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Re: [Qemu-devel] [PATCH v2 1/5] rcu: Add automatically released rcu_read
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH v2 1/5] rcu: Add automatically released rcu_read_lock variant |
Date: |
Thu, 12 Sep 2019 18:45:24 +0100 |
User-agent: |
Mutt/1.12.1 (2019-06-15) |
* Paolo Bonzini (address@hidden) wrote:
> On 11/09/19 21:06, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <address@hidden>
> >
> > RCU_READ_LOCK_AUTO takes the rcu_read_lock and then uses glib's
> > g_auto infrastructure (and thus whatever the compiler's hooks are) to
> > release it on all exits of the block.
> >
> > Signed-off-by: Dr. David Alan Gilbert <address@hidden>
> > ---
> > include/qemu/rcu.h | 18 ++++++++++++++++++
> > 1 file changed, 18 insertions(+)
> >
> > diff --git a/include/qemu/rcu.h b/include/qemu/rcu.h
> > index 22876d1428..8768a7b60a 100644
> > --- a/include/qemu/rcu.h
> > +++ b/include/qemu/rcu.h
> > @@ -154,6 +154,24 @@ extern void call_rcu1(struct rcu_head *head, RCUCBFunc
> > *func);
> > }), \
> > (RCUCBFunc *)g_free);
> >
> > +typedef void RCUReadAuto;
> > +static inline RCUReadAuto *rcu_read_auto_lock(void)
> > +{
> > + rcu_read_lock();
> > + /* Anything non-NULL causes the cleanup function to be called */
> > + return (void *)0x1;
>
> Doesn't this cause a warning (should be "(void *)(uintptr_t)1" instead)?
Apparently not, but I'll change it anyway.
> > +}
> > +
> > +static inline void rcu_read_auto_unlock(RCUReadAuto *r)
> > +{
> > + rcu_read_unlock();
> > +}
> > +
> > +G_DEFINE_AUTOPTR_CLEANUP_FUNC(RCUReadAuto, rcu_read_auto_unlock)
> > +
> > +#define RCU_READ_LOCK_AUTO \
> > + g_autoptr(RCUReadAuto) _rcu_read_auto = rcu_read_auto_lock()
> > +
> > #ifdef __cplusplus
> > }
> > #endif
> >
>
> Is it possible to make this a scope, like
>
> WITH_RCU_READ_LOCK() {
> }
>
> ? Perhaps something like
>
> #define WITH_RCU_READ_LOCK() \
> WITH_RCU_READ_LOCK_(_rcu_read_auto##__COUNTER__)
>
> #define WITH_RCU_READ_LOCK_(var) \
> for (g_autoptr(RCUReadAuto) var = rcu_read_auto_lock();
> (var); rcu_read_auto_unlock(), (var) = NULL)
>
> where the dummy variable doubles as an execute-once guard and the gauto
> cleanup is still used in case of a "break". I'm not sure if the above
> raises a warning because of the variable declaration inside the for
> loop, though.
Yes, that works - I'm not seeing any warnings.
Do you think it's best to use the block version for all cases
or to use the non-block version by taste?
The block version is quite nice, but that turns most of the patches
into 'indent everything'.
Dave
> Thanks,
>
> Paolo
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
[Qemu-devel] [PATCH v2 2/5] migration: Use automatic rcu_read unlock in ram.c, Dr. David Alan Gilbert (git), 2019/09/11
[Qemu-devel] [PATCH v2 3/5] migration: Use automatic rcu_read unlock in rdma.c, Dr. David Alan Gilbert (git), 2019/09/11
[Qemu-devel] [PATCH v2 5/5] migration: Missing rcu_read_unlock, Dr. David Alan Gilbert (git), 2019/09/11