.0.0_1.0.0-ga and in 5 other branches imx_3.10.17_1.0.1_ga, imx_3.10.53_1.1.0_ga, imx_3.14.28_1.0.0_ga, smarc-imx_3.10.53_1.1.0_ga, smarc-imx_3.14.28_1.0.0_ga

kref: Implement kref_get_unless_zero v3 

This function is intended to simplify locking around refcounting for
objects that can be looked up from a lookup structure, and which are
removed from that lookup structure in the object destructor.
Operations on such objects require at least a read lock around
lookup + kref_get, and a write lock around kref_put + remove from lookup
structure. Furthermore, RCU implementations become extremely tricky.
With a lookup followed by a kref_get_unless_zero *with return value check*
locking in the kref_put path can be deferred to the actual removal from
the lookup structure and RCU lookups become trivial.

v2: Formatting fixes.
v3: Invert the return value.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

Showing 1 changed file with 21 additions and 0 deletions Side-by-side Diff

include/linux/kref.h
Diff comments   View file @ 4b20db3
... ... @@ -111,5 +111,26 @@
111 111 }
112 112 return 0;
113 113 }
  114 +
  115 +/**
  116 + * kref_get_unless_zero - Increment refcount for object unless it is zero.
  117 + * @kref: object.
  118 + *
  119 + * Return non-zero if the increment succeeded. Otherwise return 0.
  120 + *
  121 + * This function is intended to simplify locking around refcounting for
  122 + * objects that can be looked up from a lookup structure, and which are
  123 + * removed from that lookup structure in the object destructor.
  124 + * Operations on such objects require at least a read lock around
  125 + * lookup + kref_get, and a write lock around kref_put + remove from lookup
  126 + * structure. Furthermore, RCU implementations become extremely tricky.
  127 + * With a lookup followed by a kref_get_unless_zero *with return value check*
  128 + * locking in the kref_put path can be deferred to the actual removal from
  129 + * the lookup structure and RCU lookups become trivial.
  130 + */
  131 +static inline int __must_check kref_get_unless_zero(struct kref *kref)
  132 +{
  133 + return atomic_add_unless(&kref->refcount, 1, 0);
  134 +}
114 135 #endif /* _KREF_H_ */