docs: RCU: Convert rcuref.txt to ReST
- Add a SPDX header; - Adjust document title; - Some whitespace fixes and new line breaks; - Mark literal blocks as such; - Add it to RCU/index.rst. Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Mauro Carvalho Chehab
Paul E. McKenney
parent
43cb5451df
commit
90c73cb2c6
|
|
@ -18,6 +18,7 @@ RCU concepts
|
|||
whatisRCU
|
||||
rcu
|
||||
rculist_nulls
|
||||
rcuref
|
||||
torture
|
||||
listRCU
|
||||
NMI-RCU
|
||||
|
|
|
|||
|
|
@ -1,4 +1,8 @@
|
|||
Reference-count design for elements of lists/arrays protected by RCU.
|
||||
.. SPDX-License-Identifier: GPL-2.0
|
||||
|
||||
====================================================================
|
||||
Reference-count design for elements of lists/arrays protected by RCU
|
||||
====================================================================
|
||||
|
||||
|
||||
Please note that the percpu-ref feature is likely your first
|
||||
|
|
@ -12,10 +16,11 @@ please read on.
|
|||
Reference counting on elements of lists which are protected by traditional
|
||||
reader/writer spinlocks or semaphores are straightforward:
|
||||
|
||||
CODE LISTING A:
|
||||
1. 2.
|
||||
add() search_and_reference()
|
||||
{ {
|
||||
CODE LISTING A::
|
||||
|
||||
1. 2.
|
||||
add() search_and_reference()
|
||||
{ {
|
||||
alloc_object read_lock(&list_lock);
|
||||
... search_for_element
|
||||
atomic_set(&el->rc, 1); atomic_inc(&el->rc);
|
||||
|
|
@ -23,16 +28,16 @@ add() search_and_reference()
|
|||
add_element read_unlock(&list_lock);
|
||||
... ...
|
||||
write_unlock(&list_lock); }
|
||||
}
|
||||
}
|
||||
|
||||
3. 4.
|
||||
release_referenced() delete()
|
||||
{ {
|
||||
3. 4.
|
||||
release_referenced() delete()
|
||||
{ {
|
||||
... write_lock(&list_lock);
|
||||
if(atomic_dec_and_test(&el->rc)) ...
|
||||
kfree(el);
|
||||
... remove_element
|
||||
} write_unlock(&list_lock);
|
||||
} write_unlock(&list_lock);
|
||||
...
|
||||
if (atomic_dec_and_test(&el->rc))
|
||||
kfree(el);
|
||||
|
|
@ -46,10 +51,11 @@ 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:
|
||||
|
||||
CODE LISTING B:
|
||||
1. 2.
|
||||
add() search_and_reference()
|
||||
{ {
|
||||
CODE LISTING B::
|
||||
|
||||
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)) {
|
||||
|
|
@ -58,15 +64,15 @@ add() search_and_reference()
|
|||
add_element }
|
||||
... ...
|
||||
spin_unlock(&list_lock); rcu_read_unlock();
|
||||
} }
|
||||
3. 4.
|
||||
release_referenced() delete()
|
||||
{ {
|
||||
} }
|
||||
3. 4.
|
||||
release_referenced() delete()
|
||||
{ {
|
||||
... spin_lock(&list_lock);
|
||||
if (atomic_dec_and_test(&el->rc)) ...
|
||||
call_rcu(&el->head, el_free); remove_element
|
||||
... spin_unlock(&list_lock);
|
||||
} ...
|
||||
} ...
|
||||
if (atomic_dec_and_test(&el->rc))
|
||||
call_rcu(&el->head, el_free);
|
||||
...
|
||||
|
|
@ -82,10 +88,11 @@ search_and_reference() code path. In such cases, the
|
|||
atomic_dec_and_test() may be moved from delete() to el_free()
|
||||
as follows:
|
||||
|
||||
CODE LISTING C:
|
||||
1. 2.
|
||||
add() search_and_reference()
|
||||
{ {
|
||||
CODE LISTING C::
|
||||
|
||||
1. 2.
|
||||
add() search_and_reference()
|
||||
{ {
|
||||
alloc_object rcu_read_lock();
|
||||
... search_for_element
|
||||
atomic_set(&el->rc, 1); atomic_inc(&el->rc);
|
||||
|
|
@ -94,20 +101,20 @@ add() search_and_reference()
|
|||
add_element rcu_read_unlock();
|
||||
... }
|
||||
spin_unlock(&list_lock); 4.
|
||||
} delete()
|
||||
3. {
|
||||
release_referenced() spin_lock(&list_lock);
|
||||
{ ...
|
||||
} delete()
|
||||
3. {
|
||||
release_referenced() spin_lock(&list_lock);
|
||||
{ ...
|
||||
... remove_element
|
||||
if (atomic_dec_and_test(&el->rc)) spin_unlock(&list_lock);
|
||||
kfree(el); ...
|
||||
... call_rcu(&el->head, el_free);
|
||||
} ...
|
||||
5. }
|
||||
void el_free(struct rcu_head *rhp)
|
||||
{
|
||||
} ...
|
||||
5. }
|
||||
void el_free(struct rcu_head *rhp)
|
||||
{
|
||||
release_referenced();
|
||||
}
|
||||
}
|
||||
|
||||
The key point is that the initial reference added by add() is not removed
|
||||
until after a grace period has elapsed following removal. This means that
|
||||
|
|
@ -130,11 +137,11 @@ the eventual invocation of kfree(), which is usually not a problem on
|
|||
modern computer systems, even the small ones.
|
||||
|
||||
In cases where delete() can sleep, synchronize_rcu() can be called from
|
||||
delete(), so that el_free() can be subsumed into delete as follows:
|
||||
delete(), so that el_free() can be subsumed into delete as follows::
|
||||
|
||||
4.
|
||||
delete()
|
||||
{
|
||||
4.
|
||||
delete()
|
||||
{
|
||||
spin_lock(&list_lock);
|
||||
...
|
||||
remove_element
|
||||
|
|
@ -144,7 +151,7 @@ delete()
|
|||
if (atomic_dec_and_test(&el->rc))
|
||||
kfree(el);
|
||||
...
|
||||
}
|
||||
}
|
||||
|
||||
As additional examples in the kernel, the pattern in listing C is used by
|
||||
reference counting of struct pid, while the pattern in listing B is used by
|
||||
Loading…
Reference in New Issue