| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-Id: <20180731041425.GI24813@linux.vnet.ibm.com>
Date: Mon, 30 Jul 2018 21:14:25 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: NeilBrown <neilb@...e.com>
Cc: Herbert Xu <herbert@...dor.apana.org.au>,
Thomas Graf <tgraf@...g.ch>, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] rhashtable: don't hold lock on first table
throughout insertion.
On Tue, Jul 31, 2018 at 10:45:45AM +1000, NeilBrown wrote:
> On Fri, Jul 27 2018, Paul E. McKenney wrote:
>
> > On Thu, Jul 26, 2018 at 08:18:15PM -0700, Paul E. McKenney wrote:
> >> On Fri, Jul 27, 2018 at 11:04:37AM +1000, NeilBrown wrote:
> >> > On Wed, Jul 25 2018, Paul E. McKenney wrote:
> >> > >>
> >> > >> Looks good ... except ... naming is hard.
> >> > >>
> >> > >> is_after_call_rcu_init() asserts where in the lifecycle we are,
> >> > >> is_after_call_rcu() tests where in the lifecycle we are.
> >> > >>
> >> > >> The names are similar but the purpose is quite different.
> >> > >> Maybe s/is_after_call_rcu_init/call_rcu_init/ ??
> >> > >
> >> > > How about rcu_head_init() and rcu_head_after_call_rcu()?
> >>
> >> Very well, I will pull this change in on my next rebase.
> >
> > Like this?
>
> Hard to say - unwinding white-space damage in my head is too challenging
> when newlines have been deleted :-(
What??? Don't you like block-structured code?
All kidding aside, how about the following more conventionally formatted
version?
Thanx, Paul
------------------------------------------------------------------------
commit e3408141ed7d702995b2fdc94703af88aadd226b
Author: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Date: Tue Jul 24 15:28:09 2018 -0700
rcu: Provide functions for determining if call_rcu() has been invoked
This commit adds rcu_head_init() and rcu_head_after_call_rcu() functions
to help RCU users detect when another CPU has passed the specified
rcu_head structure and function to call_rcu(). The rcu_head_init()
should be invoked before making the structure visible to RCU readers,
and then the rcu_head_after_call_rcu() may be invoked from within
an RCU read-side critical section on an rcu_head structure that
was obtained during a traversal of the data structure in question.
The rcu_head_after_call_rcu() function will return true if the rcu_head
structure has already been passed (with the specified function) to
call_rcu(), otherwise it will return false.
If rcu_head_init() has not been invoked on the rcu_head structure
or if the rcu_head (AKA callback) has already been invoked, then
rcu_head_after_call_rcu() will do WARN_ON_ONCE().
Reported-by: NeilBrown <neilb@...e.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
[ paulmck: Apply neilb naming feedback. ]
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index e4f821165d0b..4db8bcacc51a 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -857,6 +857,46 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
#endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
+/* Has the specified rcu_head structure been handed to call_rcu()? */
+
+/*
+ * rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu()
+ * @rhp: The rcu_head structure to initialize.
+ *
+ * If you intend to invoke rcu_head_after_call_rcu() to test whether a
+ * given rcu_head structure has already been passed to call_rcu(), then
+ * you must also invoke this rcu_head_init() function on it just after
+ * allocating that structure. Calls to this function must not race with
+ * calls to call_rcu(), rcu_head_after_call_rcu(), or callback invocation.
+ */
+static inline void rcu_head_init(struct rcu_head *rhp)
+{
+ rhp->func = (rcu_callback_t)~0L;
+}
+
+/*
+ * rcu_head_after_call_rcu - Has this rcu_head been passed to call_rcu()?
+ * @rhp: The rcu_head structure to test.
+ * @func: The function passed to call_rcu() along with @rhp.
+ *
+ * Returns @true if the @rhp has been passed to call_rcu() with @func,
+ * and @false otherwise. Emits a warning in any other case, including
+ * the case where @rhp has already been invoked after a grace period.
+ * Calls to this function must not race with callback invocation. One way
+ * to avoid such races is to enclose the call to rcu_head_after_call_rcu()
+ * in an RCU read-side critical section that includes a read-side fetch
+ * of the pointer to the structure containing @rhp.
+ */
+static inline bool
+rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f)
+{
+ if (READ_ONCE(rhp->func) == f)
+ return true;
+ WARN_ON_ONCE(READ_ONCE(rhp->func) != (rcu_callback_t)~0L);
+ return false;
+}
+
+
/* Transitional pre-consolidation compatibility definitions. */
static inline void synchronize_rcu_bh(void)
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 5dec94509a7e..4c56c1d98fb3 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -224,6 +224,7 @@ void kfree(const void *);
*/
static inline bool __rcu_reclaim(const char *rn, struct rcu_head *head)
{
+ rcu_callback_t f;
unsigned long offset = (unsigned long)head->func;
rcu_lock_acquire(&rcu_callback_map);
@@ -234,7 +235,9 @@ static inline bool __rcu_reclaim(const char *rn, struct rcu_head *head)
return true;
} else {
RCU_TRACE(trace_rcu_invoke_callback(rn, head);)
- head->func(head);
+ f = head->func;
+ WRITE_ONCE(head->func, (rcu_callback_t)0L);
+ f(head);
rcu_lock_release(&rcu_callback_map);
return false;
}
Powered by blists - more mailing lists