Hi Herbert, On Tue, Sep 09, 2025 at 05:50:56PM +0800, Herbert Xu wrote: > 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 <[email protected]> > Signed-off-by: Herbert Xu <[email protected]> > Reviewed-by: Paul E. McKenney <[email protected]>
We hit the same issue in sched_ext and with this applied lockep seems happy. FWIW: Tested-by: Andrea Righi <[email protected]> Thanks, -Andrea > > 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 <[email protected]> > Home Page: http://gondor.apana.org.au/~herbert/ > PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
