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([2001:b07:6468:f312:c5d2:4bb2:a923:3a9a]) by smtp.gmail.com with ESMTPSA id u18sm2017487wmj.11.2019.09.13.05.01.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 13 Sep 2019 05:01:02 -0700 (PDT) To: "Dr. David Alan Gilbert (git)" , qemu-devel@nongnu.org, ehabkost@redhat.com, berrange@redhat.com, quintela@redhat.com References: <20190913102538.24167-1-dgilbert@redhat.com> <20190913102538.24167-2-dgilbert@redhat.com> From: Paolo Bonzini Openpgp: preference=signencrypt Message-ID: Date: Fri, 13 Sep 2019 14:01:03 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190913102538.24167-2-dgilbert@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH v3 1/5] rcu: Add automatically released rcu_read_lock variants X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 13/09/19 12:25, Dr. David Alan Gilbert (git) wrote: > From: "Dr. David Alan Gilbert" > > RCU_READ_LOCK_GUARD() 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. > > WITH_RCU_READ_LOCK_GUARD() is similar but is used as a wrapper for the > lock, i.e.: > > WITH_RCU_READ_LOCK_GUARD() { > stuff under lock > } > > Signed-off-by: Dr. David Alan Gilbert > --- > docs/devel/rcu.txt | 16 ++++++++++++++++ > include/qemu/rcu.h | 25 +++++++++++++++++++++++++ > 2 files changed, 41 insertions(+) > > diff --git a/docs/devel/rcu.txt b/docs/devel/rcu.txt > index c84e7f42b2..d83fed2f79 100644 > --- a/docs/devel/rcu.txt > +++ b/docs/devel/rcu.txt > @@ -187,6 +187,22 @@ The following APIs must be used before RCU is used in a thread: > Note that these APIs are relatively heavyweight, and should _not_ be > nested. > > +Convenience macros > +================== > + > +Two macros are provided that automatically release the read lock at the > +end of the scope. > + > + RCU_READ_LOCK_GUARD() > + > + Takes the lock and will release it at the end of the block it's > + used in. > + > + WITH_RCU_READ_LOCK_GUARD() { code } > + > + Is used at the head of a block to protect the code within the block. > + > +Note that 'goto'ing out of the guarded block will also drop the lock. > > DIFFERENCES WITH LINUX > ====================== > diff --git a/include/qemu/rcu.h b/include/qemu/rcu.h > index 22876d1428..3a8d4cf28b 100644 > --- a/include/qemu/rcu.h > +++ b/include/qemu/rcu.h > @@ -154,6 +154,31 @@ 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 *)(uintptr_t)0x1; > +} > + > +static inline void rcu_read_auto_unlock(RCUReadAuto *r) > +{ > + rcu_read_unlock(); > +} > + > +G_DEFINE_AUTOPTR_CLEANUP_FUNC(RCUReadAuto, rcu_read_auto_unlock) > + > +#define WITH_RCU_READ_LOCK_GUARD() \ > + WITH_RCU_READ_LOCK_GUARD_(_rcu_read_auto##__COUNTER__) > + > +#define WITH_RCU_READ_LOCK_GUARD_(var) \ > + for (g_autoptr(RCUReadAuto) var = rcu_read_auto_lock(); \ > + (var); rcu_read_auto_unlock(var), (var) = NULL) > + > +#define RCU_READ_LOCK_GUARD() \ > + g_autoptr(RCUReadAuto) _rcu_read_auto = rcu_read_auto_lock() > + > #ifdef __cplusplus > } > #endif > Acked-by: Paolo Bonzini