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Message-ID: <aL_4gCJibYMW0J98@gondor.apana.org.au>
Date: Tue, 9 Sep 2025 17:50:56 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
Steven Rostedt <rostedt@...dmis.org>,
Menglong Dong <dongml2@...natelecom.cn>,
mathieu.desnoyers@...icios.com, linux-kernel@...r.kernel.org,
linux-trace-kernel@...r.kernel.org,
kernel test robot <oliver.sang@...el.com>, tgraf@...g.ch,
linux-crypto@...r.kernel.org
Subject: [v2 PATCH] rhashtable: Use rcu_dereference_all and
rcu_dereference_all_check
On Mon, Sep 08, 2025 at 08:23:27AM -0700, Paul E. McKenney wrote:
>
> I am guessing that you want to send this up via the rhashtable path.
Yes I could push that along.
> * This is similar to rcu_dereference_check(), but allows protection
> * by all forms of vanilla RCU readers, including preemption disabled,
> * bh-disabled, and interrupt-disabled regions of code. Note that "vanilla
> * RCU" excludes SRCU and the various Tasks RCU flavors. Please note
> * that this macro should not be backported to any Linux-kernel version
> * preceding v5.0 due to changes in synchronize_rcu() semantics prior
> * to that version.
>
> The "should not" vs. "can not" accounts for the possibility of people
> using synchronize_rcu_mult(), but someone wanting to do that best know
> what they are doing. ;-)
Thanks! I've incorported that into the patch:
---8<---
Add rcu_dereference_all and rcu_dereference_all_check so that
library code such as rhashtable can be used with any RCU variant.
As it stands rcu_dereference is used within rashtable, which
creates false-positive warnings if the user calls it from another
RCU context, such as preempt_disable().
Use the rcu_dereference_all and rcu_dereference_all_check calls
in rhashtable to suppress these warnings.
Also replace the rcu_dereference_raw calls in the list iterators
with rcu_dereference_all to uncover buggy calls.
Reported-by: Menglong Dong <dongml2@...natelecom.cn>
Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
Reviewed-by: Paul E. McKenney <paulmck@...nel.org>
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 120536f4c6eb..448eb1f0cb48 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -713,6 +713,24 @@ do { \
(c) || rcu_read_lock_sched_held(), \
__rcu)
+/**
+ * rcu_dereference_all_check() - rcu_dereference_all with debug checking
+ * @p: The pointer to read, prior to dereferencing
+ * @c: The conditions under which the dereference will take place
+ *
+ * This is similar to rcu_dereference_check(), but allows protection
+ * by all forms of vanilla RCU readers, including preemption disabled,
+ * bh-disabled, and interrupt-disabled regions of code. Note that "vanilla
+ * RCU" excludes SRCU and the various Tasks RCU flavors. Please note
+ * that this macro should not be backported to any Linux-kernel version
+ * preceding v5.0 due to changes in synchronize_rcu() semantics prior
+ * to that version.
+ */
+#define rcu_dereference_all_check(p, c) \
+ __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
+ (c) || rcu_read_lock_any_held(), \
+ __rcu)
+
/*
* The tracing infrastructure traces RCU (we want that), but unfortunately
* some of the RCU checks causes tracing to lock up the system.
@@ -767,6 +785,14 @@ do { \
*/
#define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
+/**
+ * rcu_dereference_all() - fetch RCU-all-protected pointer for dereferencing
+ * @p: The pointer to read, prior to dereferencing
+ *
+ * Makes rcu_dereference_check() do the dirty work.
+ */
+#define rcu_dereference_all(p) rcu_dereference_all_check(p, 0)
+
/**
* rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism
* @p: The pointer to hand off
diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index e740157f3cd7..05a221ce79a6 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -272,13 +272,13 @@ struct rhash_lock_head __rcu **rht_bucket_nested_insert(
rcu_dereference_protected(p, lockdep_rht_mutex_is_held(ht))
#define rht_dereference_rcu(p, ht) \
- rcu_dereference_check(p, lockdep_rht_mutex_is_held(ht))
+ rcu_dereference_all_check(p, lockdep_rht_mutex_is_held(ht))
#define rht_dereference_bucket(p, tbl, hash) \
rcu_dereference_protected(p, lockdep_rht_bucket_is_held(tbl, hash))
#define rht_dereference_bucket_rcu(p, tbl, hash) \
- rcu_dereference_check(p, lockdep_rht_bucket_is_held(tbl, hash))
+ rcu_dereference_all_check(p, lockdep_rht_bucket_is_held(tbl, hash))
#define rht_entry(tpos, pos, member) \
({ tpos = container_of(pos, typeof(*tpos), member); 1; })
@@ -373,7 +373,7 @@ static inline struct rhash_head *__rht_ptr(
static inline struct rhash_head *rht_ptr_rcu(
struct rhash_lock_head __rcu *const *bkt)
{
- return __rht_ptr(rcu_dereference(*bkt), bkt);
+ return __rht_ptr(rcu_dereference_all(*bkt), bkt);
}
static inline struct rhash_head *rht_ptr(
@@ -497,7 +497,7 @@ static inline void rht_assign_unlock(struct bucket_table *tbl,
for (({barrier(); }), \
pos = head; \
!rht_is_a_nulls(pos); \
- pos = rcu_dereference_raw(pos->next))
+ pos = rcu_dereference_all(pos->next))
/**
* rht_for_each_rcu - iterate over rcu hash chain
@@ -513,7 +513,7 @@ static inline void rht_assign_unlock(struct bucket_table *tbl,
for (({barrier(); }), \
pos = rht_ptr_rcu(rht_bucket(tbl, hash)); \
!rht_is_a_nulls(pos); \
- pos = rcu_dereference_raw(pos->next))
+ pos = rcu_dereference_all(pos->next))
/**
* rht_for_each_entry_rcu_from - iterated over rcu hash chain from given head
@@ -560,7 +560,7 @@ static inline void rht_assign_unlock(struct bucket_table *tbl,
* list returned by rhltable_lookup.
*/
#define rhl_for_each_rcu(pos, list) \
- for (pos = list; pos; pos = rcu_dereference_raw(pos->next))
+ for (pos = list; pos; pos = rcu_dereference_all(pos->next))
/**
* rhl_for_each_entry_rcu - iterate over rcu hash table list of given type
@@ -574,7 +574,7 @@ static inline void rht_assign_unlock(struct bucket_table *tbl,
*/
#define rhl_for_each_entry_rcu(tpos, pos, list, member) \
for (pos = list; pos && rht_entry(tpos, pos, member); \
- pos = rcu_dereference_raw(pos->next))
+ pos = rcu_dereference_all(pos->next))
static inline int rhashtable_compare(struct rhashtable_compare_arg *arg,
const void *obj)
--
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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