https://github.com/torvalds/linux
Revision 85746e429f8e5dc8c5c0beadc0f099cb1feab93e authored by Linus Torvalds on 07 July 2011, 20:16:21 UTC, committed by Linus Torvalds on 07 July 2011, 20:16:21 UTC
* git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-2.6: (31 commits) sctp: fix missing send up SCTP_SENDER_DRY_EVENT when subscribe it net: refine {udp|tcp|sctp}_mem limits vmxnet3: round down # of queues to power of two net: sh_eth: fix the parameter for the ETHER of SH7757 net: sh_eth: fix cannot work half-duplex mode net: vlan: enable soft features regardless of underlying device vmxnet3: fix starving rx ring whenoc_skb kb fails bridge: Always flood broadcast packets greth: greth_set_mac_add would corrupt the MAC address. net: bind() fix error return on wrong address family natsemi: silence dma-debug warnings net: 8139too: Initial necessary vlan_features to support vlan Fix call trace when interrupts are disabled while sleeping function kzalloc is called qlge:Version change to v1.00.00.29 qlge: Fix printk priority so chip fatal errors are always reported. qlge:Fix crash caused by mailbox execution on wedged chip. xfrm4: Don't call icmp_send on local error ipv4: Don't use ufo handling on later transformed packets xfrm: Remove family arg from xfrm_bundle_ok ipv6: Don't put artificial limit on routing table size. ...
Tip revision: 85746e429f8e5dc8c5c0beadc0f099cb1feab93e authored by Linus Torvalds on 07 July 2011, 20:16:21 UTC
Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-2.6
Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-2.6
Tip revision: 85746e4
rcuref.txt
Reference-count design for elements of lists/arrays protected by RCU.
Reference counting on elements of lists which are protected by traditional
reader/writer spinlocks or semaphores are straightforward:
1. 2.
add() search_and_reference()
{ {
alloc_object read_lock(&list_lock);
... search_for_element
atomic_set(&el->rc, 1); atomic_inc(&el->rc);
write_lock(&list_lock); ...
add_element read_unlock(&list_lock);
... ...
write_unlock(&list_lock); }
}
3. 4.
release_referenced() delete()
{ {
... write_lock(&list_lock);
atomic_dec(&el->rc, relfunc) ...
... delete_element
} write_unlock(&list_lock);
...
if (atomic_dec_and_test(&el->rc))
kfree(el);
...
}
If this list/array is made lock free using RCU as in changing the
write_lock() in add() and delete() to spin_lock() and changing read_lock()
in search_and_reference() to rcu_read_lock(), the atomic_inc() in
search_and_reference() could potentially hold reference to an element which
has already been deleted from the list/array. Use atomic_inc_not_zero()
in this scenario as follows:
1. 2.
add() search_and_reference()
{ {
alloc_object rcu_read_lock();
... search_for_element
atomic_set(&el->rc, 1); if (!atomic_inc_not_zero(&el->rc)) {
spin_lock(&list_lock); rcu_read_unlock();
return FAIL;
add_element }
... ...
spin_unlock(&list_lock); rcu_read_unlock();
} }
3. 4.
release_referenced() delete()
{ {
... spin_lock(&list_lock);
if (atomic_dec_and_test(&el->rc)) ...
call_rcu(&el->head, el_free); delete_element
... spin_unlock(&list_lock);
} ...
if (atomic_dec_and_test(&el->rc))
call_rcu(&el->head, el_free);
...
}
Sometimes, a reference to the element needs to be obtained in the
update (write) stream. In such cases, atomic_inc_not_zero() might be
overkill, since we hold the update-side spinlock. One might instead
use atomic_inc() in such cases.
Computing file changes ...