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rcu: Add automatically released rcu_read_lock variants 

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
   }

Note the 'unused' attribute is needed to work around clang bug:
  https://bugs.llvm.org/show_bug.cgi?id=43482

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20191007143642.301445-2-dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
This commit is contained in:
Dr. David Alan Gilbert 2019-10-07 15:36:37 +01:00
parent 8f8d528e73
commit 5626f8c6d4
2 changed files with 41 additions and 0 deletions
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16
docs/devel/rcu.txt
View File

@ -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
======================

25
include/qemu/rcu.h
View File

@ -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 __attribute__((unused)) = rcu_read_auto_lock()
#ifdef __cplusplus
}
#endif