| Message ID | 20240325183907.7205bf36489a.Ic3ac66ff5d6a9bd8a610858060117e1364641a3f@changeid (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | d8e9d65e923a7a63e1c39a936dadf8e12b9ff40c |
| Headers | show |
| Series | [v2] rcu: mollify sparse with RCU guard | expand |
On Mon, Mar 25, 2024 at 06:39:08PM +0100, Johannes Berg wrote: > From: Johannes Berg <johannes.berg@intel.com> > > When using "guard(rcu)();" sparse will complain, because even > though it now understands the cleanup attribute, it doesn't > evaluate the calls from it at function exit, and thus doesn't > count the context correctly. > > Given that there's a conditional in the resulting code: > > static inline void class_rcu_destructor(class_rcu_t *_T) > { > if (_T->lock) { > rcu_read_unlock(); > } > } > > it seems that even trying to teach sparse to evalulate the > cleanup attribute function it'd still be difficult to really > make it understand the full context here. > > Suppress the sparse warning by just releasing the context in > the acquisition part of the function, after all we know it's > safe with the guard, that's the whole point of it. > > Signed-off-by: Johannes Berg <johannes.berg@intel.com> Reviewed-by: Boqun Feng <boqun.feng@gmail.com> Regards, Boqun > --- > v2: add a comment after discussion with Boqun > > --- > include/linux/rcupdate.h | 14 +++++++++++++- > 1 file changed, 13 insertions(+), 1 deletion(-) > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > index 0746b1b0b663..6a3c52b3c180 100644 > --- a/include/linux/rcupdate.h > +++ b/include/linux/rcupdate.h > @@ -1059,6 +1059,18 @@ rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f) > extern int rcu_expedited; > extern int rcu_normal; > > -DEFINE_LOCK_GUARD_0(rcu, rcu_read_lock(), rcu_read_unlock()) > +DEFINE_LOCK_GUARD_0(rcu, > + do { > + rcu_read_lock(); > + /* > + * sparse doesn't call the cleanup function, > + * so just release immediately and don't track > + * the context. We don't need to anyway, since > + * the whole point of the guard is to not need > + * the explicit unlock. > + */ > + __release(RCU); > + } while(0), > + rcu_read_unlock()) > > #endif /* __LINUX_RCUPDATE_H */ > -- > 2.44.0 >
On Mon, Mar 25, 2024 at 10:41:36AM -0700, Boqun Feng wrote: > On Mon, Mar 25, 2024 at 06:39:08PM +0100, Johannes Berg wrote: > > From: Johannes Berg <johannes.berg@intel.com> > > > > When using "guard(rcu)();" sparse will complain, because even > > though it now understands the cleanup attribute, it doesn't > > evaluate the calls from it at function exit, and thus doesn't > > count the context correctly. > > > > Given that there's a conditional in the resulting code: > > > > static inline void class_rcu_destructor(class_rcu_t *_T) > > { > > if (_T->lock) { > > rcu_read_unlock(); > > } > > } > > > > it seems that even trying to teach sparse to evalulate the > > cleanup attribute function it'd still be difficult to really > > make it understand the full context here. > > > > Suppress the sparse warning by just releasing the context in > > the acquisition part of the function, after all we know it's > > safe with the guard, that's the whole point of it. > > > > Signed-off-by: Johannes Berg <johannes.berg@intel.com> > > Reviewed-by: Boqun Feng <boqun.feng@gmail.com> Queued, thank you both! Thanx, Paul > Regards, > Boqun > > > --- > > v2: add a comment after discussion with Boqun > > > > --- > > include/linux/rcupdate.h | 14 +++++++++++++- > > 1 file changed, 13 insertions(+), 1 deletion(-) > > > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > > index 0746b1b0b663..6a3c52b3c180 100644 > > --- a/include/linux/rcupdate.h > > +++ b/include/linux/rcupdate.h > > @@ -1059,6 +1059,18 @@ rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f) > > extern int rcu_expedited; > > extern int rcu_normal; > > > > -DEFINE_LOCK_GUARD_0(rcu, rcu_read_lock(), rcu_read_unlock()) > > +DEFINE_LOCK_GUARD_0(rcu, > > + do { > > + rcu_read_lock(); > > + /* > > + * sparse doesn't call the cleanup function, > > + * so just release immediately and don't track > > + * the context. We don't need to anyway, since > > + * the whole point of the guard is to not need > > + * the explicit unlock. > > + */ > > + __release(RCU); > > + } while(0), > > + rcu_read_unlock()) > > > > #endif /* __LINUX_RCUPDATE_H */ > > -- > > 2.44.0 > >
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 0746b1b0b663..6a3c52b3c180 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -1059,6 +1059,18 @@ rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f) extern int rcu_expedited; extern int rcu_normal; -DEFINE_LOCK_GUARD_0(rcu, rcu_read_lock(), rcu_read_unlock()) +DEFINE_LOCK_GUARD_0(rcu, + do { + rcu_read_lock(); + /* + * sparse doesn't call the cleanup function, + * so just release immediately and don't track + * the context. We don't need to anyway, since + * the whole point of the guard is to not need + * the explicit unlock. + */ + __release(RCU); + } while(0), + rcu_read_unlock()) #endif /* __LINUX_RCUPDATE_H */