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doc/RCU/listRCU: refine example code for eliminating stale data 

This patch adjust the example code with following two purpose:

  * reduce the confusion on not releasing e->lock
  * emphasize e is valid and not stale with e->lock held

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
CC: Boqun Feng <boqun.feng@gmail.com>
CC: Alan Huang <mmpgouride@gmail.com>
Reviewed-by: Alan Huang <mmpgouride@gmail.com>
Link: https://lore.kernel.org/r/20250218005047.27258-1-richard.weiyang@gmail.com
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
This commit is contained in:
Wei Yang 2025-02-18 00:50:47 +00:00 committed by Joel Fernandes
parent 1708bf2cc4
commit 79ea7f43f8
1 changed files with 6 additions and 4 deletions
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10
Documentation/RCU/listRCU.rst
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@ -334,7 +334,7 @@ If the system-call audit module were to ever need to reject stale data, one way
to accomplish this would be to add a ``deleted`` flag and a ``lock`` spinlock to the to accomplish this would be to add a ``deleted`` flag and a ``lock`` spinlock to the
``audit_entry`` structure, and modify audit_filter_task() as follows:: ``audit_entry`` structure, and modify audit_filter_task() as follows::
static enum audit_state audit_filter_task(struct task_struct *tsk) static struct audit_entry *audit_filter_task(struct task_struct *tsk, char **key)
{ {
struct audit_entry *e; struct audit_entry *e;
enum audit_state state; enum audit_state state;
@ -346,16 +346,18 @@ to accomplish this would be to add a ``deleted`` flag and a ``lock`` spinlock to
if (e->deleted) { if (e->deleted) {
spin_unlock(&e->lock); spin_unlock(&e->lock);
rcu_read_unlock(); rcu_read_unlock();
return AUDIT_BUILD_CONTEXT; return NULL;
} }
rcu_read_unlock(); rcu_read_unlock();
if (state == AUDIT_STATE_RECORD) if (state == AUDIT_STATE_RECORD)
*key = kstrdup(e->rule.filterkey, GFP_ATOMIC); *key = kstrdup(e->rule.filterkey, GFP_ATOMIC);
return state; /* As long as e->lock is held, e is valid and
* its value is not stale */
return e;
} }
} }
rcu_read_unlock(); rcu_read_unlock();
return AUDIT_BUILD_CONTEXT; return NULL;
} }
The ``audit_del_rule()`` function would need to set the ``deleted`` flag under the The ``audit_del_rule()`` function would need to set the ``deleted`` flag under the